Supergun AV with Sony CXA1645

[Greatsaintlouis]

Having recently aquired a fairly cheap King Of Fighters '96 MVS cart, I've decided to finally follow my dream to build a supergun in lieu of my eventual purchase of a MV-1 or MV-1F board (anyone selling one cheap?). For now, I'd like to have the supergun output composite AV to work on my TV (although I plan on making the connection from the harness modular so I could easily add in RGB support once I get the money/space for a dedicated monitor.) Now, I have no intention of spending ~$70 on a JROK encoder, and thankfully Antipasta came to the rescue with the suggestion that the Sony CXA1645 chip from a Playstation, Saturn (even Genesis?) could be shanghaied for that purpose. Has anyone here done this, or could provide a link to any sort of walkthrough/schematic for the circuit I'd need to make?

Also, I've got a fairly non-working NES that I plan on using for the shell of the supergun, which brings the question: it would be ghetto and lo-fi as all hell, but is there any way I could tap into the NES' AV outputs for this project and just use the encoder there?

[Calpis]

The CXA1645's datasheet has a recommended circuit. You can find the datasheet here: http://f5ad.free.fr/Docs_Composants/CXA1645.pdf

The NES doesn't use RGB so it doesn't have an encoder.

Only Genesis 3 have a 1645 IIRC, older Genesis/Master System/Neo Geo/Amiga have CXA1145. Also many Playstations have integrated video encoders.

[retro]

1145 indeed in a MegaDrive. You can do it with them, yup... although (especially the earlier ones) aren't superb chips. The best ones are rare as the excrement of a rocking horse!!! Still, if you have a sacrificial Genesis or Playstation, go for it!!

If you're going to be buying a chip, though... then use a JRok instead.

[Greatsaintlouis]

That's the whole reason I'm looking for a CXA1645 - I don't really feel like spending $75 on what I could do on my own for 1/3 of that. I've got an old, non-working SCPH-1000 model stashed away somewhere, so I've already got the chip as well - just need to get the assorted other bits from Radioshack.

Unfortunately, I think I'm going to need an interpreter as well - those datasheets appear to have just what I need, but I can't read electronic schematics to save my life. I've done a good bit of soldering projects, but they've all been things with "...For Dummies"-esque tutorials found online.

[retro]

Just use the application circuit on page 10.

Pin 1 goes to ground
Pins 2, 3 and 4 go to RGB In through 3 capacitors (parts list: 3 0.1uF capacitors, non polarized e.g. ceramic)
Pins 5, 8, 11 & 17 are not connected
Pin 6 is a subcarrier input - a sine wave or low voltage pulse (there are extra schematic examples in the notes, point 5)
Pin 7 goes to +5V if you're going for NTSC - it is the NTSC/PAL selector
Pin 9 is the Y signal clamp - just connect to ground via another 0.1uF cap (add to parts list)
Pin 10 is the sync input
Pin 12 is Vcc1 - the positive supply. It connects to the +5V supply. There are also two capacitors connected to ground in parallel on this line. They are a 0.01uF unpolarized, and a 47uF polarized (e.g. electrolytic). The polarized one has to go the right way round (+ to +5V)(add caps to parts list)
Pin 13 determines the internal reference current. Connect it to ground via a 47k resistor and 0.1uF polarized capacitor in parallel
Pin 14 in the internal reference voltage. Connect to ground via a 10uF polarized capacitor. The notes seem to suggest tantalum bead here.
Pin 15 *ERROR ON DIAGRAM* This is C out not Y out!!!! If you're not using S-Video, don't bother connecting anything here
Pin 16 Y out! As per 15, don't connect anything to this pin if you're not using S-Video
Pin 17 Internal filter FO adjuster. Connect to ground via a 20k 1% tolerance resistor for NTSC
Pin 19 Vcc2 - another voltage supply. Connect to +5V, and connect to ground via the same type of capacitors as for pin 12
Pin 20 Composite out. Connect via a 75 ohm resistor and a 220uF polarized capacitor
Pins 21-23 RGB out. Don't connect if you don't want RGB out
Pin 24 Connect to ground


By the way, is it a SOP in the Playstation? If so, be careful! They can be quite hard to solder/desolder sometimes!

For someone not into reading circuit diagrams, I would certainly recommend doing some reading up. The Babani range of books are great. Robert Penfold books in particular were great, I thought... and he's a nice guy! He helped me with a school project. http://www.babanibooks.com/bb7.htm I don't know if they are available in the US. Still, a browse through Amazon might be of use... look for books on schematics or circuit diagrams.

How about:

http://www.amazon.co.uk/exec/obidos/ASIN/0830628800/qid=1126020520/sr=8-2/ref=sr_8_xs_ap_i2_xgl/202-3423629-8203831

http://www.amazon.co.uk/exec/obidos/ASIN/0830676325/qid=1126020564/sr=8-1/ref=sr_8_xs_ap_i1_xgl/202-3423629-8203831

http://www.amazon.co.uk/exec/obidos/ASIN/0830686320/qid=1126020564/sr=8-4/ref=sr_8_xs_ap_i4_xgl/202-3423629-8203831

The middle one appears to be American, and should be on Amazon US.

[hl718]

Yeah, all the stuff on the original PlayStation is surface mount. Bitch to remove without damaging if you don't have a proper toolbench setup. A standard iron and desoldering braid just doesn't cut it. Nevermind the pins are small as hell as it is. Personally I'd find paying the $70 to be cheaper and more time efficient. :)

-hl718

[Greatsaintlouis]

Just use the application circuit on page 10.

Not to be a smartass, but if it was that easy I don't think I would have made mention of the fact that I don't understand a thing those datasheets are saying.

I appreciate your detailed pinout, but that still has me at a loss - I'm really not good with all that electronic lingo. I suppose that would be a pretty thorough walkthrough for someone with experience, but I've got no idea what all that means. Where do I get +5v from? Where and how do I connect the capacitors? Where's the RGB in from the Jamma harness? How does this hook up to a composite video RCA jack? Etc.

I may have a look through the school library and see if they have any basic electronic primers on my day off, or even (though I'm not holding my breath) those books you mentioned.

Either way, a $75 Jrok encoder might be easier, but I'm not sure I'd consider the price to be at all 'cheap', and I'd rather try to do it myself than pay someone $75 plus shipping for something I could conceivably pull off on my own. Plus, there's bragging rights involved that way. :-D

[retro]

Apologies, I didn't note that Pins 2, 3 and 4 are RGB IN - this has been amended.

Composite hooks up to Pin 20 - through the components mentioned above. Well, I tell a lie... a composite (phono) terminal is of course TWO pins... the outside barrel is ground.

You get +5V from your power supply.... I assume as you're making this circuit you're building a test rig, and you have a suitable PSU.

You'd want to make this on a PCB or stripboard. The components go where I mentioned above.. e.g. if a pin connects to ground through a capacitor, then its solder 1 end of the cap to the pin, and the other to the ground terminal.

Not trying to sound derogatory, but this is a simple circuit diagram. As such, it is a great way to learn to read them! You'll be able to pick up the circuit symbols from anywhere, e.g. here (http://www.kpsec.freeuk.com/symbol.htm). Note that they miss out a resistor symbol - the one that's kinda ---/\/\/\--- is also a resistor.

I'll try and do you a little electronics 101 diagram with the schematics in a sec.

[retro]

Hopefully this (amended) diagram clears things up.

I made some divisions to make things clearer. The red and orange sections are optional. The green and blue go to PSU and JAMMA connector respectively.

This leaves a few simple components - hopefully this makes it easier. For example, take pin 2. The pin connects to 1 end of a capacitor, and the other end of the capacitor connects to the R pin of the JAMMA connector.

The black dots you see in some places are connectors. This shows a fork in the circuit - where 2 things connect to 1 thing. I'll make some more diagrams to better explain this tomorrow - and a stripboard layout.

http://img283.imageshack.us/img283/4031/schem2wj.jpg

Parts List(for composite only)

Capacitors
0.01uF Ceramic x2
0.1uF Ceramic x4
0.1uF Tantalum Bead
47uF Tantalum Bead x2
10uF Electrolytic
220uF Electrolytic x2

Resistors
75 Ohm x2
47k
20k Metal Film 1% tolerance

Miscellaneous
Breadboard (size to follow)

That lot should set you back... what, maybe $5-10? Less if you're lucky!!! To locate the chip now, you might be looking at $40! crazy! Hurrah for old Playstations!!

I'll work on that SCIN when I'm more awake!!!

[Greatsaintlouis]

Wow, that's a lot more detailed than I really expected - thanks a lot! That last diagram you drew up actually makes things pretty clear - I'd almost hazard to say that I could possibly construct a circuit with that knowledge.


Not trying to sound derogatory, but this is a simple circuit diagram.
Oh, I know - I'm really that bad at reading circuits. I should probably take the time to learn though, especially when constructing my own supergun, no?

[retro]

Well, to be honest, you don't really need circuit diagrams for a 'gun. Its pretty straightforward pinouts. For the RGB to NTSC circuit though, yes.

Like I said, didn't mean that to be critical of your abilities.... more that BECAUSE it is a simple circuit, it should be a good one to study and learn from.

Didn't get a chance to do the stripboard layout at work... will do that later.

[hl718]

Retro> Where is he supposed to pull the SC input from?

-hl718

[retro]

I'm working on that, as I said! I'm thinking from a circuit using a hex inverter, such as a 7404. Pretty sure I saw another design using one of these... I'll dig it out. Needs a crystal and a few other components, of course!

*Edit*

One circuit! (http://www.nexusuk.org/projects/rgb2svid/circuit)

You could just pinch the SC generator from there, or use the whole circuit if you wanted. He has a nice stripboard layout all prepared... git!! hehe

[Greatsaintlouis]

<total ignorance> And what's the SCIN for, anyways? </total ignorance>

[retro]

Colour subcarrier... you want colour, don't you? ;)

Here's my modified version of his diagram, to look like the above. It is NTSC, with an NTSC crystal. If anyone sees any mistakes... blame the original author! Just kidding - let me know ;)

http://img120.imageshack.us/img120/769/scin9xb.jpg

*EDIT* Gah, mistake number 1! The chip is a 74HCT04

Parts list

Capacitors
10pF Ceramic
33pf Ceramic x2
10nF Ceramic
100nF Ceramic

Resistors
4.7M

Oscillators
3.579545Mhz Crystal

[Greatsaintlouis]

Okay, so let me see if I'm following this correctly: Pin 4 on this circuit above goes to Pin 6 on the CXA1645 circuit, but that's all, right?

And what's this mysterious 14-pin chip here, anyways? Also, is this 3.579 timing crystal something that would easily be obtainable at a typical Radio Shack, or would I need to rip it out of some other NTSC device (like, say, a NES...)

Really appreciate the effort you're going to on my behalf, btw.

[retro]

ARSE!!! I KNEW I'd left something out!!! It is a 7404 Hex Inverter, e.g. 74HCT04.

Crystals are common - that should be an NTSC crystal. Yeah you'll find one in a NES, maybe PSX, most consoles really... and yes Radio Shack should have them for like a dollar or two.

Yup, pin 4 to pin 6.

As I say, you could build his circuit... just leave out the composite stripper, as you should have sync anyway. I'll see if I can do a stripboard for the basic one tomorrow, though.

Oh, and I'd get two IC sockets if I were you, too! Better than soldering chips directly... just in case you make a mistake!

[Stone]

I made one of these last week with an AD724 from Analog Devices...free samples ;)

They're pretty simple in terms of application circuit - I did have a dead MegaDrive2 I ripped the encoder out of but I didn't want to mess about too much with the luma/chroma delay lines so I just redid it. I've reproduced my (rather sparse...sorry!) design document below:

Pin 1 - Video standard - Tie high with 10k resistor (NTSC), low (PAL)
Pin 2 - Analog GND - Tie low
Pin 3 - Crystal input - Crystal bypassed by varcap to ground
- One end of the crystal is put into pin3, connected to one end of a variable capacitor (I used a 0-22pF type). The other end of the varcap and the other end of the crystal both go to your ground.

Pin 4 - Analog 5V - Tie high
Pin 5 - On/off - Tie high with 10k resistor
- you can add a switch here to save power if you want - pull pin 5 low to disable the chip.

Pin 6 - Red in - Input, 75R to ground, 0.1uF cap coupled
Pin 7 - Green in - Input, 75R to ground, 0.1uF cap coupled
Pin 8 - Blue in - Input, 75R to ground, 0.1uF cap coupled
- These three are identical: red/green/blue inputs come in from your JAMMA connector to one end of a 0.1uF unpolarised capacitor, then the other end of the cap goes to the relevant pin. You can add the 75 Ohm resistors (between the input and ground) if you want; they're not strictly necessary but I used them.

Pin 9 - Chroma out - 220uF cap coupled, then 75R to output
Pin 10 - Composite - 220uF cap coupled, then 75R to output
Pin 11 - Luma out - 220uF cap coupled, then 75R to output
- Exactly the same as in retro's excellent diagram. Don't forget to attach the ground lead on the socket to circuit ground!

Pin 12 - Mode select - tie low (FSC operation)
- This chip can run in a couple of modes. With pin12 pulled low you need a 3.579545MHz crystal for NTSC and 4.433619MHz for PAL. Use a parallel-resonant type with a shunt capacitance of around 18pF. Also don't forget that if you make it PAL then your TV/monitor must support PAL60 or it won't work with the majority of arcade boards!

Pin 13 - Digital GND - Tie low
Pin 14 - Digital 5V - Tie high

Pin 15 - VSYNC - Tie high with 10k resistor
Pin 16 - HSYNC - Composite sync
- Just run a wire straight from composite sync on the JAMMA connector to pin16. If you have separate HSYNC and VSYNC available then use both pins, if you only have composite sync then you need to tie pin 15 high and input it to pin16.

Putting a nice big capacitor (I used a spare 220uF one) across the 5V/0V connections is also sensible.

Put that lot together and it should all work! Hopefully that'll help somebody...total parts cost was probably about £5 so it's a pretty cheap option :)

Stone

[Greatsaintlouis]

Just noticed your addition to this thread - thanks a lot for the added info!

The project's been on hiatus for a while, as finding a cheap MV-1 or MV-1F board to go WITH my Supergun has proven rather difficult. Plus, I haven't had a chance to get back to my parents' place and see if I still have that old PSX I can pull the CXA from. And with school starting, and still working a part time job - well, free time has been at a premium, let me tell you.

I wonder if my bosses would mind me soldering things at the front desk of a hotel...

[Blur2040]

I ordered one (yay for free samples indeed) but I've realized that the chip is incredibly small...like 10 millimeters long. Can you mount that on anything? Or did you even bother? I'd like to do this as neatly as possible (for me, anyway).

Edit: Sorry, I'm electronically inexperienced...and well...would like to understand your directions better.

Edit Again: Ok, I think I understand things a little bit better, but don't you need some kind of variable resister (called a potentiometer, right?) to tweak the R, G, and B signals? Or are those what the 75ohm Resisters are for on the RGB inputs and the Chroma, Composite and Luma outputs for? Or am I just missing something?

[Gavindo]

This is a custom designed video conversion circuit (much as in any console), so you shouldn't need pots.

Which chip did you go for? What kind of pinout is it? If it is standard DIL, you should be able to mount it on stripboard.

[Blur2040]

I went for the AD724 from Analog Devices, the one Stone used. They're waiting for me at my house now...and I'm away at school...but I'll get at them soon enough.

I did eventually realize that I was just looking at some stripboard with huge holes, so I don't think I'll have any trouble mounting it. I'll just have to buy some extra components and brush up on my soldering skills first :o)

I really won't need any way to adjust the RGB coming in? I thought that certain boards might output weaker or stronger RGB signals than others, and that was the point of em. I thought it would be different than a console as I would be chaging hardware with each board...but then again, I'm a little bit on the dense side about this sort of thing.

[AntiPasta]

As your attorney I advise you to spend less than $1 for 3 (linear) 10K potentiometers. This allows you to adjust the RGB signal level.

[Stone]

I went for the AD724 from Analog Devices, the one Stone used. They're waiting for me at my house now...and I'm away at school...but I'll get at them soon enough.
Be warned, they're a right bastard to solder to. Really what you want is one of these:
http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=80010&STK_PROD_CODE=34-0910

Basically they're a standard PCB with the pins from the SOIC brought out to bigger pads - you just solder the chip to the board, then you can add wires of whatever to the pads. I used a combination of that and stripboard(with wires linking the two) to construct my adaptor. Part number #34-0910 is what I used, you should be able to find something similar from a supplier closer to you :)

Stone

[Blur2040]

Thanks for the advice, Stone, AntiPasta. Hopefully I'll be able to walk into my local Radio Shack and get most of what I need. I plan on pretty much going in, asking if they have anything that I can mount it on, and go from there.

[Stone]

Good luck! It's a lovely little project when you get it working, very satisfying :D

Stone

[Blur2040]

Ok folks, I haven't gotten to the point where I can start making this thing (I have to wait to the weekend after this one to go to my house and get a power supply and the AD724s), but I'm starting to get ready. That means finding the parts I can't get locally online.

First thing I need is something to allow me to mount the AD724 onto pegboard...I didn't know where to find that little board Stone suggested...but I found... THIS A726-ND (http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=326640&Row=238137&Site=US)
(Beware 56k, it's a PDF! Click on that technical data link...and it gives you options to learn about the dimensions and specs of it)

It's an SOIC to DIP adapter. A DIP has standard .1" spacing between pins and would fit on pegboard...right? And...more importantly...will that adapter fit the AD724? I've tried reading the measured diagram for the AD724 HERE (http://www.analog.com/UploadedFiles/Data_Sheets/40671345AD724_b.pdf) (56k warning again...and the diagram is at the last page, btw) but it doesn't match up the way I'm measuring it. So...is that what I want?

Edit: Ok, I looked at the measured diagram again...and the SOICs have .05" pin spacing, and the "G" dimension on the A726-ND is .350" long...the AD724 has 8 pins...and 7 spaces...and .05" x 7 is .35". So, I think I've found what I'm looking for...but a confirmation would be nice.

Next question involves resistors. You guys gave me the Ohm rating on the resistors (I believe the only ones in Stone's setup are 10k ohm and 75 ohm), but I need a wattage as well...and I'm lost. In addition...there's a whole bunch of different types (materials) resistors...I assume anything would be fine as long as it meets the ohm/wattage requirements.

I guesss I have a question about the capacitors. They all have different voltage ratings...so...for this I assume I just have to get ones that are at least 5 volts...as this thing runs on 5 volts. Oooh...and once again...theres a whole bunch of different types...so I'm curious as to what to get...

The NTSC crystal/oscillator (3.579545 mhz, right?)...the ones i'm looking at (they've all been on www.digikey.com as I like their search system) have a pF rating...and once again I'd like to know if that even matters.

Gah...I might as well ask my last question...the variable capacitor that's near the crystal...on the Analog devices website it suggests a 10-30pf varcap...and Stone, you said you used a 0-22pf...(I can't find anything online that matches either of those right now btw...). What is that thing for btw...I didn't see any explanation that I understood in the documenation for the AD724...so...I'm curious about that too.

Ok, I'm pretty sure thats all the questions I have. I have a drawn up a plan for how I'm going to do this (quite a nice one in fact) but I just wanna make sure I've got everything right.

[the_steadster]

Ok folks, I haven't gotten to the point where I can start making this thing (I have to wait to the weekend after this one to go to my house and get a power supply and the AD724s), but I'm starting to get ready. That means finding the parts I can't get locally online.

First thing I need is something to allow me to mount the AD724 onto pegboard...I didn't know where to find that little board Stone suggested...but I found... THIS A726-ND (http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=326640&Row=238137&Site=US)
(Beware 56k, it's a PDF! Click on that technical data link...and it gives you options to learn about the dimensions and specs of it)

It's an SOIC to DIP adapter. A DIP has standard .1" spacing between pins and would fit on pegboard...right? And...more importantly...will that adapter fit the AD724? I've tried reading the measured diagram for the AD724 HERE (http://www.analog.com/UploadedFiles/Data_Sheets/40671345AD724_b.pdf) (56k warning again...and the diagram is at the last page, btw) but it doesn't match up the way I'm measuring it. So...is that what I want?

Edit: Ok, I looked at the measured diagram again...and the SOICs have .05" pin spacing, and the "G" dimension on the A726-ND is .350" long...the AD724 has 8 pins...and 7 spaces...and .05" x 7 is .35". So, I think I've found what I'm looking for...but a confirmation would be nice.

Next question involves resistors. You guys gave me the Ohm rating on the resistors (I believe the only ones in Stone's setup are 10k ohm and 75 ohm), but I need a wattage as well...and I'm lost. In addition...there's a whole bunch of different types (materials) resistors...I assume anything would be fine as long as it meets the ohm/wattage requirements.

I guesss I have a question about the capacitors. They all have different voltage ratings...so...for this I assume I just have to get ones that are at least 5 volts...as this thing runs on 5 volts. Oooh...and once again...theres a whole bunch of different types...so I'm curious as to what to get...

The NTSC crystal/oscillator (3.579545 mhz, right?)...the ones i'm looking at (they've all been on www.digikey.com as I like their search system) have a pF rating...and once again I'd like to know if that even matters.

Gah...I might as well ask my last question...the variable capacitor that's near the crystal...on the Analog devices website it suggests a 10-30pf varcap...and Stone, you said you used a 0-22pf...(I can't find anything online that matches either of those right now btw...). What is that thing for btw...I didn't see any explanation that I understood in the documenation for the AD724...so...I'm curious about that too.

Ok, I'm pretty sure thats all the questions I have. I have a drawn up a plan for how I'm going to do this (quite a nice one in fact) but I just wanna make sure I've got everything right.


All caps except for the last one (220uF) want to be non-electrolytic as they are for AC signal. A voltage rating of 5V or larger will be fine. Resistor max power you probably will be fine on 10W and material doesnt really matter
The capacitance of the oscillator, stone mentioned a 18pF shunt capacitance - I'm not certain what this means, but I'd guess it is what the specs are referring to.

Afraid I don't know much about the mountings or var cap, except that 0F means it is just directly connected - i.e. no charge stored. I've no idea if this is important or not

[Stone]

First thing I need is something to allow me to mount the AD724 onto pegboard...I didn't know where to find that little board Stone suggested...but I found... THIS A726-ND (http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=326640&Row=238137&Site=US)
(Beware 56k, it's a PDF! Click on that technical data link...and it gives you options to learn about the dimensions and specs of it)
That is EXACTLY what I was looking for when I built mine. :DOH:


It's an SOIC to DIP adapter. A DIP has standard .1" spacing between pins and would fit on pegboard...right? And...more importantly...will that adapter fit the AD724? I've tried reading the measured diagram for the AD724 HERE (http://www.analog.com/UploadedFiles/Data_Sheets/40671345AD724_b.pdf) (56k warning again...and the diagram is at the last page, btw) but it doesn't match up the way I'm measuring it. So...is that what I want?
Yes. Buy 3 and keep them, you never know when they'll come in handy ;)


Edit: Ok, I looked at the measured diagram again...and the SOICs have .05" pin spacing, and the "G" dimension on the A726-ND is .350" long...the AD724 has 8 pins...and 7 spaces...and .05" x 7 is .35". So, I think I've found what I'm looking for...but a confirmation would be nice.
You're right, the AD724 is a 16-pin SOIC, so what you posted is exactly right. Good find; if Digikey didn't gouge so heavily on shipping to the UK I'd get a couple.



Next question involves resistors. You guys gave me the Ohm rating on the resistors (I believe the only ones in Stone's setup are 10k ohm and 75 ohm), but I need a wattage as well...and I'm lost. In addition...there's a whole bunch of different types (materials) resistors...I assume anything would be fine as long as it meets the ohm/wattage requirements.
I used 1/4W metal-film ones because that was what I had spare - you can get eighth-of-a-Watt ones too, but the only real advantage is that they're slightly smaller. Use whatever you can get your hands on readily; 1/4W will be just fine. The type doesn't really matter as long as the resistance is the same.


I guesss I have a question about the capacitors. They all have different voltage ratings...so...for this I assume I just have to get ones that are at least 5 volts...as this thing runs on 5 volts. Oooh...and once again...theres a whole bunch of different types...so I'm curious as to what to get...
For the 0.1uF caps on mine I used ceramic disk types that look like this:
http://www.guitarpartsusa.com/ccp51/media/images/product_detail/CAP-022.jpg

Voltage rating doesn't really matter for those ones, I used some I had lying around. For the 220uF caps on the output I used 16V electrolytic types (look like this: http://img.alibaba.com/photo/50312359/Aluminum_Electrolytic_Capacitor.jpg ) but again it doesn't really matter. Make sure the positive leg is attached to the chip leg as per retro's diagram, the negative leg is usually the one that's marked on the capacitor body but I'm sure you can figure it out.


The NTSC crystal/oscillator (3.579545 mhz, right?)...the ones i'm looking at (they've all been on www.digikey.com (http://www.digikey.com/) as I like their search system) have a pF rating...and once again I'd like to know if that even matters.

Gah...I might as well ask my last question...the variable capacitor that's near the crystal...on the Analog devices website it suggests a 10-30pf varcap...and Stone, you said you used a 0-22pf...(I can't find anything online that matches either of those right now btw...). What is that thing for btw...I didn't see any explanation that I understood in the documenation for the AD724...so...I'm curious about that too.
It is indeed 3.579545MHz you want. As long as you get a 'parallel-resonant' crystal the pF rating doesn't really matter - I'd get one of about 16-22pF if available, if not then lower is slightly more convenient. The reason you need the varcap is that the crystal is only specified to oscillate at such a closely defined frequency when it has a very precise capacitance across it - when you add capacitance by attaching it to a PCB, bits of wire and so on it could in theory oscillate far enough from its specified frequency that your TV wouldn't be able to pick it up - outcome of this is no colour (or a picture that flickers between being in colour or in black and white). By tuning the varcap you can ensure that the crystal always oscillates at the right frequency, so it starts up in full colour every time. Once this is set you'll never need to move it ever again but it's worth having just in case your crystal isn't quite in tolerance. When I first made mine my TV couldn't quite get the signal on powerup, until I touched one leg with a screwdriver (changing the capacitance) to make the crystal oscillate correctly (ie, I got a colour picture). Changing the varcap setting and powering it on and off a few times to check it fixed this :)


Ok, I'm pretty sure thats all the questions I have. I have a drawn up a plan for how I'm going to do this (quite a nice one in fact) but I just wanna make sure I've got everything right.
Sounds like you're pretty much sorted out. Best of luck :)

Stone

[Blur2040]

Ok...I hate to be the guy full of questions...as this has probably been more than annoying already...but...we've already started our way down that slippery slope...

A few more questions!

The 220uF capacitors...they should be DC, right? Digikey has ones that are listed as DC...and ones that are not...which I assume are AC. I just want to make sure I have it right...

Oh, and Stone, you said...


Putting a nice big capacitor (I used a spare 220uF one) across the 5V/0V connections is also sensible.

Does that refer to the connections that go directly to ground or +5v...like pins 12, 13 and 14 for example. Ah...and those should be DC as well, right? I'm a sensible guy...so if you say it's sensible...I might as well do it. Oh...maybe a little explanation of the reasoning behind those would be nice...for future reference.

I thikn that's the last thing I need...I've got everything else picked out (though I did have a problem or two finding .1uF capacitors that didn't look like little bricks w/o leads on them [i found some i think will work]), but I just want to make sure i have everything right. As I might be a tad disappointed if this doesn't work.

Edit: Crap, one more thing...what sort of voltage would I need on that variable capacitor?

Edit Again: Ok, I found a 5.2-30pF 100v varcap that I can buy one at a time that's at a reasonable price...I'm gonna assume that'll be okay. The diagram on Analog devices site suggets 10-30pF...and you suggested 16-22pF...and well the one I picked doesn't exceed the maximum capacitance, and I don't see why going lower could hurt it...though please slap me if I'm horribly wrong.

[Stone]

Ok...I hate to be the guy full of questions...as this has probably been more than annoying already...but...we've already started our way down that slippery slope...

A few more questions!
D'oh :D


The 220uF capacitors...they should be DC, right? Digikey has ones that are listed as DC...and ones that are not...which I assume are AC. I just want to make sure I have it right...
DC is fine.


Does that refer to the connections that go directly to ground or +5v...like pins 12, 13 and 14 for example. Ah...and those should be DC as well, right? I'm a sensible guy...so if you say it's sensible...I might as well do it. Oh...maybe a little explanation of the reasoning behind those would be nice...for future reference.
No, put a reasonably sized capacitor (220uF is plenty) directly between the 5V and 0V wires going into the circuit. The basic principle is this: the chip draws way more current from the power supply when it's switching signals on and off than when it's just sitting there. Every time it switches a momentary 'glitch' appears on the power supply (so the 5V line might go to a bit lower or higher value, briefly) which can either damage the chip (rare) or make it misbehave (more common). If the supply voltage drops below the specified minimum for the chip it's no longer guaranteed to work, so it's usually a bad thing.

If you put a capacitor across the PSU lines, when the glitch would have happened a little bit of charge is drawn out of the capacitor to fill the deficit, so the supply stays stable. Once the glitch has passed the capacitor refills and all is well :) DC caps are what you want here as well.


I thikn that's the last thing I need...I've got everything else picked out (though I did have a problem or two finding .1uF capacitors that didn't look like little bricks w/o leads on them [i found some i think will work]), but I just want to make sure i have everything right. As I might be a tad disappointed if this doesn't work.

Edit: Crap, one more thing...what sort of voltage would I need on that variable capacitor?
So long as you hook everything up right it should be just fine :)

The varcap I used was #12-0105 from http://www.rapidelectronics.co.uk - if yours looks similar then it'll most likely work fine.


Edit Again: Ok, I found a 5.2-30pF 100v varcap that I can buy one at a time that's at a reasonable price...I'm gonna assume that'll be okay. The diagram on Analog devices site suggets 10-30pF...and you suggested 16-22pF...and well the one I picked doesn't exceed the maximum capacitance, and I don't see why going lower could hurt it...though please slap me if I'm horribly wrong.
Mine actually covers the range 2-22pF, in the original post I meant they should go from 0-16pF or 0-22pF. Sounds like you've got the right thing anyway :)

Stone

[Blur2040]

Wow, tanks a lot once again, Stone. I think i've got everyting sorted now.

It almost seems as if I actually believe what you're talking about. I was giong to put a fuse on the incoming power line on the board...which would blow out if there was too much power coming in...but your idea seems like it would work a little bit better.

I've ordered my parts now...so...I'm set. Yay!

[Stone]

You almost certainly won't need fuses. If you hook it up wrong you'll have other problems, like your TV going bang ;)

A fuse from the PSU to the game board is a sensible precaution, for something like this (cheap as anything) it's not really necessary. I didn't bother, anyway :)

Stone

[Greatsaintlouis]

And this thread rises from the grave once again. I finally got my hands on my old Playstation, and the chip, though tiny, definitely looks solderable.

However.

The chip in my PSX seems to be a CXA1645M. Is there any major difference between the 1645 and 1645M?

[Adeptus]

I'm looking to build a Supergun myself... I have a MK PCB that I'm dying to use...
Someone recommended the CXA1645, then I saw this post by ConsoleFun... (http://assemblergames.com/forums/showpost.php?p=102699&postcount=9)
A complete 1645-based RGB-to-composite circuit ready made, and cheap too.
It outputs to PAL, but that's what I want. (If you wanted NTSC, it would just require changing the crystal I think?)

[madhatter256]

The only difference between the 1645 and the 1645m is the physical size. I remember looking thru the datasheet for the 1145 there was the M model and P model and the only difference was the size, the pinout in each of them are the same.

Q about capacitors. The microF unit of measure is what counts, right? not the voltage? I found some 22uF capcacitors but they some of them have 16volts on them and 110v on others. How important are those?

[the_steadster]

Doesn't matter on the voltage, as it'll be moderately small voltages they'll be used with - mostly 5v and possibly 12V for the power supply to the board. a 16V cap would be fine.

[madhatter256]

So the voltage on the cap means the maximum amount it can take?

[duckzero]

I have been reading over this thread, and it seems to answer most of my questions. One thing I was looking at was just keeping the playstation physically intact, so I can just have the RGB and Sync go into the encoder and leave the playstation to power the chip. Now, would that be possible? I'm guessing that it would just take me lifting the pins from the R,G,B and sync and just attaching them to the same lines on the JAMMA harness (this is for a neo geo). Do I need to place a few resistors and things between the RGB lines and the encoder? And if so, what do I need?

My main concern is that the voltage at which the lines from the jamma harness will be too high and fry the chip.

[retro]

Err no, don't do that! Get a chip from a sacrificial machine, and power it from the PSU of the 'gun. Or, get hold of a suitable encoder from your favourite electronic parts supplier. There is absolutely no reason to leave it in the PSX - no reason to use the PSU from the PSX and the PSX itself would be useless then anyway.

See my diagrams for a description of ALL parts you need. I can't remember if I mentioned, but if you want to you can put pots on the RGB lines.

[electrochip]

great schematics and write up. will be using this soon.

[l_oliveira]

Just for information, the CXA1645 (and 1145 in the same way) are extremely picky with the voltage level on their sync input. The proper voltage at the sync pin is peaks somewhere around 2v.

Because arcade boards are extremely different from each other just keeping a certain margin of tolerance I've added a sync filter based on the LM1881 (which aways output the same TTL level) and a resistive voltage divider.

That would make the image stable in all possible setups and make the RGB encoder board more versatile as it would work with other things as well. :thumbsup: