Notes on Video Conversion
Contents:
[Document Version: 1.62]
[Last Updated: 05/25/1998]
Notes on Video Conversion
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All Rights Reserved
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Questions relating to various aspects of converting one video format (like
PC SVGA) to another (like NTSC) are very common.
Most of the articles in this document have been compiled over the last two
years based on replies from myself and others to postings on the USENET
newsgroups comp.sys.ibm.pc.hardware.video and those of the sci.electronics
hierarchy. I apologize if your response is not here - it could have been
that I missed the posting and will welcome contributions.
As always, comments, suggestions, and corrections are welcome.
Depending on the monitor, you may need a lot of electronics. VGA uses a
31.47 KHz horizontal scanning frequency - twice NTSC.
1. If it is auto-scan and goes down to 15 KHz horizontal, then you need an
NTSC to RGB converter. There are chips from companies like Sony,
Signetics, and others that will do this without too much pain.
2. If it will not sync at 15.734 KHz, you will need a real time digital scan
converter consisting of a video digitizer and a full frame buffer with
suitably fast I/O, For the special case of basic VGA, a subset of this
called a line doubler or scan doubler will get you a picture but it will
not be very good since it is not possible to achieve the correct type of
interleaving of even and odd video fields. See the section: "What is a scan doubler?".
For PAL (625/50) the relevant resolution is closer to 800x600.
There are boards for your PC that will take NTSC/PAL and put it into a window.
What you may find in the end is that your $150 TV gives you a better picture.
(The following from: Stan Rohrer )
For cards as well that take NTSC and put it into a window on your PO:
Check in the PC mail-order catalogs and your local PC parts outlets.
There are a number of TV boards and frame grabber boards that do what you
want. Prices start (I think) around $150. Professional level conversion
boxes soar above there somewhere.
I've just started investigating such devices. PC Zone (800-258-2088 for
orders/catalog) and MicroWarehouse (800-367-7080) carry Computer Eyes and
TelevEyes by Digital Vision. Prices here range from $300 to $600 with
the highest reported to include genlock and overlay capability.
PC Zone has an AITech TV board for $150. I don't know if it will take NTSC
video input or not. One of the guys I work with just bought an (unknown
brand) TV board that takes NTSC but he doesn't have it installed yet.
The hardware needed to watch TV on a typical high resolution fixed frequency
monitor would cost more than a nice large TV. In two words, forget it! In
addition to decoding the NTSC/PAL to RGB, the scan rates are SO different that
the only hope would be to build a full blown scan converter.
"How hard would it be to make my amber Hercules monitor display the output from
my VCR? the VCR has a RCA video output and a coaxial RF output and I want to
use the monitor as an orange TV."
This is almost certainly not worth the effort as the monitor accepts TTL (2
bits) and can display at most 4 gray (well, amber) levels without extensive
modifications. In addition, the scan rates differ substantially between
NTSC or PAL and the Hercules standard. As noted below and elsewhere in this
document, a CGA monitor with a composite video input would be a better choice.
(From: Jerry Penner (jpenner@sentex.net)).
You want to connect a Herc Mono TTL monitor to a composite video signal? Can
you say 'Big Waste of Time and Effort'? If you want a black and orange or
black and green TV screen, connect your RCA video output on your VCR to the
input of a composite CGA monitor. These monitors were used on Sanyo MBC
computers, and early Apple clones as well as some XT's. Colour composite
CGA monitors used to be used on C-64 and Vic-20 computers. Their usefulless
as TV/game monitors is legendary, and you'll be lucky to find a used one for
under CDN$80.
"I have a RGB CGA monitor and would like to use it to display a composite
or S-video signal from a VCR. I was wondering if anyone knows how to
accomplish this or knows of any economical products that will be able to
do this. Any info on S-video pinouts would also be greatly appreciated."
Is it strictly CGA? If so, that is TTL and you can forget about displaying
VCR S-video without extensive and not worth-it modifications. Some CGA
monitors have composite inputs or analog RGB inputs. With analog RGB inputs,
you need an NTSC to RGB converter. These can be built with a single chip and
some discrete components. There are probably converter boxes available as
well. If it accepts composite, then just use the normal video out from
your VCR. S-video won't gain you anything unless the monitor has separate
Y and C inputs as well.
I have a Magnavox CM8762-074T RGB Color Monitor which accepts both CGA TTL
and NTSC color composite video inputs. Locating monitors of this type may
be an alternative to video format conversion. These may be available for
next to nothing as the owners have upgraded and are often not interested in
(or aware of) their present utility. They are often of relatively high
quality and display a very nice picture since their original intended
resolution is similar to that of NTSC. I use the Magnavox CM8762-074T for
testing of VCRs and other baseband video sources.
Note: for the purposes of these discussion, the terms 'VGA' and 'SVGA' are
used somewhat interchangeably. However, strictly speaking:
* VGA refers to the basic original IBM VGA standard of 640 x 480 at 60 Hz.
* SVGA refers to scan rates greater than and including the basic VGA rate.
Both the signal format and scan rates are incompatible. Therefore, simple
conversion between analog VGA/SVGA and any of the TTL formats - Mono, CGA,
and EGA - is generally not realistically possible.
Some (mostly older high-end) monitors will accept multiple input types
like VGA, EGA, and composite. Two examples are the Mitsubishi AUM1371/81
and the Tatung CM1495. These can select between VGA and EGA input and the
Mitsubishi will also accept composite (NTSC) video.
For the general case of desiring to drive a true CGA-TTL monitor from a VGA
card, there are three options:
1. Replace the monitor with a VGA monitor.
2. Replace the video card with a CGA card if you can find one.
3. Completely redesign the CGA monitor to accept the VGA scan rate and analog
video input. Neither of these is easy or necessarily even possible and the
resolution of the CRT may be inadequate in any case.
If the monitor accepts analog RGB, it may be possible to program you VGA card
to put out the CGA (15.734 KHz) horizontal scan rate to be compatible with a
CGA monitor of this type. Your hardware and software may or may not support
this easily or at all.
If it's a true CGA monitor, there simply is no practical way to use it with a
VGA card. Period. If it's one of the original multisyncs that happens to work
with CGA, then there's some hope. However, these weren't so common: Sony 1302,
Mitsubishi AUM1381 or Diamond Scan, plus a few others). In this case, you just
need the proper cable and the appropriate switch settings for the monitor.
"We are trying to upgrade our print servers and have a lot of CGA monitors
and a lot of PS2 computers with VGA cards. We don't need more than 2
colors (mono) but when we make an adapter to connect the R to R, G to
G, B to B, H to H, V to V, Ground to Ground and the rest NC we don't
really get what is wanted.
Well, what happens is that the display is quite acceptable other than
the fact that there are two of everything on the screen indicating timing
problems. Covering the right side of the screen with a sheet of paper
works to cure the problem but a more acceptable solution is needed.
Adjustments to the monitor frequency, width, phase, H-hold, etc. don't help."
This is not surprising as the horizontal scan rates for VGA and CGA differ
by about a factor of two. This is much too large change for the monitor to
accommodate.
Note that CGA outputs TTL level signals (0 to 3-5V) and VGA outputs
analog levels (.7 V p-p). Therefore, what you have done may not work
in any case if the monitor expects strictly a TTL input. However, your
monitor must be compatible with the VGA levels.
The monitor would have to sync at double its normal scan rate for the picture
to properly fill the screen. First, it would be difficult to modify the
monitor for such a substantial change in horizontal scan rate. Second, and
more importantly, any such change could compromise the safety - stressing
the monitor's circuitry - increasing the risk of failure and the possible
fire hazard. Therefore, I would not recommend even making the attempt unless
you are quite knowledgeable in the design of monitor deflection circuits and
power supplies.
One other option other than replacing the video card or the monitor would be
to determine if your PC is capable of putting out CGA scan rate video. Many
video cards do have this capability not so much for CGA as for NTSC/PAL
compatibility. However, some programming or use of special video drivers
(software) may be required.
Alternatively, you may be able to find an inexpensive card that would be
able to provide the correct timing or even some old CGA cards that no
one wants anymore. Also, monochrome video rates are 18.43 KHz. If you can
find some MGA cards, you may be able to tweek the monitor that far.
Actually, for your intended application, painting over one half of the screen
isn't such a bad idea. :-)
The following applies with minor changes (scan rates, number of bits) to
MGA, CGA, EGA, and most other TTL video signal formats as well.
"I am trying to use an old Sony monitor, (PVM-1342Q), which only accepts a
CGA video signal through a 9 pin connector. My output is SVGA via a HD15
pin connector. Any suggestions on pin assignments or existing converters
to do the job?"
Assuming the monitor is actually CGA, it is probably not worth it. CGA
is TTL and SVGA is analog - you would need a converter and then only end
up with CGA's 8 colors or whatever.
The scan rates differ by a significant factor. If you can program your
VGA card for the monitor's horizontal scan rate (around 15.734 Hz - similar
to NTSC in the case of CGA), then the remaining problem is converting from
analog to TTL. This will require some high speed comparators and logic.
Questions about this specific problem are among the most common as low
cost fixed frequency monitors become available when their workstation
hosts are decommissioned due to the march of progress.
You will have to obtain the specs to have any idea of whether what you want
to do is possible. These are very often high resolution with a typical
horizontal scan rate of 64 KHz.
There are several issues:
1. Video compatibility - here is the one area where you are likely fine - your
monitor is probably compatible with VGA analog video levels - .7 V p-p.
2. Scan rate - your horizontal and vertical refresh rate. I would expect
that the monitor is not auto-scan and probably not compatible with
VGA or SVGA. Please check the specs if you have them or post a message
so that someone else can identify it. You need to know its horizontal
and vertical scan frequency range.
If it is fixed frequency, you will be able to use it only in your high
resolution (probably) applications. Booting the PC will require a normal
VGA monitor for the messages to be seen.
Assuming you are willing to use something else to boot and only run at a
single resolution, then the last hurdle is sync:
3. Sync. You have 5, 4, or 3 BNC (coax) connectors on the back of the monitor.
* 5 BNC connectors - this means that your likely have separate horizontal
and vertical (H and V) sync inputs - just what your VGA card wants. In
this case, as far as sync is concerned at least, all you need is a
VGA-to-5 BNC cable.
* 4 BNC connectors - this means that your monitor requires composite sync.
The H and V sync signals must be combined into one TTL level signal.
Some cards like those from ATI will probably drive it with just a VGA to
4 BNC cable since they can be programmed to generate composite sync with
no additional hardware. (Actually, get a VGA to 5 BNC - you just won't
use one of the syncs and this may come in handy at a later time).
You need to determine what its expected H and V rates are to see if they
fall within the range of the video card. Some internal twiddling may
be possible depending on the monitor. Also, the software size adjustment
in the ATI Install program also affect rates so that adds another couple
of degrees of freedom.
If you need to combine the H and V sync, a TTL gate, single transistor
circuit, or sometimes just a couple of resistors will do it.
For example, if you are able to program your video card for negative
sync polarity, then an AND gate (which will act as an OR for negative
logic) should do it. For positive sync polarity, a NOR gate or NPN
transistor will work. It is also possible to build an auto-polarity
switching circuit to accommodate any combination of positive and negative
sync polarities. In some cases, just using a resistor in series with
each sync line will be enough.
* 3 BNC Connectors - these monitors need what is known as 'sync-on-green'.
This will require some circuitry to combine the H+V+video into one
signal. The circuitry is quite simple if you are electronically handy.
Commercial boxes to do this are also available.
(From: Exar (exar@aol.com)).
For any type of video converters call ALTINEX,INC. in California
714-524-5400 they make a device that will combine sync, separate sync, put
it on Green, shift image left or right. Product name is DA1910SX. I have
several of them for my PC, MAC SGI and SUN.
See the documents: "Fixed Frequency Monitor FAQ" and "Sync-On-Green PC
Video FAQ" for details.
Some monitors have the required circuitry to accept separate sync
internally that is not brought out for a particular model. In this
case, some careful exploration may reveal hidden treasures.
So, check your scan rate. If that is not compatible, then you will need
a new display board anyway. If it is compatible, then you will just need the
sync combiner. Then there is the problem of booting DOS or Windows - these
usually want 640x400 at boot.
There are video cards designed for just this purpose. Whether the investment
is worth it compared with a new PC compatible monitor is questionable IMO.
See the document: "Notes on Approaches to Using Fixed Frequency Monitors on
PCs" for additional information and names of companies who manufacture the
special video adapters.
"Is there any way to modify an Apple 12-inch RGB color monitor
so that it can display 640x480 (instead of 512x384)?
Has anyone ever managed to do this? Any opinions on whether
or not it is possible?"
I assume you want VGA resolution - 31.4 KHz horizontal.
This would require changing the horizontal scan rate by a large amount and
is unlikely to be easily accomplished without extensive modifications to
the monitor's circuitry. This should not even be attempted unless you are
knowledgeable in the design of monitor deflection circuits and power supplies.
For other Apple (MacIntosh) monitors, see the section: "VGA to fixed frequency monitor (3, 4, or 5 BNC connectors)" as most of these run at
a fixed frequency. For example, the Mac II rate is 35.0 KHz H and
66.67 Hz V.
(From: jmz@southwind.net).
Most any multisync "VGA" style monitor will work with the GX, TX or CG3/CG6
frame buffers on a Sun Sparc. Commercial 13W3 cables and adapters are
available or you could get the instructions from a couple of places on the net.
I use my ViewSonic 17s on both Macs and Suns.
You should have a copy of Birdsall's Sun FAQ and you may wish to join the
Suns-at-Home mail list, for all Sun self-maintainers. Use a search engine for
these and they should vector you to the cable pinouts as well.
(From: Flupke ut Warns (P.O.Langemeijer@student.utwente.nl)).
The most important thing is to get the sync pin(s) connected and the
horizontal scan rate as close to the required value.
There is much more info and links at:
* http://www.ifi.uio.no/~karld/fixedsync.html
Realize that no matter what you do, the quality you get on the TV/VCR
is not going to be anywhere near what you see on the computer screen.
You must keep this in mind when designing layouts, selecting text fonts
and font sizes, etc. The new video cards with on-board NTSC/PAL output
should be better than your average cheap converter but don't expect
miracles.
"I need a bit of advice on converting VGA or SVGA to output suitable for a
color composite monitor and/or a regular NTSC standard television. I have seen
add on cards or outboard boxes that will convert VGA to standard TV but I am
not sure if this will have the same effect on a Color Composite Monitor. You
see I am wondering if it would be more cost effective to keep my old Apple
Color Composite Monitor and buy the necessary hardware to convert VGA output
from my IBM clone or to just go ahead and buy a bottom end 14" VGA monitor?
Can I even get true 24 bit 800 x 600 color performance out of a TV or a color
composite monitor?"
A color composite monitor may be somewhat better than a good TV but it is
still limited by the NTSC standard - mainly horizontal resolution but color
rendition as well. There is no way to get even basic VGA performance (640
x 480) from a TV or composite monitor.
You are much better off getting a bottom-end SVGA monitor for your PC. As
noted, the resolution of a TV or composite monitor is not even good enough
to do justice to VGA (640x480) when using the composite video input. Direct
RGB can be better but the pitch of the CRT relatively coarse dot or slot mask
or aperture grill is then likely to be the limiting factor. A composite
monitor or TV will give you approximately 480-490 lines vertically but 10
to 15 percent of these may be hidden by the CRT bezel due to overscan.
However, horizontal resolution is much worse. You will be lucky to get
half the VGA resolution (300 to 350 lines). For SVGA, there is simply no way
to display 800 x 600 without expensive scan conversion on such a tube and you
will not be able to read text or display clear graphics. In addition, since
the composite monitor or TV is interlaced, there will be annoying flicker of
graphics with thin horizontal lines.
Save your pennies - prices for basic monitors are dropping. Your Apple monitor
may work fine on your VCR, however.
This will only work if you can program the video card to produce a compatible
resolution and scan rate.
If you would like to experiment, here is a really simple circuit that may work
well enough for combining Hsync, Vsync, and one of the VGA color signals, say
green, into a composite video.
If the monitor sense lines on the VGA connector are tied MS1 (pin 12) = GND,
MS0 (pin 11) = no connect, then some programs will default to monochrome and
use a reasonable color map. I don't know how you will get a reasonable
mapping to monochrome for the others.
All you will need are 4 resistors.
I am calling your connector on the monitor 'Composite Video In'.
* Hsync through 500-1K ohm (R1) to Composite Video In.
* Vsync through 500-1K ohm (R2) to Composite Video In.
* Green Video through 200 ohm (R3 - variable) to Composite Video In.
* Green Video side of R3 to Ground through an 82 ohm (R4) resistor.
* Tie this ground to the BNC or RCA connector ground.
R1
Hsync o--------/\/\/------------+
|
R2 |
Vsync o--------/\/\/------------+
|
R3 |
Green Video o----+---/\/\/--+---------+--------o Composite Video In
| ^ | (Termination = Hi Z)
\ +----+
/ +--------o GND of monitor
\ R4 |
/ |
| |
GND (shield) o----+--------------------+
It is essential that all this be built as close to the monitor as possible
for best signal quality.
Set monitor video termination for Hi-Z. R4 provides the cable termination
to minimize reflections and ghosting of the green video signal.
Set your video card for negative sync polarity.
You may need to tweak these values for best results. This will depend on
your actual signals. The variable R3 may provide enough range for this.
"I am interested in converting a signal from my video card to a signal
that can be taken into the video in on my vcr. I realize that it is not
going to be easy. Still I would appreciate how to do it."
You are correct - this is not easy.
1. You need to convert RGB to NTSC or PAL - there are single chips for this.
Try Sony, Philips, Motorola, and others. These will combine the R, G, B,
Hsync, and Vsync into a single composite video signal using a minimum
of additional components. The same part can usually do either NTSC or
PAL by changing a jumper and possibly some of the external components.
For example:
(From: Brian B
"In the July 1996 issue of Electronics Now, a MC1377P (Motorola) is used
to convert RGB to NTSC/PAL. The chip can be purchased through the Newark
catalog. This chip is very easy to use and should make your circuit
simple."
Some other possibilities may be: ADV7175/ADV7176, UPC1352 (ECG/NTE1416).
2. You need to match the horizontal scan rate to NTSC (15.734 KHz) or PAL
(15.625 KHz). Even basic VGA is roughly twice this - 31.4 KHz. If your
video card can be programmed to put out interlaced NTSC or PAL rate video
then this is easy. If not, it is more difficult. If you want to use any
higher resolution than basic VGA (640x480) for a 60 Hz system or 800x600
for a 50 Hz system, it is a very non-trivial problem requiring a scan
converter which includes a video A-D, full frame store, interpolator,
readout timing, and video D-A. Unless you are an experienced digital
and analog designer, you really really do not want to tackle this.
For the special case of VGA to NTSC or PAL, you may be able to get away with
something less than a full blown scan converter. See the section: "What is a scan divider?".
You can also buy little boxes to do this. Quality is general not great
as you are seriously limited by NTSC/PAL and the VCR.
(From: Tomi Holger Engdahl (then@neppari.cs.hut.fi)).
There is all sorts of information relevant to video at:
http://www.hut.fi/~then/electronics/video.html
There is collection of links to RGB to NTSC/PAL converter and other video
chips at:
http://www.hut.fi/~then/electronics/video.html#chips
For more detail on this, check my circuit and related software at
http://www.hut.fi/~then/circuits/vga2tv/
Probably the most complete VGA to TV conversion pages in the web can be found
at:
http://www.hut.fi/Misc/Electronics/circuits/vga2tv/index.html.
There you can find schematics, drivers, tips, ideas, documents, links to
commercial products and much more. It does not have everything you need but it
is a good start. Going to composite video or RF is more complicated as there
are three composite video standard NTSC, PAL and SECAM in use in the world and
there are also some small differences in modifications of those used in
different countries) which is the reason why there are not much of this kind
of project. VGA to TV conversion is not simple technology either (the circuit
can be simple but there are quite many things to consider when designing such
circuit).
Homebuilt circuit persons should take a look at:
http://www.hut.fi/Misc/Electronics/circuits/vga2tv/index.html
There you can find my design of VGA to TV converter which outputs RGBS signals
suitable for TV SCART RGB input (I have also designed one with composite video
output, but that's for a commercial application). At the same page you can
find a PAL composite video output version of the circuit designed by Paulo
Coelho.
For introduction to scan conversion, check
http://www.extron.com/
Specifically:
http://www.extron.com/product/scanconv.html
Flickering is a problems always when yu do graphics to TV systems. The
graphics material must be designed so that flicker is not noticeable or the
scan converter box must include some kind of filtering to do the job.
NTSC/PAL system limit the bandwidth which makes picture to loose
some details. The picture is usually even worse than that, because of the
cheap video encoding chips used in many converters.
(From: Bill Sloman (sloman@sci.kun.nl)).
Try the Analog Devices AD721 and AD722. When I used the AD720, I had to add a
National Semiconductor LM1881 sync separator, and black-level clamps on the
red, green and blue inputs to get the right DC levels.
Check them out at http://www.analog.com
(From: Leon Heller (leon@lfheller.demon.co.uk)).
Raytheon has a chip which produces broadcast quality PAL/NTSC from VGA.
I think that Harris does one, as well.
(From: Kevin Centanni (kpc@panix.com)).
There are a couple of VGA-to-TV converter boxes that also output an NTSC
RGB signal. I own one from UMAX - I think it's called the TV-Mini. I
bought it from Global Computer Supplies for about $175. I also think
that MicroWarehouse sells this product. There's a model sold by AVer
also that has RGB out... but it's over $300.
The UMAX TV-Mini is a small box that plugs into your VGA card... it also
has a female VGA connector on it so you can display images on your
computer monitor and television monitor at the same time. The TV-Mini
is powered by the PC's keyboard connector. It has an RCA jack for
composite NTSC, an S-Video jack for s-video output and a Mini-8-DIN for
RGB output... if you go to UMAX's web page, they'll talk about how the
TV-Mini comes with an RGB SCART cable (SCART is a strange looking
connector that's used on many European televisions) - but it doesn't
come with this cable.
I was able to build a small adapter cable with some parts from
Digi-Key. The TV-Mini manual provides the Mini-9-DIN pinouts.
(From: Jerry G. (jerryg@total.net)).
I have played around with a few. The ones in the upper $300 to $400 are not
too bad. You will get a reasonable picture. I found the cheap ones are
extremely poor.
The best way to do it is with a video display card that has it built in.
These cards are expensive because the scan rate must be changed. There is a
lot of high speed ram and processing involved to do it right.
It is not a question of movement involved. It is a question of scan rate
conversion that makes things complex. With this conversion there is the
requirement of some complex quantizing to also convert the characters to match
as well. In a lower priced card that I have seen good results is the ATI card
with the NTSC output. I don't know the price of the card, but it is not
cheap...! There is a Targa card that is excellent, but the price is too high
unless you are in the business... But like I said, the higher the price, I
found the pictures
get better.
Also, the bandwidth for the fonts, and data comming through the conversion
is extremely wide. It is wider than off of a conventional TV broadcast, or
what comes out of a VCR. The TV set that you use must have a Video Component
input, and be able to handle at least 600 lines resolution or better. If not,
you will be cutting the performance of the signal right at the end! If your
TV has S-VHS capability, get the card with that option. It is better than
using encoded NTSC or PAL. The S-VHS mode keeps the color information
separate for processing. This allows for a better signal to noise in the
luminance signal, thus rendering cleaner pictures.
Please note, that you will never get the same picture out of a TV video
monitor as your computer monitor. They are based on very different processing
and CRT design. There are VGA Monitor projectors on the market, and I
would consider renting one for the casual use. It will certainly do a much
better job. This is what I recommend and do for my clients. Don't even think
about buying such a projector unless you have a lot of use for it. They are
extremely expensive, and require periodic maintenance.
(From: E. Abel (EugeneA1@worldnet.att.net)).
I've used an ATI 3D Expression+ PC2TV. The S-Video output is not bad,
although text is really not very crisp.
Surprisingly, the TV output from the Canopus Pure 3D card is much better.
Text is actually readable. (this is on a 27" Sony trinitron TV.) The Canopus
card uses a Chrontel chip to do the conversion.
Of course, at $190 the card is a little pricy.
This dialog resulted from the desire to construct a VGA to NTSC converter
to output PC video to a TV or VCR.
"I managed to construct a VGA to RGB converter so far, so I'm almost halfway
there, all I believe I need now is an RGB to NTSC converter circuit,
although i was trying to avoid the cost of buying one they sell in the PC
catalogs."
Can you program your video card to output 15,734 Hz H interlaced scan?
If so, you will have a lot less hassle.
"I figure the odds are in my favor by creating one myself, and as far as I
know, no harm could come to my computer by attempting it since the VGA/RGB is
and output only and not and I/O. Now since I already manged to convert my
VGA to RGB, hopefully you might be able to answer some specific questions
for me?"
"1. Is there a minimum & maximum resolution for a TV , or does that depend
on the size of the TV?"
If you mean resolvable spots on the TV screen, realistically, it is about
half VGA horizontally and perhaps a little more than half vertically or
about 320x300 give or take.
If you mean scan lines, that is pretty much fixed at 525 total interlaced
2:1 at 60/30 Hz (625 at 50/25 Hz for PAL 50 Hz systems) with about 420 (540)
actually visible on a typical TV. TV's are not auto-scan - they are designed
to run at a single scan rate.
Therefore, even displaying easily viewable VGA resolution will be tough.
A TV with an S-video input may do somewhat better.
(Remember when you had at most 40 characters across on a Commodore?)
"2. Assuming the construction of this circuit would only allow a maximum
output from my VGA card, what resolution would that be? 640x480 or 800x600
(I have no expectations of anything higher)"
As noted, for a regular TV, you can send it 640x480 but it will be
somewhat fussy. 800x600 is really out of the question. A high quality
TV-monitor might do VGA ok. The actual number of lines on a TV is, of
course, only about 480 active with perhaps only 420 visible due to
the CRT bezel. Unlike an auto-scan monitor, you don't get easy control
of this and no control of the number of lines.
"3. Finally, taking into consideration the limitations of such a device, I
only intend for this to be used for full motion video playback, as my
current video capture card, as well as all other cards currently on the
market, lack the ability to output the video back to the original source
(i.e. a VCR or camcorder).
Unfortunately, even expensive solutions are still limited by NTSC. However,
since your playback is often at reduced resolution (e.g., MPEG) to begin with,
this may be acceptable.
(From: FoulDragon (fouldragon@aol.com)).
I'll warn you: You can get a box that will make your PC display on a TV, but
it will not be worth your while. We use them at our school, they cost from
US $100 and up, and the picture, even on a good TV is very poor. If you can
afford one of those boxes, buy a used VGA [even monochrome] and use that as
you will be much happier.
(From: Terry Lin (tlin@servtech.com)).
I find that with the ATI PC2TV, on a S-Video hookup on a Sony XBR, the image
quality is pretty decent. The flicker removal makes even a full white screen
easy to look at (provided you have the contrast turned down, which should be
done on every set). I have seen what poor external boxes can do, they give me
adaches with the flicker and blurriness. Just make sure your setup is right
before evaluating the entire PC to TV monitor thing.
(From: Jon Jenkins (jenkinsj@ozy.dec.com)).
I use standard 74HC 14pin DIP gates available from any electronics store. I use
a 14 pin DIP socket originally so that I could change gate types (OR/XOR/AND)
easily. 74HC86 (XOR) works just great with the VR320 (I am using it now can
also use OR, don't understand why ??).
The VN10KM is a small signal N channel enhancement mode MOSFET also available
from most electronics store.
If the video card you are using is a standard VGA output (I'm using a diamond
stealth 64 VRAM):
Pin 1: Red video
Pin 2: Green video
Pin 3: Blue video
Pin 4: Monitor ID bit 2
Pin 5: Ground
Pin 6: Red return
Pin 7: Green return
Pin 8: Blue return
Pin 9: NC
Pin 10: Sync return
Pin 11: Monitor ID bit 0
Pin 12: Monitor Id bit 1
Pin 13: H sync
Pin 14: V sync
Pin 15: NC
I join all the "returns" together with the ground on the small PCB and use
that as a common ground for the RGB cable to the monitor. You can use separate
if you want to but you should join the green return and sync returns together.
I did find some small shadowing if I didn't group them all together.
Just a note, when you set up your video card in Windows (or Win95) set it
to 1280x1024x72|66 or whatever is closest. I use a VR260 (1024x864) at
1027x768@66Hz (check with your manual DA or D4 are 72Hz) your VGA will not
like this frequency so either disconnect it quickly or before you actually
set the video card to this mode (i.e. put the OK as the active control in
Windows and then connect the VR320 and hit return) My diamond setup gives
me 10 seconds to do this adjustment When you exit you will probably have
to select the 1280x1024 mode with your old VGA connected again and from then
on every time you start Windows you will be able to view it in "big" colour
mode. Note the vr320 will not work in DOS mode as it is not an auto-scan
monitor so all you see when you boot up is garbage until Windows starts, I
put "win" in my autoexec.bat file.
Note there is a danger here: I had set up the monitor and for some reason it
did not work so I couldn't see what was going on: my old VGA wouldn't work and
the VR wouldn't work either so I had to find the cards .ini files and edit by
hand to get back to usable video!!
For FreeBSD/XF86 the lines are:
#VR260 monitor is 70MHz 1024x864
#VR320/319 monitor is 130MHz 1280x1024
Modeline
"1280x1024" 130.81 1280 1312 1472 1696 1024 1027 1030 1063 +hsync +vsync
Modeline
"1024x864" 69.2 1024 1040 1168 1272 864 864 867 904 +hsync +vsync
The circuit to do this is as follows:
Notes:
1. You may be dealing with 135MHz square waves so there are lots of high
frequency stuff around; use good RF practices.
2. The coupling capacitors are a safeguard to start with. I don't use them
because they caused shadowing around sharp colour changes (the old RC
effect).
3. Use the XOR gate first as a test but you may need other gates to actually
get it working.
4. An oscilloscope will be handy for final adjustment.
5. Make the device is as close as possible to the video outlet on the VGA card.
6. Take the 5V from the PC power supply inside the box. I just hooked one of
the spare connectors which I also use for an external fan (Pentiums being
the heaters they are!). Make sure (check it again!!) (and again!!!) you
don't get the 12V one!!
7. You must use a VN10KM or other small signal N-channel enhancement mode
MOSFET. Others will not work!!
+5 V
o
|
/
\ VR1 (1k carbon mini pot)
/ (Warning: don't let this go near zero!)
\
33uF tantalum | ~0.3V DC in porch area
GREEN o----+----||-----+----------------------+---o GREEN to monitor
+----||-----+ |
.1-.01uF ceramic |
|
Gnd |
o |
| |
/ |
\ 47k |
| _|
HSYNC o-+----|-------\ |
| GATE |------CSYNC----+----|| VN10KM or similar small
VSYNC o-+----|-------/ | |_ N channel enhancement MOSFET
| \ |
\ / 47K o
/ \ Gnd
\ 47K /
/ |
| o
gnd gnd
HSYNC, VSYNC and CSYNC are grounded with 47k carbon resistors
Gate type=LS or HC types, HC preferred:
* OR: for -ve logic sync and no hsync during vsync.
* NAND: for +ve logic sync and no hsync during vsync.
* XOR: for -ve or +ve logic sync and hsync during vsync.
Capacitors are optional, I don't use them.
Use XOR gate with DEC monitors and as a first shot with others, then OR gate
then NAND gate.
Get an oscilloscope and adjust porch levels to 0.3V and 0 level (sync level)
to 0.0V
This requires matching the scan rates and implementing a suitable digital
to analog converter to take the TTL data and produce analog signals.
A scan converter can be used on the analog signals once they are generated
to adapt the video to your monitor. However, I don't know if scan converters
with suitable input and/or output capabilities exist.
The digital to analog conversion can be done with a few resistors if you
are not terribly fussy about the quality. For example, the following
circuit should be able to generate a reasonable VGA signal from a 2 bit
input (e.g., MGA or one of the EGA color channels):
450 ohms
Bit 1 (MSB) o--------/\/\/------------+
|
900 ohms |
Bit 0 (LSB) o--------/\/\/------------+-------+----o Analog video signal
|
/
\ 75 ohms (termination, may
/ be inside monitor).
\
|
Ground o--------------------------------------+----o Monitor Ground
This assumes the H and V sync are separate signals. If this is not the
case, these will need to be combined into this signal (at least one
of the channels) as well.
I have not tested this circuit. Using low value pullups on the TTL
signals (say 220 ohms) should help improve the high level consistency.
From: jcaldwel@iquest.net (Mr. Caldwell)
It is a CGA frequency only monitor. It has an 8 pin analog jack on the back
and may have a 5 pin ttl jack and ttl to analog converter inside for
standard CGA, you can use a cable for the analog plug to a 9 pin d plug for
MCGA and get 320 x 200 by 16 Million colors. Some IBM cards will put out the
correct frequency and analog signal, most won't. I used an ATI Wonder VGA
card that would work correctly *if* manually configured.
Otherwise you need a VGA to NTSC converter. See the section: "VGA to NTSC or PAL" for more information.
"I am trying to build a circuit to convert the RGB output of a video game to
my large screen TV.
(From: Leon Heller (Leon@lfheller.demon.co.uk)).
If the game outputs VGA, Raytheon has a chip, the TMC2360, which
converts it to broadcast quality PAL/NTSC video.
I have no idea of what this gadget actually does but it may be worth checking
out:
(From: James Willcox (jwillcox@spitfire.net)).
Boca makes an adapter. I have one and it works fine. It has little switches
on it to select resolution and refresh rate.
"Does anyone know how to convert a video out signal into a signal
usable by a CGA monitor (RGB + H and V sync)?"
If your CGA monitor is TTL, then it may not be possible, at least not
without modifications to the monitor. You need to convert from NTSC to RGB.
There are single chips (with a few external components) solutions to this.
Try Sony, Philips/Signetics, and Analog Devices (I think) as well as others.
These take NTSC (or PAL) and output RGB and sync. CGA is not analog
(continuous range of video values). It is TTL with Red, Green, and Blue
signals as well as a separate Intensity signal. Unless your CGA monitor can
take analog video (.7 V p-p) inputs, you will still only be able to get
8 or 16 colors - not a normal TV picture. (And even for that, you will
need external circuitry to convert the analog output of the decoder chip
to TTL.)
However, some CGA monitors have internal NTSC composite inputs and in
that case, it is simply a matter of flipping the appropriate switch.
Several companies provide single ship solutions requiring only the addition of
a few discrete components to convert NTSC or PAL to RGB and H+V or C sync.
Some have options for YIQ, S-Video, and other formats at the input or output
in as well.
Check out the web sites or databooks of Sony, Philips, Brooktree, Motorola,
Linear Technology, etc.
For example, Motorola offers the MC44011. The datasheet can be found at:
http://design-net.com/books/dl128/gifs/mc44011rev1f.1.gif.
This part can be used without an external delay line (for PAL to RGB) but a
delay is recommended. The chip also provides an A/D sampling clock output
for video digitizing applications.
It is possible to search the Motorola site from for other parts or application
notes from: http://design-net.com/cgi-bin/dlsrch.
(From: Jeremy Todd (bulb@cix.compulink.co.uk)).
Sony makes at least two PAL decoder chips - CXA1621S and V7021.
It looks like you'd need a separate sync stripper (LM1881 or EL4581CN)
Brooktree's Bt812KHF is a much fancier thing for video processing and
multimedia stuff.
From RS(UK) both the Sony chips are 10UKP each for 1 off's. The Bt812KHF
is 107UKP!!
(From: Sam).
Also, some questions are along the lines of the following:
"I looked at several chip manufacturers. Most have extensive documentation
on their chips in PDF format. Again, most of the chips currently available
convert Y/C to digital RGB, and have a lot of extra brightness/sharpness
control built in. Too complex- the simplest chip I came across was 18 pins
and still required two dozen external components."
(From: Eugene (eugenek@istar.ca)).
The answer is: MC44011 by Motorola, cost $28(Can). It requires some sort of a
micro to program it (PIC or the like will do).
There is no external critical components except for a 14.318MHz crystal (found
on any PC motherboard).
About the old TV single-chip decoders. This is not true, I've been working
with those things for 15 years, and in 70-80s the decoders were much more
complicated than they are now (each decoder, actually, requires a delay line
(sometimes more than one) and a bunch of various filters). Yes, you had one
chip and half a dozen of coils, trim-caps to tune (that required some
equipment and knowledge).
Sorry, the chip I suggest has 44pins :-( but little hassle :-)
"I'm wondering whether I could use my NEC Multisync as a TV. Long ago
I had a Mitsubishi Colour Monitor which could also be directly connected
to the videorecorder. Sure, I could use cards in my PC like "WIN/TV",
but then every time I want to look TV I have to switch on the PC as well.
Is there the possibility to convert a video to a VGA signal? My NEC has
only a VGA input. Or: Are there any monitors available which have both
inputs (like my old Mitsubishi)?"
"I have a VGA monitor That I want to use to watch TV. I want to be able
to maybe build a box that will let me plug a vcr video out into the monitor.
I do not want to spend tons of $$$$$. Can anyone tell me if there is a way
to do this??"
"I have a HI-FI VHS that is attached to my stereo. Therefore, my audio needs
are well taken care of. I now need the video. I had to sell my TV a little
while ago so I do not have a T.V. at this point. I have recently acquired a
20" monitor for my PC (DFI brand.) It has the RGB (red-green-blue) connectors
on the back along with a Horizontal and Vertical cable connections. So I have
a cable that plugs into my video board on my PC that turns into 5 connectors
at the end that connects to the monitor."
"Does anyone have any information on viewing composite video on SVGA
type monitors. I have a MAGNAVOX SVGA monitor and if possible I'd like
to feed composite video from my VCR and Sony PSX and PANASONIC 3D0 to
it. Rather than getting a Toshiba TIMM monitor there has to be some
kind of blackbox that will allow someone to do this...Please send info
to the address provided or post here."
It depends on your monitor:
1. The monitor needs to support the NTSC scan rate - 15,734 H, 60 V. Some NECs
do (like the 3D) but others do not (like the 2A).
2. You need to convert NTSC to RGB. There are boxes on the market for this
or if you are handy with electronics, single chips to do this. Check out
Sony, Philips, Analog Devices, Motorola, and others for NTSC/PAL to RGB
decoder chips.
For PAL (625/50) the relevant resolution is closer to 800x600.
If your PC monitor scans down to 15.734 KHz, then all you need to do is
convert the line level NTSC composite to RGB and sync. Some older
auto-scan monitors like the Mitsubishi AUM1381 even have a composite
NTSC input jack. Conversion requires a single chip and a few discrete
components. Commercial converter boxes are also available.
However, if it is a modern SVGA/auto-scan that does not go below 31.4 KHz,
then it is a non-trivial problem requiring a video A/D, frame memory,
readout electronics, video D/A, etc. This is called a scan converter
and is not an afternoon project even for an experienced design engineer.
You can of course buy PC cards that will enable you to watch TV in a
window on you PC.
There are also external boxes that will accept antenna/cable or NTSC/PAL
composite input and drive a VGA monitor. One such unit is the 'Proview'
(Proview Technology, Garden Grove, CA). This is reviewed in Popular
Electronics, June, 1997. It appears to be quite capable with its own internal
181 channel tuner and IR remote control. It accepts both RF (antenna or cable)
and composite inputs and can select between the video source or computer to
drive the monitor (but does no processing of the computer's VGA signal - full
screen only). With a suggested list price of $119, the Proview could represent
a cost effective alternative to a new TV if you have a VGA monitor sitting
around collecting dust.
Some others can be found at:
* http://www.aver.com/lite/products/avertvgenie.html
* http://www.aimslab.com/Products/InstantTV/f_Instanttv%20home%20page.htm
(I have no personal experience with any of the above products --- sam).
In any case, a $150 TV may actually produce a better picture. This is because
the CRT/electronics in a computer monitor is optimized for focus at the expense
of brightness. Therefore, sharpness may actually be excessive and brightness
may be inadequate except under subdued lighting conditions (especially on a
well worn monitor!).
(From: Helmut Weber (Helmut.Weber@hamburg.sc.philips.com)).
There are some companies that have boards ready, which you only
have to buy and plug into your PC. Try:
* http://www.como.com
* http://www.miro.com
* http://www.2fast4u.com
You need a lot more than cables. Here are some comments:
1. Your SVGA monitor must be able to sync down to 15,735 Hz Horizontal - the
NTSC scan rate - this is CGA speed and few modern monitors go this low.
You thus need a scan converter - not cheap.
2. You need to convert the composite video or S-video out from your VCR into
separate RGB and possibly H and V sync. This means electronics not
just wires.
3. You will need a good switchbox to select between the sources, you cannot
just hook them together.
4. The quality of the TV video on your expensive SVGA monitor will likely
be worse than on a $150 TV due to the fine focus of the monitor and
the possibly lower brightness. To put it simply, the monitor is too
good for NTSC video.
5. Why tie up your computer system watching TV? The other alternative is
to get one of those TV tuner and/or frame grabber cards for the PC.
"Does anyone know of a simple way to convert NTSC signals produced by
American video equipment to UK PAL signals."
If you simply mean the color conversion, then a couple of chips will do it.
There are chips to do RGB to NTSC or PAL color encoding but not, as far as I
know, scan conversion. For your needs, look into Sony, Philips, and Analog
Devices, Motorola, and others.
As has been pointed out, using the strict definition of NTSC to PAL as
referring only to the color encoding, all you need is a couple of chips for
NTSC to RGB and then RGB to PAL, maybe even a single chip. However, for the
very common interpretation of NTSC to PAL (IMHO, maybe a little USA-biased) is
with respect to US NTSC 525 line 60 Hz systems to PAL 625 50 Hz systems which
is where the non-trivial part comes in.
If what you really mean is NTSC 525/60Hz to PAL 625/50 Hz, it's not trivial.
* The horizontal and vertical scan rates differ 15734 vs. 15625.
* The number of lines/frame differ 525 vs. 625.
* The color encoding differs.
If you simply want to watch an NTSC tape on a PAL TV it may work but not with
proper color if the vertical has a wide enough range to sync or you have a
vertical hold control with enough range. If your intent is to put it into a
VCR, you can safely forget it.
The usual way is to use a scan converter. Essentially, an NTSC color
decoder/A-D feeds a frame buffer (approximately VGA size). The frame buffer
is then read out at PAL rates and the necessary interpolation is performed
using digital processing to go from 525 (480 or so active) to 625 (580 or so
active) lines. The output is sent to a video DAC and then color encoded for
the PAL system. Everything all happens in real-time.
Needless to say, this is not your basic hobbiest afternoon project.
Here are some additional comments:
(From: Clive Tobin (tobin@nwus.com)).
Conversion is not a trivial matter, involving interpolating scanning lines,
changing the field rate, and changing the color encoding scheme. I am not
aware of a simple chip set that will do it. There are several ways of doing it
with bought equipment, listed in order of increasing price:
1. If you can stand to look at it on your computer instead of your TV, you can
buy TV tuner cards with video input jacks, that will display NTSC on your
VGA computer screen. I think I have seen these for around $100.
2. Buy a multistandard TV, which are becoming increasingly popular and don't
cost much more than single-standard ones. You would not need an NTSC tuner
if it has a video input jack. (I don't know if your camera has an RF
modulator as well as a video output.)
3. Buy a standards converting VCR, such as Aiwa HV-MX1, Samsung SV-4000W, or
similar. These can be used as a stand-alone converter, or to convert the
video to record tapes in a different standard. These sell for around $600
and up. I think they all have RF modulators to feed your TV set if it is
lacking a video input jack. If you get one of these you could go into the
standards conversion business, converting home tapes of overseas
relatives.
Editor's note: Not all multi-standard VCRs do what you want. Some/many
simply convert the color encoding between NTSC and PAL without affecting
the scan rate (which is much more difficult/expensive). A wide vertical
range TV or monitor might produce a viewable picture with these but at the
wrong speed (off by 5/6 or 6/5 including the sound)! Unless the product
specifications clearly state 'full conversion' or 'scan rate conversion' or
something similar, you can probably assume they take the cheap way out!
Make sure you can return the VCR if it doesn't meet your needs! --- sam.
The cheapest of all, if you can stand to see the image in black and white with
the vertical size off, would be to plug it into the video input jack of a PAL
monitor that has a wide-range vertical hold control. Don't use the RF
(antenna) input of a regular TV as it may not work at all because of the
different carrier frequencies. (You did buy one with video and audio jacks,
didn't you?)
(From: Geoffrey S. Mendelson (geoffm@pita.cs.huji.ac.il)).
There are digital converters that do this "on the fly". Akai (and Radio Shack
in the US) sell a VCR for $500-600 (US) that works well. Panasonic sells the
AG-W1 (NV-W1) that is an excellent VCR and a much better converter for about
$1800.
You can also buy just the converters.
Avoid VCR's that claim to play PAL tapes on NTSC TVs. They convert the color
signal from PAL to NTSC (well enough for the kiddies to watch tapes), but
assume you can "stretch" the sync of your tv to work with 50Hz video.
A scan converter accepts video of one format - say SVGA - and outputs it to
some other format - say NTSC. Some are designed for fixed input format while
others can adapt - possibly automatically like an auto-scan monitor - to a
wide range of input scan rates and resolutions. Output format is most often
selectable between NTSC and PAL scan rates (or those of other TV formats) with
a variety of output options such as composite, RGB, SCART, and S-VHS.
The typical scan converter must implement the following functions. (This
example applies to a unit designed to convert from SVGA or workstation
video format to NTSC):
1. Analog to digital converter (A-D or ADC). In the case of VGA/SVGA or
workstation video, there will be 3 video signals - R, G, and B - and each
of these must be digitized separately. The A-Ds used are generally single
chip 'flash' types using a bank of voltage comparators (e.g., 255 compares
for 8 bits of output precision) or similar technique to achieve the high
speed conversion needed in modern video applications. These may be able
to convert up to 135 M samples per second or more as they must run at the
dot clock rate of the RAMDAC of the input video source. A filter (input
anti-aliasing) may be needed to limit the bandwidth of the input signal.
Ideally, the sampling will be adjusted to occur at the center of each
pixel but this is not always possible.
2. Full frame store. The resulting digitized data - usually 6 to 8 bits for
each color - is stored in a frame buffer generally constructed from DRAM
or VRAM. This memory must be capable of being written to and read out
effectively at the same time - dual port or pseudo-dual port. In some
special cases, less memory is needed but these are the exceptions. With
VRAM, the input may use the serial port since it is strictly sequential
(and very high speed) and the readout can use the random access port for
interpolation (since its rate is lower but multiple pixels and lines may
need to be accessed, see below).
3. Readout and interpolation. Hardware must be able to access the frame store
without conflict at the desired output scan rate. Since the output video
format has a different (generally fewer) number of pixels per line and
total scan lines, some means must be provided to combine multiple pixels
and lines into the output video stream. For interlaced output (as used
by most TV standards), some amount of interpolation between lines (in the
vertical direction) is desirable to reduce the flicker of fine horizontal
lines (in graphical material) which would otherwise fall in a single output
video field. For RGB full color, there is a separate interpolator for each
color channel.
* Nearest neighbor interpolation simply uses the closest sample from the
stored data. This is very easy to implement since it is just a matter
of computing a memory address - often by just truncating bits. However,
quality is poor - pixelly - and usually unacceptable for all but the
least critical and cheapest applications.
* Bi-Linear interpolation takes pairs of input pixels in the horizontal
and vertical direction and combines them to form an output pixel that
is their weighted sum. This results in a much smoother and more pleasing
display. Since two pixels on each line and and two lines are required
for the computation of each output pixel, the bandwidth requirements of
the frame store and processing complexity are greater resulting in a more
expensive system. However, this is the minimum level of interpolation
required to produce decent quality output video.
* Cubic or higher order interpolation uses more than two points in each
direction resulting in somewhat better results at greatly increased
cost. This is likely to be found mostly in the high performance
professional equipment used in television studios and production houses.
The output of the interpolator is typically 6 to 10 bits of data for each
color channel.
4. Video digital-to-analog (D-A or DAC) converter. A high speed DAC (three
for RGB) converts the each of the interpolated data streams to an analog
signal. A filter (output anti-aliasing) may be needed to smooth edge
transitions.
* For driving RGB monitors, this is the final output.
* For NTSC or PAL, RGB along with H and V sync are further processed by an
RGB-to-NTSC/PAL encoder. It may output be composite video as well as
separate Y and C to provide for various output connector options: RCA
or BNC, S-VHS, SCART, etc.
5. Microprocessor control. Most modern scan converters use sophisticated
computer control to provide for advanced levels of auto-scan, many user
conveniences, stored setups, and so forth. Features may includes various
amounts of user or RS232 (PC) controlled pan, scroll, and zoom; control
of sampling times and speeds; and selectable levels of interpolation to
control smoothness or sharpness.
However, in the end, no matter how the scan converter is implemented, if the
ultimate destination is an NTSC or PAL TV, the resulting picture quality will
be very limited. Even a $20,000 professional scan converter may not be able
to display fully legible VGA on an NTSC or PAL TV.
For more information on features and selections of scan converters, try:
http://www.extron.com/scancon.htm.
(I have no affiliations with this company and am in no way necessarily
endorsing any of their products or claims.)
Implementing a system of this type is a challenging task even for an
experienced engineer with extensive design experience with both analog
and digital systems.
(From: Derek Roberts (der@cam-orl.co.uk)).
If you really want to do this properly, check out the Genesis Microchip
gmVLD8 which uses DSP techniques to do the un-interlacing. Of course you
need to add an A-D, field or frame store and some control, But this is
the basis of a decent quality scan converter.
This is a special case of a scan converter where the output format has roughly
twice the number of lines as the input format and runs at twice the horizontal
scan rate.
The following is described for NTSC; A similar approach can be taken with PAL
625/50 to SVGA at 800x600, 50 Hz.
To convert NTSC interlaced at 30 frames/second 60 fields per second to
VGA which is at 60 complete non-interlaced frames per second requires
a simple scan converter. This is basically an NTSC color decoder and
video A/D feeding a full frame memory storing RGB (probably at 24 bits), and
VGA video D/A. I say simple to compare it to the general case where in
addition to frame store, you need a high speed interpolator to convert
between resolutions. VGA is close enough to NTSC resolution (at least
in terms of the number of active video lines) that no interpolation is
needed. See the section: "What is a scan converter?". In either case,
this is a non-trivial project. IMHO, this is a poor use of an expensive
monitor. A $200 TV will likely look better.
An even simpler approach is possible as well which only requires a one or two
line buffers instead of a full frame store. Each input line is read in and
reformatted to the appropriate VGA line (even or odd) depending on which field
is being displayed. The other lines are blanked (i.e., display even lines and
blank the odd lines during the even field display). This would only require
enough buffer memory for one or two scan lines (depending on whether the
implementation uses a double buffer or more sophisticated write and read
timing) which would be a significant cost and complexity savings compared
to a full frame store. The disadvantage is that since half the lines are
by necessity left blank, the maximum possible brightness of the display will
be reduced. It is not possible to use the blank lines as the interleaving
of the even and odd fields will be incorrect and result in a poor display.
For the special case of converting from VGA at 640x480 (31.4 KHz H, 60 Hz V)
to NTSC or SVGA at 800x600 (31.4 KHz H, 50 Hz V) to PAL, something simpler
than a full blown scan converter may be satisfactory. In this case, it is
only necessary to provide storage for a single scan line (rather than an
entire frame store) since the input horizontal frequency is (almost) exactly
twice that of NTSC (15.734 KHz) or PAL (15.625 KHz). A double buffer where
one buffer is storing while the other is reading out at approximately half
the VGA pixel rate should work. With appropriate timing, even lines become
the even field and odd lines become the odd field (I may have this backwards).
It is still not a trivial undertaking. Keep in mind that the quality you will
get on NTSC or PAL will be poorer than the VGA due to fundamental NTSC or PAL
bandwidth limitations. Also, flicker for line graphics will be significant
due to the interlacing at 30 Hz.
"I'd appreciate on an Integrated Circuit (IC) made by a Hong Kong company
called Display Research Laboratory."
(From: Philip Decker (pdecker@lds.loral.com)).
The IC is a Video Interlace Processor (VIP), part number VIP-01033. It
converts 16-bit digital VGA video (5:6:5, R:G:B) to similarly formatted
NTSC/PAL compatible video.
The IC can also be bought as part of a circuit board with additional
components, producing composite, Y/C, and SCART analog RGB outputs, in
three different configurations:
* piggy-back to VGA, via feature connector ($55)
* external VGA to TV converter ($90)
* ISA bus card with VGA included ($180)
"I'm looking for a simple GOOD black level clamp circuit for clamping a
video signal."
(From: Joseph H Allen (jhallen@world.std.com)).
This is actually a very interesting subject. Assuming you have a constant
video level (or AGC), a simple diode clamp on the horizontal sync tips
(diode clamp the sync so that the black level is where you want it) is
actually a high quality black level clamp. The sync level is constant after
all. I use this method in accurate video digitizers for DC restoring the
video before putting it into an A/D converter. The cool thing about simple
diode DC restorers is that the capacitance is usually much less than that of
the analog switches needed in other types. For example one of the best
analog switches is the readily available 74HC4316, but even this has 40pF
(if memory serves) on its pins.
The really hard part is finding a high quality large-signal linear video
amplifier. If the video is capacitor coupled to the video amp, then the
average brightness level will change the voltage of the black and sync
levels seen by the amplifier. This is ok if the video amp is linear, but
most aren't so the sync amplitude ends up changing depending on brightness.
I.e., the black level will change depending on the brightness of the image
(this is completely unacceptable for medical image capturing devices, for
example).
The way linearity is measured for video amplifiers is the term "differential
gain". It gives the largest difference in percent between a constant
small amplitude signal (traditionally the color carrier is used for this)
measured at different voltage levels (hopefully which sweep the entire
output swing of the video amplifier).
Now you have to be very careful about manufactures differential gain
measurements. Many of them play games to get even a mediocre 3% - 1%
differential gain. Typically they specify this parameter with a reduced
output range (when you really want the parameter to apply to rail-to-rail
output swings so you can get a 2V signal needed for most A/D converters) or
limit the input range, the gain or flat out lie (I have no idea where
comLinear got the specs for their clc520/522 variable gain amplifier, for
example. It says .5% in the datasheet, but I measure it to be more like 5%).
All older video amplifier ICs (like the uA722 and NE592) are really lousy.
Discrete transistor amplifiers also suck (many monitors use a cascode
amplifier which is very bad). Most new ICs suck too- especially those which
are labeled as video amplifiers. The only ones which I have been satisfied
with are the newest current feedback OP-amps (the + side is high-impedance,
but the - side is zero ohms. Usual op-amps are linear, but have a limited
bandwidth because the - input is high impedance). These have enough
open-loop gain so that they really are linear. One that I really like is
the AD9617: .01% differential gain (!), 160MHz bandwidth, immense slew rate
(settles to less than 1% of final value within 10ns or so) and only costs
about $10.
If you need variable gain (for AGC perhaps), the best chip to use the AD834
500MHz multiplier. This little 8-pin chip is expensive (like $40) but it is
the only thing that even approaches being linear (and even it is quite a bit
worse than the AD9617).
(From: Brian Campanotti (bcampano@toronto.cbc.ca)).
Look at the Clamping ICs from Gennum Corp (part numbers GB4550
and GB4551). They do input buffering and clamping. They are
a good front end to any video project.
(From: Mika Iisakkila (iisakkil@alpha.hut.fi)).
Since your application probably needs some kind of an input/output buffer
anyway, you might consider some integrated DC restored video amplifier.
Elantec makes excellent such chips; data sheets are available on their web
site under "application specific: video".
EL2090 is really good as far as video quality goes, but a bit
expensive for applications that don't need 100 MHz bandwidth and
near-zero droop. EL4089 is simpler and cheaper, but not quite
"broadcast" quality. There's also some new chip, but I haven't looked
into it yet.
For both chips, you'll need to get the sample pulse from somewhere, so
you can't lose the LM1881. I've used the burst gate output from it to
control 2090's sample input, and quality of the result far surpasses
my measuring instruments.
(From: Gary L. Sanders (75052.2665@CompuServe.COM)).
Philips has chips, as does Raytheon, these would take digital RGB
and convert to oversampled PAL output. Check out my web page
analog filter modules that are low cost and provide all of the
interface needed for top performance from the encoder to the PAL
or NTSC output. These are the ST-120 and ST-125 modules. They
work with all oversampled digital encoder (RGB to NTSC/PAL)
chips. This is the highest quality way to go and it results in a
small low cost module with NO adjustments, as with analog encoder
chips.
(From: Mike Diack (moby@kcbbs.gen.nz)).
Analog devices does a chip (AD720) which has the delay & filter elements
on the chip itself.
The assumption here is that the input is an NTSC or PAL composite video signal
and that the desired output is a valid composite waveform with negative sync
tips. In this case, what is required is as follows:
* Sync separation to identify and preserve the sync relationships.
* NTSC or PAL to RGB conversion.
* Inversion of the individual RGB components.
* RGB to NTSC or PAL conversion along with the sync.
Bypassing the conversions would be messy as you would be dealing the chroma
phase space - I wouldn't even want to risk a wild guess as to what would be
involved.
For monochrome video, the conversion steps would be replaced with a simple
inverting amplifier and possibly an analog switch to merge the sync.
(From: Joel Kolstad (kolstadj@CSOS.ORST.EDU)).
Also note that straight video signal inversion will produce some...
interesting... color changes, but not the same changes as you get from
photographic film. For monochrome video, the end result will look like
a photographic negative.
Luminance Specifications:
VHS (240 lines) - FM Dev: 1 Mhz; Freq Range: 3.4-4.4 Mhz. (Sync tip - White)
SVHS (400 lines) - FM Dev: 1.6 Mhz; Freq Range: 5.4-7 Mhz.
BETA1 (250 lines) - FM Dev: 1.3 Mhz; Freq Range: 3.5-4.8 Mhz.
BETA2/3 (240 lines) - FM Dev: 1.2 Mhz; Freq Range: 3.6-4.8 Mhz.
SuperBETA (285 lines) - FM Dev: 1.2 Mhz; Freq Range: 4,4-5.6 Mhz.
ED BETA (500 lines) - FM Dev: 2.5 Mhz; Freq Range: 6.8-9.3 Mhz.
The above refers to resolvable horizontal resolution - the maximum number of
vertical lines that can be seen using an arbitrary high quality monitor to
view the VCR's output. Also, this applies only to luminance - intensity,
not color. The color resolution is much lower and in the particular case
of SVHS vs. VHS at least, not improved over VHS since it is recorded in
exactly the same way. Also, I don't know whether this is a just noticeable
difference (JND) or percent response type of spec where the lines are really
just resolvable.
Vertical luminance resolution in the monitor or TV is determined by the video
standard (NTSC, PAL) and the quality of the monitor or TV. Specifically,
for NTSC (525 total lines for NTSC) there can be a maximum of 482 or so
active video lines and something like 580 for PAL (625 line). The remaining
lines are for blanking and sync during retrace. These are physical scanning
lines.
Vertical luminance resolution for the VCR is determined only by the number
of active video scan lines for each standard.
Factors which reduce the effective vertical resolution are CRT focus (spot
size) and stability of the interlace, and Kell factor. (See the section:
"What is Kell factor with respect to interlaced displays?".
Depending on the video standard, vertical color resolution may be less.
Depending on the video source, there will be a variety of other factors
which reduce the effective resolution horizontally and vertically.
(From Bob Myers (myers@fc.hp.com)).
The Kell factor - which has to do with the fact that we're often undersampling
an image from the standpoint of the Gospel According to St. Nyquist - IS
a factor in the reduction of vertical resolution, but interlacing plays
a part as well. This comes from at least two factors:
1. The monitor or receiver usually cannot precisely interleave the two fields.
2. More importantly, there are steps taken to reduce the interline flicker
which reduce the effective vertical resolution. This includes running the
line width of the display somewhat larger than would otherwise be the case,
and in interlaced cameras, discharging the entire screen (including the
lines from the "other" field) after every field scanned.
Interlace is particularly troublesome on moving images, where you will often
perceive momentarily "missing" details. There was a LOT of discussion
regarding the gory details of interlacing in the recent HDTV debates within
SMPTE and other groups.
Old CGA cards had RCA outputs. Usually those cards had one monochrome
monitor output and other output was composite video (usually NTSC).
This is called an RF modulator. Every VCR in the universe has one of these
and the vast majority are in self contained modules that can be reused. It
will be the silver colored metal box that has the two RF (antenna and TV)
connectors.
These are also available from surplus electronics outlets for under $5 or
as generic replacements for VCR servicing for $12 to $20.
The only connections required to make them work are a source of regulated
power - 5 to 12 V depending on model and possible s control voltage to
select output instead of pass-through mode.
(From: Tomi Holger Engdahl (then@tinasolttu.cs.hut.fi)).
VGA monitor pinout can be found at:
* http://www.hut.fi/Misc/Electronics/docs/old/vga_bd15.html
and more related links at
* http://www.hut.fi/Misc/Electronics/pc/video.html#connections
VGA signal timing details are documented at:
* http://www.hut.fi/Misc/Electronics/docs/pc/vga_timing.html
Information on how one commercial VGA to TV converter grabs a VGA signal can
be found at:
* http://www.hut.fi/Misc/Electronics/circuits/vga2tv/box800.html
Information about video signals in general can be found at:
* http://www.hut.fi/Misc/Electronics/video.html
Here are some Web sites of companies who market various video products for PCs.
* http://www.hauppauge.com/hcw/index.htm
* http://www.aimslab.com/f_products.htm
* http://www.fast-multimedia.com/fast/html/products/products.html
* http://www.tekram.com/tvcaptur.html
* http://www.miro.com/e/e2-products/products.html
* http://www.diamondmm.com/products/visualization/dtv-1100/
* http://www.matrox.com/mgaweb/mediaser.htm#mediatv
But be careful, what they say is not always the reality...
Here is an example of a homebuilt video digitizer:
* http://www.ucl.ac.uk/~ucapwas/video.html
If they are truly independent, then this is a non-trivial problem. You will
need to either:
1. Genlock the two video signals so that they are in sync before mixing.
Depending on the sources, the difficulty may range from easy to
impossible. Production video equipment will probably have the necessary
inputs and outputs. Consumer stuff probably will not. For mixing
N signals sources, N-1 will need to have genlock inputs.
If this is not possible then (assuming two sources):
2. You need a real time programmable video delay. This would typically
consist of a video A/D, dual ported frame store, readout delay timing
logic, and video D/A. Since there is no way to assure the precise phase
stability needed for PAL encoding, you would probably need to separate
the luminance and chrominance and deal with them separately.
The delay would need to be anywhere up to 1/2 frame (or 1 frame if
only one of the sources can be delayed). Not an afternoon project.
For N sources, you would need N-1 0 to full frame delay units.
Also note that commercial broadcasts will sometimes shift frame
reference when cutting between remote locations which are not genlocked.
If these sources are to be supported, you will need an automatic
adjustment scheme to maintain synchronization.
For info on the availability of commercial devices, you may want to
post to one of the video newsgroups - rec.video.production, for example.
"I'm designing graphics for a computer that is used on a the set of a
TV show. When the camera operators shoot the screen, horizontal lines
roll up and down. I assume it has something to do with the scan
rates. I know there is a small program for the Macintosh that
corrects this, but I know of nothing for the PC. Does anyone know?"
(From: Dic (dic@werple.mira.net.au)).
This depends on whether they are shooting on video or film. There are display
cards for PC which allow you to dial up the vertical output rate, which you
want to match to either 30Hz( NTSC frame rate) or 24Hz (typical film frame
rate). Multiples are fine, i.e. 60 or 48Hz respectively.
But that isn't the end of it. You may have (approximately) matched the frame
rate of the camera, but you have to also lock them together as there will be
a certain amount of drift due to slight differences in the two scan (frame)
rates. For film there are devices called a Computach or a Synclock, which
attach to the movie camera and take a video input (you can just feed it
sync from your PC card but you may need to fiddle the level or polarity).
On set, they roll the camera and adjust the shutter phase so the vertical
blanking bars on the PC fall in between movie frames. The synclock then
keeps the camera perfectly synchronized to the PC sync.
If you're shooting on video it's a bit harder. You need to genlock the video
camera to the PC, which can be awkward as the PC sync may not be quite
steady enough (directors HATE having to lock to ANYTHING).
The hardest thing to do is run several PC's in the same shot, because they
won't be scanning in sync; you can lock your camera to only one at a time.
If anyone knows of PC videocards that can be genlocked together I'd be very
interested.
We do a lot of this kind of work and at the end of the day, particularly
if there is more than one PC in shot, we record the computer graphics to
video and use Amiga monitors, because they look like PC monitors but
take video input. We use Umatic or Betacam tapes because the playback machines
can be drum locked together. Obviously though, if you need a high degree of
interactivity with the actor, this won't work too well.
The vertical blanking bar on a PC is quite fine so if they aren't in the
foreground you can usually get away with just matching the vertical rate
of the PC as close as possible to that of the video/film camera. You won't
see flicker, just a fine dark line moving up or down the picture slowly.
That is about the sum total of my experience but if anyone else has better
suggestions I'd be very interested. I have seen some TV/movies with
multiple computers in shot with no sign of flicker or blanking bars; maybe
the bars are just too fine to show up?
(From: falcon@tao.agoron.com (Tom Strano)
In my personal experience, I've found that simply setting the video mode on
a PC to 640*480, any color depth, and a 60 Hz refresh rate, results in a
very stable picture, even when taped with a cheap consumer camcorder and no
attempt at synchronization. I've done this with at least 3 different
computers, all with different monitors and video cards, and it always works
fine. Perhaps I'm just luckier than some technicians...
"I wonder if anyone could tell me a good reference on how CRT controllers
operate. Specifically, how do the HSYNC, VSYNC, BLANK, and dot clocks
interact. Or, would some kind soul like to explain it? Thanks."
I am not exactly sure what you really want but here are some simple
descriptions:
* DOT clock: the pixel clock. 1/(Pixel period).
* Hactive: the time during which video on a line is actually displayed.
- Hactive*DOTclk=#Pixels.
* Hblank: the time during which no video is displayed and the beam is being
retraced.
* Hsync: positive or negative pulse during Hblank which synchronizes the
horizontal deflection circuits of the monitor.
* Htotal: Hactive+Hblank.
* Vactive: the number of lines during which video in a frame is visible.
* Vblank: active for the number of lines during which video is not visible and
the beam is retracing to the top of the screen.
* Vsync: positive or negative pulse during Vblank which synchronizes the
vertical deflection circuits of the monitor.
* Vtotal=Totaltime=(Vactive+Vblank)*Htotal.
* Csync: Hsync combined with Vsync usually be ORing or XORing.
* Cblank: Hblank Ored with Vblank.
* Composite video: Video combined with Csync usually the video is
.7 V p-p positive-bright riding on top of .3 V negative Csync.
For RGB, some monitors will want 'sync on green' which is this
type of signal only for the green video. R and B and just the
straight video. Mono composite is this signal.
NTSC/PAL: RGB color encoded and modulated. Composite video is used
for the luminance (intensity) with the color information modulated
on a subcarrier (which is ignored by a B/W TV).
One source for info on timing specs is the data sheet for a video
DAC or RAMDAC. They will usually define all of these parameters.
(From: Rob-L (rob-l@mars.superlink.net)).
DigiKey lists 74ACT715PC-ND as "Video Synchronous Generator NEW!" It is a
20 pin DIP and costs $17.50 each for small quantities. The surface-mount
version is SC instead of the PC in the above number. You have to pay an
extra $1 for the datasheet if you want one. 1-800-DIGI-KEY is their order
line. http://www.digikey.com/ is their web address.
(From: (opal@opal.co.il)).
Try philips SAA1101.
(From: Myron Brookshire (harris.mbrooksh@ic1d.harrris.com)).
Try using the National Semiconductor LM1881 It's a 8 pin DIP that does
exactly what you need.
I think it costs @ $8.00 and you only need a couple of caps
externally.
(From: Jan Arvidsson (janarv@algonet.se)).
The EL4583C from Elantec has a dedicated HSYNC output in addition to CSYNC
and VSYNC outputs, available on the less expensive LM1881 (National). It is
of course very easy to derive a pure HSYNC signal from the CSYNC output!
Most VCRs go to their graves not because of electronics problems but because
of the death of the tape transport. Or, perhaps, because the owner was not
willing to spend the money or take the time to resuscitate (or has killed it
due to improper servicing). Of course, it might just need a 50 cent rubber
tire (but that is for another FAQ). What this means is that the tuner and
video circuitry is generally as good as the day the VCR rolled off the
assembly line.
If you have a composite monitor (probably gathering dust at this point), then
this in conjunction with the otherwise useless VCR will result in quite a nice
TV. Many CGA monitors as well as early auto-scan or multi-scan monitors have
NTSC (or possibly PAL) compatible composite inputs. Some even have built in
speakers. A set of RCA patch cables and you are all set. Since they were
designed for high resolution (at the time) computer applications, the quality
is generally excellent. (Note: I do not make the same quality claims for
modern SVGA monitors as their display is optimized for high scan rate computer
video and not CGA or NTSC). In addition, controls are usually accessible to
permit any desired degree of underscan or overscan.
It may even be possible to use the VCR's timer to turn your rig on and off
automatically! (It just requires faking out the record/cassette interlock
and locating a signal that can be used to control a power relay.
Conserve your landfills - save a VCR!
"Does anyone know about the specifications of the video and sync signals
for VGA monitors?"
Video: .7 V p-p, (more positive is brighter).
Sync: separate horizontal and vertical TTL signals. May be either polarity.
"I am trying to send VGA signals over some 180 feet of cable, I'd especially
be interested in the required line impedance of the cable."
Line impedance: 75 ohms terminated at both ends.
"Is it possible to produce a Composite Sync signal (or maybe even a
composite video signal) that could be fed into an off-the-shelf VGA
monitor, so I could use only 3 instead of 5 coaxial wires in parallel?"
RG59U 75 ohm coax is what is normally used, but you will need a good quality
cable to go 180 feet without too much signal degradation. Of course, it also
depends on what resolution and thus what video bandwidth you need and how
much dispersion (signal delay as a function of frequency) you can tolerate.
It is relatively easy to combine the H and V syncs together and then combine
these with the video (usually the green signal for 'sync-on-green') but most
low cost VGA monitors do not support this mode and you would then need to
separate the signals at the far end. You could come up with alternative
ways of combining the signals to save on cables but these will all complicate
your circuitry at the monitor end. There are multiple coax cables inside a
single sheath for just this purpose.
This is straightforward, if time consuming and tedious.
The five coaxial cables (75 ohm, RG59 typical) are wired as shown in the
table. The corresponding VGA connector pin numbers are in ().
Coax Center Coax Shield
--------------------------------------
Red Video (1) Red Return (6)
Green Video (2) Green Return (7)
Blue Video (3) Blue Return (8)
H Sync (13) Ground (5,10)
V Sync (14) Ground (5,10)
Tie pin 11 (ID0) to Ground to indicate a color monitor.
Leave pin 12 (ID1) open.
Make sure that the lengths of the cables are fairly well matched - to within
a couple of inches - to assure that the 3 color channels line up precisely.
(One foot of cable is about 1.5 to 2 ns of delay which is significant for
a 10 ns dot clock!).
Also note that you will lose your 'Plug-and-Play' capabilities without the
direct control connections to the monitor (or for monitors without these
features).
That's it!
You will wish that your fingers were about 10 times smaller than they are,
however. :-)
Pulling a fixed frequency monitor by more than a few percent will likely
be a problem. I know this is not the answer you were looking for but
getting a new inexpensive video card may be a better solution.
If not, you are looking for an adjustment called horizontal oscillator,
horizontal frequency, or horizontal hold. If you do tweak, mark everything
beforehand just in case you need to get back to the original settings.
There is some risk - changing it too far may result in damage either
immediate or down the road - I have no idea.
These are often high quality monitors and would make nice TV displays -
especially as there are many no doubt gathering dust on their way to
the dumpster!
However, these are digital (TTL) monitors with respect to the video inputs
and proper linear video amplifiers may not even be present. Therefore, you
may need to implement both the NTSC or PAL decoding as well as boosting the
signal levels to the hundred volts or so needed to drive the CRT.
The scan rate of CGA is the same as NTSC so deflection is not a problem.
For PAL (625/50) instead of NTSC, the vertical rate will need to be reduced
to 50 Hz but this should not be a problem. The horizontal scan rate is close
enough (15.625 KHz).
Similar comments apply to EGA monitors that have a compatible scan rate.
EGA represents a range of scan rates between 15.75 KHz and 21.85 KHz so
this should not be a problem.
There is no easy way to tell by just examining the monitor visually. Even
those with only a 9 pin rather than a 15 pin connector are sometimes SVGA
(e.g., Mitsubishi AUM1381 and NEC Multisync II which will do 800x600 at
56 Hz V non-interlaced and 1024x768 interlaced at 43 Hz V).
You cannot even safety test scan rates on all monitors - some will blow up
or be damaged by being driven with incorrect video.
For a monitor that you already have, posting the model number or looking
it up is really the only way to be sure of its capabilities.
Quicky tests:
1. Check the video connector. If it has a high density (VGA) 15 pin connector
then there is a greater likelihood of SVGA but not always.
2. Check the manufacturing date on the back. If it has a manufacturing date
of 1991 or later, the likelihood of it supporting SVGA is higher as
demand for VGA-only monitors was rapidly declining by this point.
3. Check the dot pitch on the CRT by examining the screen with a magnifier.
If it is really coarse, the monitor probably cannot do anything beyond VGA.
4. Become familiar with the major manufacturers and models so that you will
recognize the common SVGA models.
While not conclusive, positive results on the first 3 of these tests definitely
increases the likelihood that it supports at least some SVGA modes. Of course,
if you recognize a model number, you have dramatically increased your odds
of success - assuming it works!
The following URLs provide quick access to the general specifications of
many common PC and MAC compatible video monitors:
http://www.nashville.net/~griffin/monitor.html
http://www.hercules.com/monitors/mdb.htm
Typical question:
"I have an old mitsubishi monitor, model number C3919N, Scan rate is
15.5-23.5KHz horizontal, analog. I want to run video from my pc svga card
into this monitor. I found the correct video mode, resolution, etc. in
which it works, but have one problem. I get two perfect images displayed
on this screen."
(From: Martin Moeller (mmoeller@delphi.com)).
I have a copy of a very detailed book on using old 19" monitors for VGA:
* The Cheap VGA book
Self Published by a Michael Johnson /Esoteric Electronics
35-r Derryfield Road
Derry NH 03038
Night only Phone # is 603-434-8494
This book contains a lot of good information and advice. He also sells kits
for less than $50 (see comment below --- sam) to make the sometimes needed sync
inversion from VGA. (VGA cards invert H and V sync depending on mode to tell
the monitor what rate to go to. As far as I know only IBM ever used this.)
I have not tried his kits but the book is very good. BTW if you pay much
more than $300 for a 19' surplus monter you have been moderately had. I do
not have any other connection with this person, I just think his book is
very good if you are even thinking of using a "non-VGA" monitor with a VGA
card.
(From the Editor).
A circuit to perform the automatic sync polarity correction is shown at:
http://www.hut.fi/~then/circuits/vga2tv.html
The cost of the parts for this circuit is probably under $5 even if bought
from Radio Shack.
Note: I believe there may be a problem with the use of normal or LS TTL
for the sync buffers of this circuit due to their sourcing of current when
the input is LOW. A gate with a Low Level Input Current of less than .2 mA
should be used. (--- sam)
These are the type of displays used to view multiple video inputs
simultaneously on a single screen - security monitoring, for example.
You have two problems: compressing the signals to 1/4 screen and synchronizing
them. The straightforward (though not simple) approach is to digitize each
at 1/4 resolution into a frame buffer which is read out at NTSC rates. This
overcomes the issues of genlocking and timing of the 4 quadrants.
"I am looking for chips that do on-screen display of text and simple
graphics. I've got some information about a Philips chip PCA8516 which
seems to be a pretty nice complete chip for doing everything I want. Are
there other chips out there that do this as well?"
(From: Jack Climent (rocket5@haven.ios.com)).
When you are looking for something for the consumer marketplace, Look
toward Mt. Fuji :-).
The MB88303 from fujitsu is an "NMOS Television Display Controller" And
the NJM 22075 is a "Sync & Video SuperImposer". These two chips and very
little else form a complete on screen text & Min graphics system. Add a
uC and you are in business. Also low cost and easy to implement. Have
hardware & software someplace if needed.
(From: Winfield Hill (hill@rowland.org))
This isn't an easy thing to do, as quite a bit of electronics is required.
Fortunately, this function is needed for TV sets, VCRs etc and several
manufacturers have created custom VLSI chips to do the task, which is called
On Screen Display or OSD. For example, Phillips, SGS-Thompson, Rohm, and NEC,
etc. all make OSD chips. Some, like Motorola, include the OSD function within
a microprocessor.
I like the NEC uPD6464A chip.
Using an OSD chip, you can roll your own design (e.g. see Sept and Oct 1996
Electronics World, which uses a discontinued chip!), but it's still a
non-trivial task! One easy solution is to purchase an OSD already on a pcb,
with all the extra circuitry and C source code software. E.g. BOB-1 from
Decade Engineering in Turner, Oregon (503-743-3194). It uses the Rohm
BU5963AS chip and cost $169 each ($200 with the software).
* http://www.mindspring.com/~kjack1/scart.html
"I'm looking for a device to do resize (in horizontal direction only) of a
video signal. Basically I need a fractional decimator (in this case 2:3).
Harris has some stuff that might be useful, and Phillips has some devices
but I think they're more geared towards NTSC/PAL (data rate here is around
20 MHz, but, then again, isn't the luminance typically sampled at a pretty
high rate?). Anyway, I also know I could do it in an FPGA with bit-serial
arithmetic, but I'd rather buy something."
(From: David L. Tosh (dlt@earthlink.net)).
Check out: http://www.gennum.com/vbprofam.htm. Gennum makes several
multirate filters vor video resizing.
Inverting a video signal means doing something to both the luminance
(intensity) and chrominance (assuming a color signal). This is not totally
trivial (at least, it is more than just putting it through an op amp). You
would have to convert to baseband, strip off the sync and invert the signal,
recombine with sync, remodulate to channel 3 or 4.
If you want to also invert the colors, then you have to decode the chrominance
to RGB, invert these, reencode, recombine, etc.
There may be some shortcuts one can take but you get the picture (no pun).
Many of these are also available at the Sci.Electronics.Repair FAQ site in the
document Pinouts for Various Connectors in Real Life(tm).
Also see the connector info at:
* http://oacosf.na.astro.it/rossi/hwb/hwb.html
Note that IBM called VGA 'Video Graphics Array' probably in reference to the
video memory. However, we will use the more popular terminology since it
agrees with the naming conventions of the other PC standards.
Original VGA (31.5 KHz - 640x480)/SVGA (35-37 KHz - 800x600) 15 pin sub D:
6
1 Red (Analog) 6 Red Return 11 (ID0) GND (Color) 11. . . 1
2 Green (Analog) 7 Green Return 12 (ID1) NC (Color) . . .
3 Blue (Analog) 8 Blue Return 13 Horizontal Sync . . .
4 Reserved 9 No Connect 14 Vertical Sync . . .
5 Ground 10 Ground 15 No Connect . . .
15 10 5
Note: Monitor ID Lines ID1,ID0=NC,G for color; G,NC for Mono. ID0 only may
be used.
Mono VGA is similar using only the Green Video and Return.
(From: Bob Myers (myers@fc.hp.com)).
Note that many of the pins shown above as "no connects" (actually, these
were sometimes used as monitor ID bits by many manufacturers) are now
defined under the VESA Display Data Channel standard. This standard provides
two protocols for display ID and control, including support for the full
ACCESS.bus interface. The current definition of the "VGA" pinout per the
DDC standard is:
6
1 Red (Analog) 6 Red Return 11 Monitor ID0 (opt.) 11. . . 1
2 Green (Analog) 7 Green Return 12 Data (SDA) . . .
3 Blue (Analog) 8 Blue Return 13 Horizontal Sync . . .
4 Reserved 9 +5 VDC (frm host)* 14 Vertical Sync . . .
5 Return 10 Sync return 15 Data clock (SCL)* . . .
15 10 5
Those signals marked with an asterisk would be supplied by the host only
if the host supports the DDC2 protocol (I2C or ACCESS.bus).
(From: Bob Myers (myers@fc.hp.com)).
This defined several protocols for digital communications between a
host system and its display. DDC provides 3 different modes:
DDC1 - A unidirectional (display to host only) serial communications system
which provides basic display ID and feature support information
(including supported timings, display size, colorimetry and gamma,
etc.) to the host. This uses pin 12 on the 15-pin "VGA" connector as
a data line.
DDC2B - Adds clock (pin 15) and return (pin 11, I think - I'm at home, and
don't have the standard with me) to enable at least ID information to
be obtained via an I2C interface. I2C is a bidirectional interface,
but display control via DDC2B is not defined at this time.
DDC2AB - Full ID and control of the monitor via ACCESS.bus. As ACCESS.bus is
basically a command and protocol definition on top of the I2C
hardware interface, this uses the same lines as DDC2B.
DDC was the first and only definition of the 15-pin D-subminiature
video output connector which VESA has provided. No further definitions
on this connector will be made, as VESA is instead concentrating on the
new Enhanced Video Connector standard which is due out later this year.
This will define a completely new connector which will include support
for DDC and separate syncs as in the 15-pin D-sub, and will also include
support for audio I/O, video input, and the USB and P1394 serial interfaces.
This is pretty standard as the NEC Multisync II, Tatung CM1495, and others use
the same pinout. However, there is at least one other pinout that has been
used which is similar to the CGA pinout. Also see the document: "Pinouts
for Various Connectors in Real Life(tm)".
I used a multimeter to determine this on the VGA to 9 pin adapter for a NEC
Multisync II.
Pin 1: Red Video
Pin 2: Green Video
Pin 3: Blue Video
Pin 4: H Sync
Pin 5: V Sync
Pin 6: Red Return
Pin 7: Green Return
Pin 8: Blue Return
Pin 9: Ground
Note: IBM PGC assigns pin 4 to Composite Sync and pin 5 is a no-connect.
BTW, don't use an EGA 9 pin extension cable to connect it to VGA. While this
will work, the wires are not shielded or the wrong wires and you will get
ghosting and ringing at vertical edges. I constructed mine using proper 75
ohm coax for the RGB and H and V sync as well (though it is not needed for
the sync).
(From: Carl Mueller).
If you're sure it's a VGA monitor (not CGA or EGA, which are not compatible
with VGA), then there are two possible likely pinouts for the plug. I believe
they are both detailed in the ibm PC hardware FAQ. One possibility is the CGA
pinout, and the other is the 9-pin VGA pinout. Check the grounds to find out.
EGA - TTL (15.74-21.85 KHz) 9 pin:
1 GND 6 Secondary Green Video/Intensity
2 Secondary RED Video 7 Secondary Blue Video
3 Primary RED Video 8 H Sync TTL Positive
4 Primary GREEN Video 9 V Sync TTL Negative
5 Primary BLUE Video
CGA - TTL (15.75 KHz - 320x200 or 640x200) 9 pin:
1 GND 6 Intensity
2 Unused 7 Unused
3 RED Video 8 H Sync TTL Positive
4 GREEN Video 9 V Sync TTL Positive
5 BLUE Video
This pinout may be used by a number of Dell monitors. The connector looks
like a standard VGA/SVGA HD15 but is wired differently (for some unfathomable
reason).
(From: Chris Lawson (lawsonc@micron.net)).
Pin 1: Gnd
Pin 2: Red video
Pin 3: Gnd
Pin 4: Green video
Pin 5: Gnd
Pin 6: Gnd
Pin 7: NC
Pin 8: VSync
Pin 9: HSync
Pin 10: Blue video
Pin 11: NC
Pin 12: NC
Pin 13: NC
Pin 14: NC
Pin 15: NC
MGA - TTL (18.43 KHz - 720x350) 9 pin:
1 GND 6 Intensity
2 Unused 7 Video
3 Unused 8 H Sync TTL Positive
4 Unused 9 V Sync TTL Negative
5 Unused
Mac II - analog (35 KHz H, 66.67 Hz V - 640x480) 15 pin.
Mac II and Quadra - analog (49.7 KHz H, 74.55 Hz V - 832x624) 15 pin.
1 Red Ground 9 Blue Video
2 Red Video 10 Sense 2
3 Composite Sync 11 Ground
4 Sense 0 12 Vertical Sync
5 Green Video 13 Blue Ground
6 Green Ground 14 Ground
7 Sense 1 15 Horizontal Sync
8 Reserved (+12)
From: adams9@apple.com (Dale Adams)
Note that the Apple 16" monitor is a fixed frequency display - i.e., it
only works at one resolution and scan frequency. Here are the partculars:
resolution: 832x624
pixel clock rate: 57.2832 MHz
vertical scan rate: 75 Hz
horizontal scan rate: 49.7 kHz
Here's the pinout for the Apple DB15 video connector:
Pin Signal Description
----- ----------- ----------------------------------------
1 RED.GND Red Video Ground
2 RED.VID Red Video
3 CYSNC~ Composite Sync
4 MON.ID1 Monitor ID, Bit 1
5 GRN.VID Green Video
6 GRN.GND Green Video Ground
7 MON.ID2 Monitor ID, Bit 2
8 nc (no connection)
9 BLU.VID Blue Video
10 MON.ID3 Monitor ID, Bit 3
11 C&VSYNC.GND CSYNC & VSYNC Ground
12 VSYNC~ Vertical Sync
13 BLU.GND Blue Video Ground
14 HSYNC.GND HSYNC Ground
15 HSYNC~ Horizontal Sync
Shell CHASSIS.GND Chassis Ground
You can pretty much ignore the ID bits. You can try the following cable
pinouts to match to a VGA connector.
Mac Video DB15 VGA Connector HD15
---------------- --------------------
2 ------------------- Red Video ------------ 1
1 ------------------- Red Ground ----------- 6
9 ------------------- Blue Video ----------- 3
13 ------------------- Blue Ground ---------- 8
5 ------------------- Green Video ---------- 2
6 ------------------- Green Ground --------- 7
15 ------------------- Hsync ---------------- 13
12 ------------------- Vsync ---------------- 14
14 ------------------- Sync Ground ---------- 10
This was introduced by Sun Microsystems and is a nice compact robust
connector. Other manufacturers have copied it.
Pin 1: NC
Pin 2: NC
Pin 3: Sense 2
Pin 4: SRTN
Pin 5: CSYNC
Pin 6: NC
Pin 7: NC
Pin 8: Sense 1
Pin 9: Sense 0
Pin 10: CRTN
Pin A1: Red
Pin A2: Green
Pin A3: Blue
The following I picked off the net so I do not know the accuracy of the
resolution table.
Analog: 13W3 connector:
+----------------- * gnd
| +------------- * vertical sync
| | +--------- sense 2
| | | +----- sense common (gnd)
| | | | +- composite sync
| | | | |
| | | | | grey
red | | | | | green blue
| 1o 2o 3o 4o 5o | |
(O) (O) (O)
6o 7o 8o 9o 10o
| | | | |
| | | | +--- composite common (gnd)
| | | +------- sense 0
| | +----------- sense 1
| +--------------- * gnd
+------------------- * horizontal sync
* May be NC. My spies tell me Sun considers these obsolete.
The green video input is used by grayscale monitors.
Sense table - 1=nc, 0=strap to gnd
Sense Type/scan rate
-------------------------------------------
0 TBD (?))
1 Reserved
2 1280x1024, 76Hz
3 1152x900, 66Hz
4 1152x900, 76Hz, 19"
5 Reserved
6 1152x900, 76Hz, 16 or 17"
7 Nothing (no monitor connected)
(From: Rob Myers (myer3812@nova.gmi.edu)).
I have the pinouts for the RGB connectors on newer Sony monitors
(specifically, the PVM-2030 and PVM-2530 Profeel Pro monitors). These pinouts
are directly from the owner's manual. The connector used is a DB25 female.
High state = 5V (open)
Low state = 0V (short to ground)
Note On Pins 3,4,5,6,11:
If pin 9 is high/open (Analog RGB mode) then .7Vpp, 75 ohm signals must
be input to these pins. Pins 1 and 25 are not used.
If pin 9 is low (Digital RGB mode) then TTL signals must be input to
these pins. Pins 1 and 25 are only used in this mode.
Pin Signal Descr
---------------------------------------------------------------
1 IBM Select High: IBM mode (RGBI)
Low: 3 Bit TTL (RGB)
2 Audio Select High: Audio input from pin 13
Low: Audio input from LINE A/B/VTR jacks
3 HSync/CSync Horizontal or Composite Sync, Negative Pol.
4 Blue Input Video Inputs: Positive Pol.
5 Green Input (Sync on green optional in analog mode)
6 Red Input
7 NC
8 NC
9 Analog/Digital High: Analog mode
Low: Digital mode
10 RGB/Normal High: RGB input selected
Low: LINE A/B/VTR input selected
11 VSync Vertical Sync, Negative Pol.
12 Blanking High: Video input from RGB input only
Low: LINE A/B/VTR signal is superimposed over
signal from RGB input
13 Audio Input -5 dB / 100% mod.
14 NC
15-24 Ground
25 intensity Positive Pol.
These monitors are regular NTSC monitors, but I'm sure they can be
connected to computers the same way I connected the KX-2501... using a
simple buffer circuit and special video drivers. Another possibility is
to build a component-to-RGB converter for really high quality DVD
playback (better than S-Video)... the blanking feature seems interesting
but the RGB source would have to be synchronized with the composite
source. I think the KX's/XBR's have the blanking input, too.
The Sony RGB Multi Input pinout is also valid for the KV-25XBR; it should also
work with the KV-20XBR and KX-1901, and I know it works with a KX-2501. (The
KX series monitors are the original Sony Profeel monitors from about 1983, and
they are very common.)
A female 34-pin floppy connector will mate with the Sony connector just fine.
I was able to use the analog RGB input on a KX-2501 to display VGA PC video
using a sync level converter circuit and drivers from:
http://www.hut.fi/Misc/Electronics/circuits/vga2rgbs.html.
(From: Yves DELAY (yves.delay@imag.fr)).
I am trying to connect a Silicon Graphics (SGI) 17" screen display to an SGI
Octane CPU. I would like to build my own HD15 to 13W3 cable.
The monitor is standard SVGA with the VESA Display Data Channel (DDC) and
works fine on a PC.
SGI OCTANE CPU video pinout (13W3):
A1 Red (analog)
A2 Green (analog)
A3 Blue (analog)
1 Monitor ID bit 3 (TTL)
2 Monitor ID bit 0 (TTL)
3 Composite sync (active low), TTL
4 Horizontal drive (active high), TTL
5 Vertical drive (active high), TTL
6 Monitor ID bit 1 (TTL)
7 Monitor ID bit 2 (TTL)
8 Gnd
9 Gnd
10 Gnd
Below is the pinout of the SGI 13W3 to HD15 cable, part number: 018-0500-001,
Rev. E VIST 9717, obtained after a phone call to the SGI hotline.
Signal SGI OCTANE (13W3) Monitor: GDM-17E21 (HD15 male)
----------------------------------------------------------------------------
Red A1 1 Red
Red Gnd A1 Gnd 6 Red Gnd
Green A2 2 Green (+ composite sync)
Green Gnd A2 Gnd 7 Green Gnd
Blue A3 3 Blue
Blue Gnd A3 Gnd 8 Blue Gnd
Pins 6, 7, and 8 tied together, along
with both connectors metallic shell
and cable shield.
ID3 (1): not used
ID0 (2), ID2 (7), and
Gnd (8), all tied together).
Other pins: not used