Supergun AV with Sony CXA1645

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.

 

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 )

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.

 

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.

 

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

 

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.

 

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

Stone

 

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
(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 (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

 

That is EXACTLY what I was looking for when I built mine. OH:

Yes. Buy 3 and keep them, you never know when they'll come in handy

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.

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.

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.

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

Sounds like you're pretty much sorted out. Best of luck

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!

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...

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.

 

D'oh

DC is fine.

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.

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.

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

 

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!

 

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

 

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?

 

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...
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?)

 

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?

 

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.

 

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

 

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.

 

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.