I built a RGB to NTSC converter based on an AD724 from Analog devices using the pinout in the other thread....and what I got is something that kinda works. OK...I have to eat dinner right now...but the output picture I'm getting is in black and white...and it's kinda shaky...simliar to scrambled cable TV i guess...like the picture can't quite stay straight (but its real close). Can anyone give me something to check on? I don' think theres any shorts anywhere, and I've checked all my connections. I'm thinking/hoping it might be something dumb.... Lemme know if you need more info! Thanks! Edit: Oh yeah, i have no Arcade boards as of yet, so I"m getting my RGB signal from a Sega Genesis M1...is that a problem... Oh...For a brief second, I accidentally plugged my Ground into +5v...and the next time I turned the thing on, the picture was darker...and has stayed that way. It doesn't looked like anything is destroyed on the board...but did I fry anything? I mean...everything still works. Edit again: Forgot to mention that I'm hooking it up through composite video...I dunno, maybe i just suck at electronics and should buy a supergun if I want one.
I hate to be the guy who bumps topics...but I gotta bump this as I'd like some sort of suggestion. I think I was really close. I might just try it again and try to do it neater, but any tips would be nice. Tips as to what sort of wire I should be using to hook this up (from trace to trace on the board) would be nice too...as I was using really crappy copper wire (a single piece of copper) from the inside of a phone wire...but all else I had was 18 guage...and that wouldn't fit through the holes. I left my converter at home...but I'll be able to mess with it again in a few weeks...and I have the parts to try building another one.
If the picture is darker now you shorted 5V to 0V it sounds like you might have killed the AD724...they're not very tolerant of stuff like that :/ Hopefully with luck it'll be ok. Try twiddling the varcap - turn it all the way to one side, then move it a little the other way, power-cycle and try again. Some TVs (like mine) won't lock onto the colourburst properly if it's not correct from the get-go. Keep going until you've gone through the whole travel of the varcap...sounds to me like the colourburst's the only thing not working right. On mine if you short out the crystal (or remove it) you get a stable image in black and white, but if you change its capacitance (by touching one leg with a bare metal screwdriver, say) then the picture goes both black+white and 'wobbly' as you describe. I'd be looking for small shorts around the crystal area, if I was you. Stone
Damn. Well, the picture still came through after I accidentally shorted the five volts to ground...so I assume it was still working...as the signal was still coming through...but I probably did fuck it up. I didn't know I had to power up again each time i adjusted the capacitor. Bottom line though is that I'm going to try building this thing again when I get home again for holiday break. I built it rather hastily (but without shorts, I assure you!) over the Thanksgiving holiday...but things went surprisingly smoothly. I still have plenty of parts left (yay for buying extras) so I think I can do it again a bit slower and get it to work.
Ok, I posted the following at neogeo.com, but nobody really seems to be biting right now, so I thought I'd post it here for you guys...maybe in my description of what I did, you can find something wrong...I built this thing again...so...as you might imagine I'm a little bit annoyed...I might just end up breaking down and buying an encoder: Hey folks...I gues its hard for anybody to give me a ton of help without looking directly at my encoder...but... I"ve built an RGB to NTSC encoder for the purposes of using it with a supergun... But I don't have any arcade boards around to test it with...so...I've started by testing it out with the RGB output from various home consoles...IE my AES and my Genesis. ...and all I get is something that looks like scrambled porn... So...I suppose my first question for anyone is...Will home consoles put out an RGB signal just like an arcade board? I pretty much did (with the help of another design via the internet) what's on the AD724 data sheet at analog devices...but I'll tell you what I did anyway... Pin 1 goes to a 10kohm resistor then to +5v Pin 2 goes directly to ground Pin 3 goes into one end of my variable capacitor and also connected to my 3.57etc mhz NTSC clock. The ends of both the capacitor and the crystal are grounded. Pin 4 goes to +5v Pin 5 goes through a 10kohm resistor, then to +5v Pin 6,7,8 are the RGB inputs...tracing back from the AD724...theres a .10 uf ceramic capacitor....then theres a 10kohm resistor....and after that is where I have my terminal for R, G, or B. Pin 9 isn't used yet...it's some component of S-video...which I'm not using yet... Pin 10 is my composite video....the signal comes out of pin 10...then goes through a 75 ohm, 1/4 watt resistor...then through a 220uf electrolytic capacitor...(positive pin towards the chip) and then that's it....it goes to an RCA compoite jack....the center is the Signal, the outside is ground. Pin 11, svideo, unused pins 12 and 13 are grounded pin 14 goes directly to +5v Pin 15 goes through a 10k ohm resistor...and then goes to 5v Pin 16 is where I input composite Sync... I have everything connected to terminals for easy connection. The picture I get look something like scrambled porn... Lets say i connect it to my AES w/ Sam Sho 2. I turn on the Encoder (hooked to a PC power supply) first. Some lines go across the screen... I turn on the Neo, and I can see the neo geo logo coming up. The picture tries to stabalize...but can't quite cut it. The colors go a bit strange. Then things cut out. After a second, I see the "The future is now" thing flash on the screen for a second....then I see it go through all of the intro...except theres a huge black portion at the bottom of the screen...the intro is going on uptop...but it can't keep the screen still...and all the colors are still screwy... One thing I have to ask about is about my Variable capacitor...it doesn't seem to have any extremes...I can turn it as far as I want in either direction...it never stops.... I'm sorta stumped here...anybody have any idea what I'm doing wrong? I know I could buy a nice NeoBitz...or that crazearcade one...or that other one whose name I can't come up with off the top of my head...but I'd like to do it myself... Any help would be appreciated.
er, well, i think i described the way I did that wrong...but if I recall, you said the resistors aren't necessary... Let me describe that again... So, the R, G or B signal comes into the board, goes to 1 leg of a 10k ohm resistor, the other leg of that resitor goes to ground. Past the resistor...in the same line of traces, it goes into a .1uf ceramic capacitor, then it goes to the ad724... I tried it without the resistors before, and I got no picture, but I'll give it another try. Heres a pic
Take them out. They're in the right place but they should be 75R or not there at all Oh, and don't forget to put a big capacitor across the 5V/0V lines (negative lead to 0V, obviously). If you have any of the power pins attached to each other they should be joined near to the chip and then only a single pair of wires run to the PSU. Stone
Doh! I can't believe I did that...I'll replace the 10k with 75 ohm ones...and I'll add the capacitors and double check to make sure the power pins attached. Edit: Hmm...I guess I have one last question...with regards to putting the capacitors across the 5V and 0v lines...er...i guess I just don't know how that works. So...would it be like.... 5V in into positive leg of capacitor...and then all my 5V connections can go in after that... and the same thing with 0v? Or is this something different that I'm not understading...?
You're bridging the PSU with the capacitor. What I'd do (and did! ;-) ) is designate one track on the stripboard as 5V and one as 0V. Then hook all your chip's power connections directly to one of those tracks (with as short wires as you can manage), put a big cap between the two tracks and then have one wire to the PSU for 0V and one wire for 5V. The idea is that any PSU fluctuations will be smoothed away by the large capacitance. If it helps you to think about it, it's effectively increasing the resistance to change of the system - if you have a sharp voltage transition (say 5V to 2V) it'll take longer to get to 2V than it would have without the capacitor. I was trying to get away with not drawing a picture, but if you're still confused I'll see what I can sort out :icon_bigg Stone
Ok, I get what you're saying now. It probably won't fix my problems, but oh well. I've gotten it to the same point my other converter was at... I can see what's going on in the game most of the time, but theres no color going on (aside from when I first power it up) and its all squiggly. I may just give up and break down and buy a converter, because I have no clue how to fix this. But in the meantime, I'll add that capacitor.
My suspicion is a duff resonator and/or a bad PSU. If you have an oscilloscope you could check for transient noise in the PSU, if not just use a meter and check it's actually 5V and not too much less. If you remove the connection to the oscillator input of the chip altogether you should just get a greyscale image - if you get a stable video signal with it removed then that's definitely your problem. Crystals are a pain to design around; you can buy oscillator 'modules' which are a small metal can shape - you put 5V and 0V into them and get a nice square-wave out at their specified frequency. If you find your colour subcarrier circuit is bad then one of those might help you. Other than that I'm really not sure what to suggest...for me it 'just worked'. Stone
Thanks for your suggestsions again, Stone. I'm no electronics expert...so maybe I'm just doing something incredibly dumb that I might never figure out...that said though, I'll definately test out another power supply. The one I have wasn't from a particularly great computer, so who knows, that might be the problem. I'll borrow another one from a friend though, and maybe I'll have more luck. Even if I don't get this working, I'll still be farily pleased with myself. Honestly, even if the board I made doesn't quite work, it looks really nice...almost as if I know what I'm doing. On top of that, I've gotten experience which is always good. I think that if I actually buy a pre built encoder...like NeoBitz or something, I'd be able to easily put together a working supergun. So, for now I'll continue tweaking. I plan on finding a local distributor today that will sell me a Jamma board and harness, so I can stop testing on a Sega Genesis...and with an arcade board around, I'll be bound to get some sort of supergun working eventually. Bottom line: No matter what, I've enjoyed putting this thing together, and the experience I've gotten makes me pretty damn sure I'll get something together eventually. PS: I pity those who plan on working with the sony chip pulled from a Genesis or Playstation. I popped a Genesis open while looking for another oscillator (I eventually did find one in an Atari PC) and that chip was TINY, and has more pins than an AD724...AND you have to remove it...and that seems impossible.
Woah, woah, hang on...you're using a PC PSU with just the encoder powered from it? If you still have the standard drive connectors on it, try plugging in a coiuple of old CD drives or similar. PC PSUs (as with all switching PSUs) have a nasty habit of giving you totally wonky voltages if they're not sufficiently laden... For arcade parts my recommended retailer is Bob Roberts at http://www.homearcade.org/BBBB/ - he's helped me out many a time. Have a look Stone
Using an AT PSU? Yuck, yeah! Get a decent PSU for a start - arcade PSUs are cheap, and a lot more stable I find! Sounds like you have no sync. Err, did you look at the schematics I drew up for GSL? It is for a CXA1645, though... but they are common in consoles Also, did you put in a colour subcarrier circuit? Or does the 724 not need one?
Oh, well, for the record, I switched over to an Atari 8 bit PSU (don't worry, it's +5v), but it still doesn't work. Things look fine when I have the blue, red and sync plugged in, but as soon as I add in green, it goes all crazy and out of sync. I just don't get it. It's at home right now, so I can't mess with it, but I will eventually get some sort of working supergun together...probably.
I guess it could be the Genesis. I'd try a board if you can borrow one, the edge connector should set you back $5-7. Perhaps it should use the other value of NTSC crystal (14.318180MHz), but I doubt it. Jeff's a reliable person, if he said you built it right then you did! It desyncs when you connect green? Hmm, very strange! I'm not too sure those resistors should be there, regardless of value. Did you try without? I'd say it could be a combined composite/sync, but genesis has seperate sync and video pins. Hmm, a puzzler!
I did try it with the resistors out. I tried pretty much everything I thought wouldn't fry the AD724. I'll start work on it soon enough, and buy a board. I have none around as I sold them off with my cabinet (
