Turning these video signals into VGA - Page 1
Forum section: electronics / projects

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 26, 2016, 03:07:43 am
content: Hi!I'm trying to convert an old HP 1662AS Logic Analyzer/Oscilloscope from CRT display to an LCD display. The video connection to the CRT module has HSYNC, VSYNC and Video channels (service manualhttp://www.doe.carleton.ca/~nagui/labequip/la/1663C%20Service%20Guide.pdf).I made measurements of the signals which can be seen here:https://keepdevelopingprojects.wordpress.com/2016/01/25/project-crt-oscilloscope-lcd-mod-motivation/. No need to read, you can just look at the screen shots.My plan was to use an FPGA/fast(~70MHz) microcontroller to read the current video signals and then output VGA signals. However, I was wondering if anyone could see an easier way to do this?Could I just change the voltage levels and do some buffering and then send it straight to a VGA display? I know that VGA normally has a 31.469kHz horizontal frequency whereas these signals have a 25kHz horizontal frequency, so I guess not.Any insights would be great.Matt

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 26, 2016, 03:12:17 am
content: I believe you can buy off the shelf small converters from composite to HDMI or to RGB.But why wouldn't you simply get an LCD display that accepts composite and just eliminate the need for any kind of converter?

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 26, 2016, 03:21:00 am
content: Is this a composite signal? If it was, then wouldn't it only have one line? Instead of HSYNC, VSYNC and Video...

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 26, 2016, 03:23:04 am
content: It is essentially trivial to insert the H-sync and V-sync into the video signal to create "composite".It could be as easy as a couple of 5-cent resistors.

author: Ian.M
author_rank: Super Contributor
timestamp: January 26, 2016, 03:42:47 am
content: Some arcade games used to use a 25KHz scanrate. There are a few off-the-shelf VGA converters than can handle it, and if you are lucky, you will find one that's plug in & go with the signals you have.

author: miguelvp
author_rank: Super Contributor
timestamp: January 26, 2016, 04:35:34 am
content: Silly question, did you try to feed the HSync, VSync and the video to for example the red channel of a VGA monitor? (Edit: don't do that, just read it and saw you have 3.5V on your video signal, so you need to adjust that to not exceed 0.7V)As long as the HSync and VSync are at TTL/CMOS levels (5V or 3.3V) and your video is within the 0-0.7V it should be fine for the monitor, other than it might not support it and it wont lock to the signal.Edit: for what I read you are getting 3.5V on the video signal. So maybe not plug it directly you have to bring down that video signal to 0.7V max.Edit2: but it's unclear, you have your probes set to 10x so does that mean your video signal is from 0 to 0.35V? the scope captures show 1.25V or so with 10X so 0.125V so that's not clear, because they are pretty zoomed out.Your timings seem to match 1/3 of this resolution on the vertical:http://tinyvga.com/vga-timing/1600x1200@60HzIf you divide the Horizontal timings by 3 as well that would be an 18MHz pixel clock (~55.56ns per pixel)I was doing a project driving a VGA screen with an MCU, I can play with plugin in those values and see if my VGA LCD panel locks to something like 533x400(visible 720x417 total including the front, back and pulse signals) which seems it will match your timings (other than the sync pulses are positive while yours are negative, but I can change those on my module as well).For example these are the values I used for 800x600@60Hzusing the values in here:http://tinyvga.com/vga-timing/800x600@60HzMore info on my project here:https://www.eevblog.com/forum/projects/no-bitbanging-necessary-or-how-to-drive-a-vga-monitor-on-a-psoc-5lp-programmabl/I'll test it and report back to see if it locks.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 26, 2016, 04:40:12 am
content: Green is the traditional combined sync channel.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 26, 2016, 05:16:31 am
content: @Richard CrowleyOh I see, that's a good idea. Ideally I would want the signal in VGA format, but I'll bare that approach in mind.@miguelvpThat is very interesting. Those timing specs are indeed 3 times what I have. The difference is that the datasheet specifies 500 horizontal points which would give a pixel clock of approx 17.2Mhz.Of course I could simply invert the HSYNC and VSYNC pulses if necessary.

author: johnwa
author_rank: Frequent Contributor
timestamp: January 26, 2016, 05:40:21 am
content: Quote from: miguelvp on January 26, 2016, 04:35:34 amYes, the OP basically has an analogue video signal with a 25kHz horizontal scan rate. Pretty much any monitor should be capable of displaying it fairly easily, provided that it can sync that low. Old CRT monitors sometimes had the sync range specified in the manual; something like 30-66kHz might be typical. LCD monitors have less technical constraints than CRTs, but are usually still made to only accept a certain range - some may be more forgiving than others.I once had to fix a machine tool control with a failed monitor. It appeared to have a dead tube, and there was a long lead time on a replacement. I can't remember the horizontal sync frequency, but it would have been CGA or EGA (15 or 22kHz). After trying almost every LCD monitor in the office, I eventually found one that would lock to the signal, which got the machine up and running again until we could get a proper replacement. So, it appears that at least some LCD monitors will handle these low sync frequencies.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 26, 2016, 05:41:25 am
content: Actually, the datasheet saysQuoteI originally took that to mean that the whole display way 500x240, but actually it looks like just the Waveform region is 500x240. It looks to me like there are more like 400 lines. So maybe we are looking at 533x400 like you say

author: miguelvp
author_rank: Super Contributor
timestamp: January 26, 2016, 05:44:46 am
content: Well I did plugged in the following valuesand on the scope it looks good.I did trigger on Ext with the VSync and display HSync on Chan 1 and Red on Chan 2But the display says it's out of range so no joy.Quote from: Alex Eisenhut on January 26, 2016, 04:40:12 amI know, I'm not trying to combine the composite sync into the green channel, the OP has access to the HSync and VSync so no need to do that.

author: miguelvp
author_rank: Super Contributor
timestamp: January 26, 2016, 05:50:00 am
content: Quote from: MattHollands on January 26, 2016, 05:41:25 amVideo displays are usually, actually always, divisible by 8 on both directions. Maybe it's 536 visible. I'll play with the numbers a bit.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 26, 2016, 05:53:29 am
content: I know originally I stated that the voltages were between 0-350mv (on 10:1 probes uncompensated). I think I must've been reading off of the wrong scale which is embarrassing. I've just checked and the voltage varies between 0 and 1.298V on a 1:1 probe.

author: miguelvp
author_rank: Super Contributor
timestamp: January 26, 2016, 06:06:45 am
content: Since the horizontal timing is really 720 clock pixels, could it be that it's displaying 640x400?is there anyway you could show the scope traces for a single scan line? with the Hsync so we can see the front porch, back porch and pulse in relation to the displayed pixels?and also add a close up picture of the screen, that might help.Edit: maybe if you could manage to get a screen capture into the floppy disc? I'll look to see if google can help on that as well.

author: miguelvp
author_rank: Super Contributor
timestamp: January 26, 2016, 06:22:16 am
content: Quote from: MattHollands on January 26, 2016, 05:53:29 amMaybe start with just hooking up the HSync and VSync If they are below 5V to a VGA monitor and see if it locks (with no video fed to it)From my findings it seems the monitor controllers don't actually care if the pulses are positive or negative. I think they simplified things and just care about the pulse and not the polarity of the standard.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 26, 2016, 06:53:33 am
content: Ok here is a picture of one line and also of the whole display. I think if you zoom in you can resolve the lines. I counted a few lines and extrapolated (using a tape measure!) and got around 390 lines, so 400 is easily within error margins.I don't think I have much chance of getting a floppy disk quickly.

author: miguelvp
author_rank: Super Contributor
timestamp: January 26, 2016, 04:10:41 pm
content: I ran out of time last night.I'll analyze the picture after work today.Edit: looks like it's a line going across the Analyzer/Configuration Print/Run buttons.Huge horizontal Back Porch compared to your average video format.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 27, 2016, 06:39:57 am
content: I'm going to try and track down a VGA display to test the HSYNC/VSYNC signals to see if it locks on.

author: miguelvp
author_rank: Super Contributor
timestamp: January 27, 2016, 06:51:11 am
content: Sorry I'm still trying to analyze the image to get the pixel clock and the horizontal timings based on your scope captures, but with the aliasing on the scope image it's hard to do.My hope was to reproduce your video signal and see that it locks on my displays.Maybe even if it doesn't lock it might be as simple as in changing the horizontal back porch and the amplitude of the video signal by dividing it by two.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 27, 2016, 07:04:14 am
content: No worries at all, thank you so much for your help so far.I understand how you could change the video signal amplitude, but how would you change the back porch?Would you insert an FPGA/uC in the signal path and effectively buffer the signals to stretch the visible region over a larger region of the horizontal period?

author: miguelvp
author_rank: Super Contributor
timestamp: January 27, 2016, 07:43:09 am
content: Quote from: MattHollands on January 27, 2016, 07:04:14 amYes, you could do a PLL to sync the HSync with the MCU/FPGA/CPLD and force the back porch to be smaller or in other words trim it, if that helps sync with what a VGA controller can sync to, therefore extending what the visible region is but clamped to 0V.Might not be that simple but the alternative is to capture the analog signal and do an upconversion to VGA, that would be more costly.Then again as johnwa mentioned, he did find and LCD monitor that will lock to lower frequency sync signals.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 28, 2016, 04:06:59 am
content: Ok, managed to get hold of a VGA monitor and test with it (Just HSYNC, VSYNC and GND). When I turn on the CRT the message changes from "Cable not connected" to "Input not supported", which suggests that it is detecting something but is not happy with the signal, I assume the 25kHz part.Looks like I'm going to have to include some kind of buffer in the middle to change the clock...Would you expect something like a Teensy 3.2 running at 72MHz to be able to handle this? Or should I look to an FPGA or similar?

author: miguelvp
author_rank: Super Contributor
timestamp: January 28, 2016, 05:29:29 am
content: The problem will be buffering the analog data, that will require a video ADC and a DAC to drive it at a different frequency.Sorry I didn't have time to deconstruct your signal yet. Been very busy the last two days.

author: miguelvp
author_rank: Super Contributor
timestamp: January 28, 2016, 07:36:07 am
content: So I took your image and tried to figure out the resolution, I'm getting some weird valuesHorizfront 16sync 46back 104vis 416(total 582)pixel clock 14,550,000 HzThe closer I can get my pixel clock is 14.5 MHzStill out of range but I can play now with the horizontal back porch but I doubt is going to lock.here is compared to your signal.There is also another possibility, getting one of those retro gaming upscalers but not sure if they will work with your setup and resolution.http://www.amazon.com/gp/product/B00988GMLGThey can convert 15KHz signals to HDMI but not sure if it could upscale your signal. Also I don't know what they have inside and if you could change and program it, plus you will have to feed your video signal converted to SCART levels to all three RGB inputs.Is there a possibility you could take a scope capture of the VSync with respect of the HSync so I can fine try to replicate the vertical front,back porch and pulse?Edit, each of the dashes is really every three pixels, I did the same with the Image33.jpg to count the pixels, but it's too big on resolution to embed in the post.

author: Ian.M
author_rank: Super Contributor
timestamp: January 28, 2016, 08:06:58 am
content: Wrong upscaler. The retro arcade machine community has upscalers that can handle their medium rez. (25KHz Hscan, 60Hz Vscan) consoles. Google:25KHz JAMMA converter VGAIf you can find the 3 bit digital signal responsible for those brightness levels, you could remap it into RGB and tweak the pallete to your own tastes. I'm thinking a fast 3 to 8 line decoder driving analog switches to select from a bank of 24 presets to provide an analog RGB colour to replace each brightness level.

author: miguelvp
author_rank: Super Contributor
timestamp: January 28, 2016, 08:13:31 am
content: Quote from: Ian.M on January 28, 2016, 08:06:58 amActually the price of those is not too bad, but with that humongous back porch I wonder if it will work:http://www.ebay.com/itm/Gonbes-GBS-8200-CGA-15kHz-EGA-25kHz-Arcade-JAMMA-PCB-to-VGA-Video-Converter-/111462780792

author: macboy
author_rank: Super Contributor
timestamp: January 28, 2016, 02:51:48 pm
content: Quote from: miguelvp on January 28, 2016, 08:13:31 amIt "Supports image position control & image zoom control", so in theory you can adjust for different porch durations. Whether the range of those controls is sufficient is unknown. Hopefully when combined with the monitor's own image postion and size adjustments, it can be dialed in.

author: miguelvp
author_rank: Super Contributor
timestamp: January 29, 2016, 04:41:18 pm
content: @OPQuote from: miguelvp on January 28, 2016, 07:36:07 amWith that information I can replicate your signal and see what can be done to lock it.Also be careful when the time comes to replace the tube and it's power supply, but for the sound of things it seems you are aware of the HV dangers in there, but never hurts to point it out for others reading the thread.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 29, 2016, 11:21:56 pm
content: I'll get a VSYNC and HSYNC picture tonight! Sorry, had a very busy couple of days!

author: miguelvp
author_rank: Super Contributor
timestamp: January 30, 2016, 01:45:27 am
content: Take your time, wife is taking me out for dinner, or is it the other way around? I'm never sure

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 30, 2016, 04:29:38 am
content: Ok I've taken images of the VSYNC and HSYNC together.I've taken images at multiple time-bases so you can see it on different scales. The timebase is included in the name of the file. Of course blue is VSYNC and red is HSYNC.Have a good evening!

author: miguelvp
author_rank: Super Contributor
timestamp: January 30, 2016, 05:35:28 am
content: Thanks, it seems the video is interlaced so you have even and odd fields.I'll take a look at them tomorrow in more detail.Edit: not interlaced, not sure why I thought that, I guess I'm not too used to white wine

author: miguelvp
author_rank: Super Contributor
timestamp: January 30, 2016, 07:29:21 pm
content: I don't know what I was thinking.The HSync vs VSync doesn't give us nothing new other than the vertical pulse, sorry for asking that and wasting your time.What it would be useful to find the vertical front and back porch, would be showing the video signal versus the VSync as this:That shows the front porch to be 2 lines, the sync as 3 lines (which is what you showed) and the back porch to be 12 lines.

author: MattHollands
author_rank: Frequent Contributor
timestamp: January 31, 2016, 03:45:01 am
content: No worries, it doesn't take long to capture some waveforms!Here is VSYNC-VIDEO at a few timebases.

author: miguelvp
author_rank: Super Contributor
timestamp: January 31, 2016, 05:26:16 am
content: Well, at least I think I have your video reproduced, well as close as I could get since I can't get the exact pixel clock.Here is my result based on your VSync vs Video:Your signal is:Screen refresh rate: 60Hz (Edit: correction the refresh rate is really 59.952 Hz)Vertical refresh: 25.000kHzPixel freq: 14.550 MHzHorizontal timing (line):Polarity of horizontal sync pulse is negativeVisible area: 456 pixelsFront porch: 16 pixelsSync pulse: 46 pixelsBack porch: 64 pixelsWhole line: 582 pixelsVertical timing (frame):Polarity of vertical sync pulse is negativeVisible area: 378 linesFront porch: 11 linesSync pulse: 3 linesBack porch: 25 linesWhole frame: 417 linesHere are the settings for my programable module:I'm going to try to hook it up to my TV that has VGA input (you shouldn't do that because the voltage of your video signal is way beyond 0.7v)Edit: my thought is that TVs do support legacy NTSC signals so there are higher chances that it would sync.Also I'm going to try if like Richard mentioned earlier if I can make a composite signal out of this, maybe based on an Analog Devices RGB to NTSC/PAL Encoder AD724 if I can find one out on ebay since I would think it's obsolete, but there are plenty of VGA to composite adapters out there available for very cheap.I know composite is not ideal but since you are really just doing black and white it might be not too bad and finding an LCD that takes composite in is easy.Also I have co-workers that have old cabinets and they might have that JAMA converter, I'll ask around to see what it makes out of this signal.I'm surprised the visible resolution is just 456x378, can you confirm those values?

author: miguelvp
author_rank: Super Contributor
timestamp: January 31, 2016, 05:50:26 am
content: I just noticed the pixel clock is very close to NTSC 14.318180 MHzI'm going to see what horizontal values will be needed for that pixel clock frequency to stay at 25kHz and leave the vertical alone.It's more likely to be that frequency than the 14.550 MHz I measured visually.Edit: Nah, that gives me 572 pixels for the whole horizontal line or just 456 visible pixels, so I think the 14.550 MHz is the right pixel clock.

author: miguelvp
author_rank: Super Contributor
timestamp: January 31, 2016, 06:23:29 am
content: Well, I did hook it up to the TV VGA input and:That's my little board on the lower left of the image.It doesn't give me resolution information and I'm just displaying white at the moment.Tomorrow I'll see if I can put a more advanced version of my project with these values and some text to see if there is any distortion or glitching.The good thing is that at least a small LCD TV might do the job for you as long as you can divide your video input signal by 2 so is within tolerance.Edit: at least on a US LCD TV, but maybe they all support PAL/NTSC/SECAM as far as timing signals go via the VGA connector.

author: miguelvp
author_rank: Super Contributor
timestamp: January 31, 2016, 06:45:55 am
content: More on the 456x378 visible resolution.If the device character set uses 8x9 glyph sprites, it will yield to a text resolution of exactly 57 by 42 characters, which seems to be consistent with the picture you posted if you zoom in:Edit: It seems the sprites are 6x9 that will be 76 by 42 characters, I think that is more likely, but the 456x378 resolution seems to hold.

author: miguelvp
author_rank: Super Contributor
timestamp: January 31, 2016, 08:51:30 pm
content: So I did use a version of my code that displays the character set and keeps on inverting one character every frame, so it inverts 60 characters per second.I'm using some graphic sprites to separate the characters but those take a full 8x16 block of pixels the same as the characters do.On the vertical i'm dividing the full resolution by 2 so in essence every character takes an 8x16 pixelOn the horizontal it's using 8 pixels per character so we expect 57 of them for the full 456 visible pixels, and we do get those.On the vertical however I was expecting 378/16 or 23.625 characters, but I'm only seeing 22. I can go through the TV menu and change the vertical position and I can see the 26 missing pixels, but my TV doesn't let me adjust the height to see all the frame.In short, out of the 456x378 visible in the signal, I can only get 456x352 to display on my particular TV as seen here:If I was using the original signal, it will mean that 3 lines of text would be missing since your characters are 9 pixels high, but maybe your TV can adjust the horizontal scaling of a VGA signal or you can change the horizontal scaling on your HP 1662As Logic Analyzer/Oscilloscope.But the good news is that your signal locks into an LCD TV, now to find one that matches your screen dimensions not the 40" I'm usingAlso consider the Composite conversion, there are a lot of LCD panels for back-up camera systems that take Composite and they are up to 8 inch LCD panels diagonally.What is the diagonal dimension of your screen?Edit: also if you have a small LCD TV around that has VGA input and a VGA cable and you just wire the Ground, HSync and VSync but not the video you should be able to see if that TV will lock into the signal.Then you can use a resistor divider with 75ohm termination of your video signal and connect that to all three RGB inputs of the VGA connector and you should be able to see the screen.

author: miguelvp
author_rank: Super Contributor
timestamp: February 02, 2016, 02:15:22 am
content: @MattHollandsDo you think using an LCD TV would be enough for your needs or do you want me to test this signal with converting it to composite (just some resistors and a electrolytic cap) will do.Also I can look to see if anyone around work has a JAMA converter and test it.Also did you try to put the HSync, VSync with no video to an LCD TV to see if you get it to sync?And the diagonal dimension of your CRT and aspect ratio (probably 4:3) to look for a suitable panel.

author: MattHollands
author_rank: Frequent Contributor
timestamp: February 02, 2016, 03:04:51 am
content: Great to see that the signal is working for you!I actually would like to mount the screen inside the original case, where the CRT currently is. Ideally I would also add a "VGA out" port where I could attach an external monitor too.I assume it's pretty easy to get a composite to VGA converter? In which case I could convert it to composite and then convert that to VGA which could drive any screen?I did put the HSYNC, VSYNC signals without Video into a PC monitor, but not a TV.

author: miguelvp
author_rank: Super Contributor
timestamp: February 02, 2016, 03:32:17 am
content: I assumed you wanted it inside, that's why I was asking for the diagonal size of the CRT in inches.There are some options:1) Find a small LCD TV that has VGA input and that fits inside and bring the voltage of the video signal so it doesn't go over 0.7V with a 75Ohm termination this won't allow for an external VGA connector unless it's hooked into a larger LCD TV that has VGA input.2) Find a small LCD monitor that fits inside that takes Composite as an input (like the cheap rear view camera kit that they sellfor backing up your car). You'll have to find the right value resistors and electrolytic cap so that the Composite signal is compliant.This won't allow an external VGA monitor either unless it's an LCD TV that has Composite input.3) Use the JAMA board to scan convert your signal (after bringing the video voltage down to 0.7V) Then you can find an LCD panel with VGA controller that will fit where the CRT is and allows to put a VGA output that will work on any VGA LCD monitor. That is if the JAMA board can lock into your signal and upconvert properly.The cheaper options are the LCD TV with VGA or Composite inputs that matches the dimensions of your CRT.

author: MattHollands
author_rank: Frequent Contributor
timestamp: February 02, 2016, 04:55:17 am
content: Sorry, I missed that part of your response. The display is currently ~9", however I would be happy with 9, 8 or 7" because I plan to make some modifications to the case too.I'm tempted by the Jamma board because it seems very flexible. It's also not a huge expenditure, so perhaps I'll give it a shot. Seeing as your LCD TV managed to lock onto the signal, it seems quite probable to me that the Jamma board will be able to lock on, seeing as it's designed to be flexible with the input signal.I'll probably order it tomorrow unless I change my mind before then.

author: miguelvp
author_rank: Super Contributor
timestamp: February 02, 2016, 04:59:44 am
content: Cool, let me know how it goesEdit: still take care of that video voltage of yours 1.3V might be outside of the JAMA board specs.

author: MattHollands
author_rank: Frequent Contributor
timestamp: February 02, 2016, 05:16:45 am
content: Just looking at the datasheet, it appears that the board requires 2A, which is a lot and I'm not totally certain if I will be able to extract that from the oscilloscope power supply.Perhaps I should try the composite signal first.Just going back to your original option 2 posts ago: Isn't option 1 the same as what I tried with my monitor where I connected the VSYNC and HSYNC signals and it didn't lcok? Are you suggesting I search for a monitor that will lock onto these signals?

author: TheSteve
author_rank: Unknown
timestamp: February 02, 2016, 05:21:31 am
content: I have been able to use one of those jamma boards to convert the video out from an HP8921A service monitor to VGA. It uses something like 300mAh when running, I've never seen anything close to 2 amps. The HP8921A has a 19 kHz video out on a single connector so I also use an LM1881 to separate the sync signal.

author: miguelvp
author_rank: Super Contributor
timestamp: February 02, 2016, 05:22:16 am
content: Option 1 would be looking for a 9" LCD "TV" with VGA input, not a computer monitor.Apparently TVs have the hardware for NTSC like signals so chances are that they will lock.Option 2 is one of those back-up car rear cameras and displays I'll look around but usually the LCD part of the system takes Composite video that the rear camera supplies. Since your signal is black and white, you don't need to care much about producing a color burst on the composite video.I'll look for a schematic on how to get composite from this signal.

author: miguelvp
author_rank: Super Contributor
timestamp: February 02, 2016, 06:33:21 am
content: For option 2 here is a simple diagram of VGA to Composite B&Whttp://www.geocities.ws/podernixie/htpc/cables-en.html#vgavideoSince you don't have RGB at 0.7V you need to bring that 1.3V value to the Composite level.I'm not too familiar with the Composite signal but I think the max voltage is about 1V so you'll need a voltage divider to bring it within that 1V.Someone please step in if I get this wrong.Since the video signal has to be 75 Ohm terminated I would use a 75 Ohm resistor from your video signal to ground after passing the signal through a 25 Ohm resistor. I think that will put you in the 1.0 volt range.If it was for VGA I would use a 75 Ohm resistor to ground after passing the signal through a 75 Ohm resistor halving your video voltage.As for the LCD Composite monitors is a gamble if they will work but there are plenty on Ebay:http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=9+inch+backup+camera+system&_sop=15Those are full systems with the camera, remote etc, but you just want the display that takes Composite in.I'll search if I can find an LCD TV with VGA input that is just 9 inches for option 1.Option 1 is probably a gamble too:I don't know if this little car monitors can deal with NTSC signals:http://www.dx.com/p/9-digital-car-monitor-displayer-w-touch-keys-vga-hdmi-av-black-411613#.VrBN7xUrKUkhttp://www.ebay.com/itm/Portable-8-inch-TFT-LCD-4-3-Color-Monitor-Screen-Display-VGA-BNC-AV-Fo-PC-CCTV/271308397540There are a trillion of them those are just two examples, but hard to tell if they will lock into your signal via the VGA or Composite connectors. But both will work with the JAMA board I would think.

author: MattHollands
author_rank: Frequent Contributor
timestamp: February 03, 2016, 05:26:04 am
content: Ok thanks for all of that miguelvp!Based off of TheSteve's input I've gone ahead and ordered the Jamma board from ebay. Should arrive on the 9th of feb!

author: miguelvp
author_rank: Super Contributor
timestamp: February 03, 2016, 05:49:07 am
content: I'm thinking on getting one myself for my older video game consoles.Btw people are hacking at it to improve it:http://shmups.system11.org/viewtopic.php?f=6&t=52172Lots of datasheets on that link.Other links:https://ianstedman.wordpress.com/gbs-82xx-experiments/https://ianstedman.wordpress.com/2015/01/25/gbs-82xx-experiments-part-2/BTW I can't take credit for that board, it was Ian.M that suggested it.I would have tried the SCART to HDMI but it seems this one is more flexible.Did you get the GBS-8220? that has dual VGA outputs.Edit: but if you didn't it doesn't matter, it has a VGA connector and associated pins as well, maybe with some transistors you can duplicate the output anyways without loosing driver power to either screen. The linear regulator on the 8220 has less ripple too, but not sure how bad the switching supply could be.Other than that they are both identical.

author: MattHollands
author_rank: Frequent Contributor
timestamp: February 03, 2016, 10:35:33 pm
content: I think I got the one with two VGAs, but its from ebay so can't be sure! Just gotta wait for delivery now.

author: miguelvp
author_rank: Super Contributor
timestamp: February 03, 2016, 10:55:33 pm
content: If you want to fine tune it, you should download the documents from that "GBS 8200/8220 CFW Project",He has a google drive with all kinds of datasheets and programming guides:https://drive.google.com/folderview?id=0B9y2RH4Lb3MZLUYtWGFOMUFVdlE&usp=sharing

author: miguelvp
author_rank: Super Contributor
timestamp: February 04, 2016, 08:44:56 am
content: Well, after reading the documentation and all that jazz and since I do have several retro game consoles I did a search and found the dual header (GBS-8220) at Amazon, so I got one that should be here in a couple of days (no I didn't pay extra, actually free shipping because my wife is an Amazon Prime member).It's pretty cheap in there so I just couldn't help myself:http://www.amazon.com/Andoer-Portable-GBS-8220-Definition-Converter/dp/B00XKWX0SYSorry I didn't find this before hand.The reason I did get it is because if you look closely on the chip, it does have digital input OR output (not both) for maybe doing HDMI out as well since VGA on TVs are pretty much phasing out and the composite video from game consoles do suck a lot.If I get mine before yours I'll see if it works with my repro signal.One thing I did find on video reviews etc is that the menu usually defaults to Chinese. If that is the case for you, press the Menu button and select option 4, that's the language selection and you should see English on that submenu as option 1.Also by looking at the input voltages you might not need to alter the output voltage at all, specially since they have pots to adjust the level for all red green an blue channels which you probably want to drive all three with your video signal and adjust them to get your preferred foreground color.

author: miguelvp
author_rank: Super Contributor
timestamp: February 06, 2016, 06:30:26 am
content: Well, gotta love Amazon, got my board already.Good news/Bad news.Bad news is that out of the box applying the signal similar to yours I can't get it to lock.Good news, well not that good, is that I can see something on the screen.I think it's because for the 25KHz signal it needs to use the RGBS, meaning that the HSync and VSync have to be combined.Also since there is plenty of documentation maybe we can coerce the video processor (TVIA TrueView 5725) to work with your signal since we have access to all that documentation on that google drive.Since I can reproduce your signal and I have the board I can keep on helping but I hope I didn't make you waste ~$30 and sorry if you paid more.

author: Ian.M
author_rank: Super Contributor
timestamp: February 06, 2016, 09:19:16 am
content: The first thing I'd try would be XORing the H and V sync signals to get what should closely resemble a correct C sync signal. As they don't go all the way to 5V, use 74HCT or real TTL. One gate from a 74HCT86 or 74LS86 should do the job.

author: MattHollands
author_rank: Frequent Contributor
timestamp: February 07, 2016, 06:05:21 am
content: Hmm mine still hasn't arrived! That's annoying. No worries, I'm sure we will figure out a way to get this to work.I'll check my components to see if I have any HCT or LS series. I feel like I won't because I'm studying abroad for the year so don't have all of my kit with me

author: Ian.M
author_rank: Super Contributor
timestamp: February 07, 2016, 07:33:00 am
content: An XOR can be built from four NAND gates, so you could also use all the gates of a 74LS00 or 74HCT00.Other 'flavours' of CMOS logic would probably work, but your sync pulse high level is only about 4V which is a bit marginal for a logic '1' in most families if powered from 5V.

author: miguelvp
author_rank: Super Contributor
timestamp: February 07, 2016, 08:01:41 am
content: This link I think it will be of use, posting it here for future reference:https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vgaLook at the combined sync section.

author: Ian.M
author_rank: Super Contributor
timestamp: February 07, 2016, 08:22:08 am
content: @miguel: *EXCELLENT* find!

author: MattHollands
author_rank: Frequent Contributor
timestamp: February 09, 2016, 07:32:49 am
content: My board came today! Turns out it's the version with only one vga output. I'll try to find some time in the next couple of days to experiment.QuoteSorry for being slow. How can I find whether or not the voltages need adjusting?

author: miguelvp
author_rank: Super Contributor
timestamp: February 11, 2016, 06:51:45 am
content: It's ok, I'm taking a trip to Spain in a couple of days and I won't be back for over a week after that. I'll take my tablet but I won't be able to look at this for another two weeks.But I'll keep my eye on the thread.

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 31, 2024, 09:42:03 am
content: Quote from: miguelvp on February 07, 2016, 08:01:41 amDoes anybody has a copy or an update link ?Thank you, Albert

author: squadchannel
author_rank: Frequent Contributor
timestamp: October 31, 2024, 09:57:10 am
content: Our waybackmachine!https://web.archive.org/web/20220127084244/https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vga