TMS9929 (Sega etc.) display direct to modern TV!

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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby arjoll on Tue Mar 19, 2013 5:16 pm

natshaw wrote:They store them on foil/polystyrene and don't care if the legs miss the foil, and they don't use static bags nor straps.

I very much doubt there would be an issue. Most linear ICs are fine, I'd only be worried about the likes of 4000B CMOS. I'd have no hesitation handling the pins of an average op-amp like the TL07x series.

natshaw wrote:My circuit sim shows the 4MHz-rated CA3140 have slew rate issues over a couple Mhz, resulting in poor gain - is that how opamps are rated - max Mhz is only for unity gain? I might have to go for the big brother 15MHz CA3130, or something else, feels overkill, I guess I need at least double the 3.58 Mhz pixel rate.

Slew rate and gain bandwidth are different measurements. Slew rate is the maximum rate of change of output, and limits the bandwidth at higher voltages only. Lower voltages at higher frequency have a lower rate of change. Do the calculation based on the frequency and voltage you're working with, leaving plenty of room.

I haven't looked at the specs of the CA3140 in detail, will compare them a bit later. From memory it's not really anything too special.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby natshaw on Tue Mar 19, 2013 6:36 pm

Carcenomy wrote:Actually I just realized something else - what's the SC-3000's schtick for getting audio out of it when you're not using RF?


The 5-pin DIN already has audio and video that should input to almost any TV's old school AV input (yellow video socket, and white/red audio sockets). Usual cable is DIN to RCA. Some TVs will be smart enough to realise that only left audio is connected, and treat it as mono, and put it out both speakers. Other TVs won't, and you might need a 2-into-1 RCA adaptor of some sort.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby natshaw on Tue Mar 19, 2013 6:45 pm

arjoll wrote:Slew rate and gain bandwidth are different measurements. Slew rate is the maximum rate of change of output, and limits the bandwidth at higher voltages only. Lower voltages at higher frequency have a lower rate of change. Do the calculation based on the frequency and voltage you're working with, leaving plenty of room.


Cheers. I thought (OK, I decided, without knowing!) that the slew rate was a factor in the gain bandwidth issue I was seeing, good to know the terms anyway. Regardless, my circuit sim shows the gain dropping at the frequency and voltages I need. Using NI Multisim v10 (sorry if I said SPICE earlier, habit). Simple enough circuit, so I will happily construct it and check the gain on my scope.

Edit: just to confirm, at lower frequencies, gain is fine.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby arjoll on Tue Mar 19, 2013 9:21 pm

natshaw wrote:Cheers. I thought (OK, I decided, without knowing!) that the slew rate was a factor in the gain bandwidth issue I was seeing, good to know the terms anyway.

You'll find that both figures have an effect. The bandwidth quoted at unity gain is a point on a graph - the bandwidth will go down as gain increases. Slew rate has an effect as well - in the case of the CA3140 the output can only move at 9V per microsecond, so that limits the frequency that it can output at any given voltage - in this case it's probably pushing it to do +/- 4.5V at 1MHz, but half that voltage you can probably do twice the frequency, subject to your gain bandwidth.

Being video there's lots of pulses/transients, so you may need to keep the transient response in mind. A short pulse in may have some ringing on the output - looking at the figures it could take up to 0.08uS to get to voltage and overshoot by up to 10% - meaning the leading edge of a square wave would be distorted. TBH I'd be inclined to suck it and see!

In terms of the CA3140 as an op-amp, the fact that the datasheet says it "replaces the 741 in most applications" sounds alarm bells - the 741 was great for it's time, but is certainly not a chip I'd use in anything these days!

Looking into more detail, and comparing it to my favourite op-amp (the TL07x series), the RCA device has higher unity gain bandwidth and better transient response, while the TL07x has far lower noise (which figures, I primarily muck around with audio circuits) and higher slew rate. The CA3140 is closer to being suitable for video, but I think it's probably pushing it just a little to get 4.5 MHz through it.

Have you looked at the datasheet? Figure 6 shows the gain/bandwidth curve, and figure 33 shows the effect of slew rate.

One final thing - all of the stats are running at +/-15V. If you're trying to run this on a single rail with virtual earth and decoupling (which we discussed earlier) then all bets are off. You may need to investigate a DC-DC converter onboard if you're going to power it from 9ishV.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby arjoll on Tue Mar 19, 2013 9:31 pm

Here we go - I think something like the AD828 is what you want. http://www.analog.com/static/imported-files/data_sheets/AD828.pdf

Compatible with single rails from 5V. Bandwidth at 2x gain and 5V rail of 10MHz min, 18MHz typical. Slew rate 200-250V/uS at 5V rail. 45nS to settle within 0.1%. $9.40+GST from element14. There's even a circuit there for a high performance video distribution amp running 0.1dB to 40MHz. Sweet.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby honestbob on Tue Mar 19, 2013 10:14 pm

arjoll wrote:Here we go - I think something like the AD828 is what you want. http://www.analog.com/static/imported-files/data_sheets/AD828.pdf

Compatible with single rails from 5V. Bandwidth at 2x gain and 5V rail of 10MHz min, 18MHz typical. Slew rate 200-250V/uS at 5V rail. 45nS to settle within 0.1%. $9.40+GST from element14. There's even a circuit there for a high performance video distribution amp running 0.1dB to 40MHz. Sweet.


:) Heh - great minds thinking alike, or something like that. I ordered a few of those AD828s off eBay earlier tonight. They are only $2USD each for the SOIC versions and $USD each for the DIP versions off eBay plus $3.50USD postage. I also ordered a few other things to play around with.

THS7314 - 3 Channel SDTV Video Amp with 5th order butterworth filters and 6-dB gain
http://www.ti.com/lit/ds/symlink/ths7314.pdf

Another alternative to that which looks quite similar is the NCS2553. It has the same pinout etc. Didn't get any of those though.

AD830 High Speed Video Difference Amplifier - similar family to AD828, but designed to do clean differential amplification (supposedly cleaner than using an Op Amp difference circuit directly). Might be handy for dialing back the Pb signal and subtracting a bit of -Y as 5-11under suggested.
http://www.analog.com/static/imported-f ... /AD830.pdf

NE592 differential video amplifier - same sort of idea. Looks like an older style of differential amplifier as some of the chips had an 88 date stamp, if I read the picture correctly. They were cheap though, so grabbed a couple anyway.
http://www.onsemi.com/pub/Collateral/NE592-D.PDF

A couple of SOIC to DIP sockets.

A couple of SOIC to DIP adapters where you can solder the SOIC chips to a mini PCB. Those might give me a bit of soldering practice :) I haven't done any surface mount soldering before.

The various bits and pieces above should start turning up in about 2-3 weeks time.

By the way - I only just figured out how to find most of the op-amp ICs on JayCar's website. Search for "op-amp". Sounds simple, but it took me about a dozen attempts. That little minus sign made all the difference for narrowing the search to a useful range.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby honestbob on Tue Mar 19, 2013 10:29 pm

natshaw wrote:
arjoll wrote:Slew rate and gain bandwidth are different measurements. Slew rate is the maximum rate of change of output, and limits the bandwidth at higher voltages only. Lower voltages at higher frequency have a lower rate of change. Do the calculation based on the frequency and voltage you're working with, leaving plenty of room.


Cheers. I thought (OK, I decided, without knowing!) that the slew rate was a factor in the gain bandwidth issue I was seeing, good to know the terms anyway. Regardless, my circuit sim shows the gain dropping at the frequency and voltages I need. Using NI Multisim v10 (sorry if I said SPICE earlier, habit). Simple enough circuit, so I will happily construct it and check the gain on my scope.

Edit: just to confirm, at lower frequencies, gain is fine.



Here's some light bedtime reading (in no particular order) for anyone interested in the 30 odd different parameters that describe op-amp performance and how to choose an op-amp for a given application. I'm afraid my eyes glazed over a bit when reading these and I settled for a Google and eBay search for things like "high speed op-amp" and "video op-amp" and seeing what other people have used for similar applications in the past :)

I'll try to understand the parameters a bit better when I have more time. At least I think I have the basic concept of how op-amps work now and the basic amplification and differential circuits.

http://www.electronicproducts.com/Analo ... _amps.aspx
http://www.embedded.com/design/embedded ... lar-op-amp
http://www.electronicproducts.com/Analo ... p_amp.aspx
http://qooljaq.com/OpAmps.htm

Cheers
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby natshaw on Tue Mar 19, 2013 10:34 pm

Great, thanks Arjoll, yeah the 3140 won't cope, agreed. AD828 looks the business!

Regarding physical connection, I've soldered some header pins onto some Veroboard, mates very nicely with the internal video connector - i.e. my PCB is a replacement for the one that's in there. Cable sits up vertical though, but no biggie. Had to use a small hand twist drill bit to make Veroboard holes a smidgen bigger.

Also, after a bit of thinking, I reckon the neatest solution I can think of for cabling is a panel-mount 7-pin mini din socket. It'd fit, right? Could squeeze it onto rear of case maybe? Could look really nice and neat, almost factory. Pair for Y, pair for Pb, pair for Pr, leaves one wire for audio, and using shared ground. Would mean a proprietary cable, from 7-pin mini male, to 4 x RCA.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby natshaw on Tue Mar 19, 2013 11:18 pm

Good op amp stuff, guys. Check this one out too, it's a cheapy triple, designed for YPbPr. http://media.digikey.com/pdf/Data%20Sheets/NJR%20PDFs/NJM2580.pdf
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby natshaw on Wed Mar 20, 2013 9:26 am

Also, these guys doing similar things, http://www.racketboy.com/forum/viewtopic.php?f=25&t=37716&start=70 but they seem to think that some TVs won't accept 240p (288p for PAL) and treat it as 480i/576i. I know it works on my Sony, easy test is just connect the Sega's standard composite output, to the TV's composite input, or to the Component input's Y (green colour) socket. If you get any sort of picture then you're watching 288p!
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby honestbob on Wed Mar 20, 2013 9:44 am

Here you go - a nice SC-3000 Test Pattern based on 5-11under's test pattern.

This is a RAR containing a WAV. You can connect a mono audio cable to your SC-3000 to load it via the cassette-in port (or load it into MESS)

http://sc3000-multicart.com/downloads/S ... rn1_01.rar

Here is the basic source for it for future reference.

http://sc3000-multicart.com/downloads/S ... attern.txt

It has the same test pattern that 5-11under distributes on a cart for his Colecovision component video mod. But it also has 15 screens with text in multiple colours where the background colour keeps changing. Just press any key to move from one test screen to the next. I haven't had time to try it on a real SC-3000 yet as I just wrote it in MESS this morning before the kids got up, but it should work fine.

Image Image
Image Image
Last edited by honestbob on Wed Mar 20, 2013 10:00 am, edited 1 time in total.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby honestbob on Wed Mar 20, 2013 9:54 am

natshaw wrote:I've soldered some header pins onto some Veroboard, mates very nicely with the internal video connector - i.e. my PCB is a replacement for the one that's in there.

Great idea. We should be able to to figure out a secure way of mounting header pins at 90 degrees to a PCB if we can't find a matching connector and if height is an issue when case is shut. Maybe just lots of glue and solder :)

natshaw wrote:Also, after a bit of thinking, I reckon the neatest solution I can think of for cabling is a panel-mount 7-pin mini din socket. It'd fit, right? Could squeeze it onto rear of case maybe? Could look really nice and neat, almost factory. Pair for Y, pair for Pb, pair for Pr, leaves one wire for audio, and using shared ground. Would mean a proprietary cable, from 7-pin mini male, to 4 x RCA.


Yes, that sounds like a good idea. My only comment on that is I find making up cables a real pain. It is surprisingly difficult to get everything connected to the correct pin without shorting out or having a couple of wires longer than the rest and then swearing and cursing as you try to bend and solder everything into place :) But yes, that sounds promising.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby natshaw on Wed Mar 20, 2013 11:09 am

Yep, if space an issue, can just use 90-degree header pins. I've only got them in 5x2 rectangular blocks, am sure can snip those or buy them in single rows, or buy connector from digikey, RS or whomever.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby natshaw on Wed Mar 20, 2013 9:52 pm

We have colour! Now, this is the non-amplified approach, and will not usually work. The amplitude of the Y signal is so weak, seems only to be detected some of the time. Amplification definitely needed on Y.

Colours actually look OK, the image is not as blue-shifted as it appears in these screenshots. It is dark though.

(Edit, whoops those are the red/blue swapped ones), try these instead:

Image
Image

Total cost: $1. Parts list: 3 resistors, some chopped RCA leads.
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Re: TMS9929 (Sega etc.) display direct to modern TV!

Postby Carcenomy on Wed Mar 20, 2013 11:10 pm

Man I shoulda paid attention earlier you totally pointed out that audio line on the DIN, my mistake :)

Looking good! It's really solid progress, how's it look for scaling when you tell that Bravia to stop the tomfoolery and go to 4:3?
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