Amiga RGB to S-Video + composite adaptor
Here's a little adaptor I made to connect my old A500 and A1000 to my TV's s-video input. It's based on the same chip used in the Neobits adaptor (see this thread: http://eab.abime.net/showthread.php?t=29181) but with two fewer parts, and it plugs into the video port instead of being soldered to the motherboard.
This is the top. I cut a 25-pin connector down to 23-pin for the video port connection. http://www3.telus.net/narmi/top_small.jpg The circuit is virtually the same as the one in the AD724 datasheet, not too many connections as you can see from the bottom. http://www3.telus.net/narmi/bottom_small.jpg The video quality is very good, much better than the A520 I cannot find :). The hardest part was soldering to the chip, it's only available as a surface mount part, but it was worth it. We don't have TVs with RGB inputs on this side of the pond. Right now I'm working on a PCB layout for this so I can make another neater version. |
Cool!
Looks nasty-soldered but it's what I like in home-made stuff :D |
@Narmi
Welcome to the EAB, i am sure you will like it here :D I love hardware mods, especialy ones that take something and put it into something more usefull (LIKE S-Video!!) I wanted to do something like this for the A1200 and A600 that i have! So a BIG Thanks for the pictures!!! would you of made your own schematics ? |
If you want to get S-Video out of the A1200/A600, you don't need many components. The Sony video encoder chip near the PSU connector already has the required outputs, you just need a few capacitors and the S-Video connector.
You can use the CD32 schematics as reference, the correct circuit is depicted there. |
Thanks for the warm welcome. This is my first DIY hardware project that works :D.
I just cleaned up the schematic, be warned that it is a large image. This configuration is NTSC only. The AD724 can be configured for PAL by tying STND to ground, but it also requires a 4.43 MHz clock input at FIN. NTSC Amigas do output a 3.58 MHz clock which works for NTSC, but a PAL Amiga outputs a 3.55 MHz clock. You would need to multiply the 3.55 MHz clock by 5/4 or supply a seperate clock crystal for PAL operation. |
Would it be to difficult to do a version that works with pal and ntsc amigas? With some kind of mini-switch doing the change from ntsc-pal?
Best Regards Rod |
It is possible to make a ntsc/pal switchable version, though you need to add a clock crystal for pal operation (the amiga sources a proper clock for ntsc). The switch would have to switch the clock source, and toggle the STND line on the AD724 chip to change between ntsc and pal.
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Hi, im considering doing this mod but building it into the inside of the amiga, where did you buy the ad724 chip? ive checked my local place that i usually buy from "Rapid Electronics" but they dont seem to stock it, is there anywhere i could pick up a free sample of this chip?
EDIT: Also, on your schematic is pin 1 of the video conector at the amiga end, the pin with the box round it? |
I could not find any samples for the AD724, so I had to buy it ($14 CAD, ouch). I got mine from Newark, but I don't know if they ship to the UK. Regarding the schematic, pin 1 is the pin with a square around it.
The pins are numbered top down, so pin 1 is at the top left, pin 12 at the bottom left, pin 13 at the top right, and pin 23 at the bottom right. You should take a look at the data sheet on Analog Devices' website. There is an example schematic which shows how to connect a clock crystal (you will need it for PAL operation). BTW, are you planning to put this in your A500+ (mentioned here)? I just got a A500+ motherboard in the mail, but it has a PAL agnus :(. |
Yes i am planning on putting it in my A500+ , i have a series of mods planned for it, im going to eventually run it through the tv card in my computer that is when i can actually install the tv card stupid windows. yeah im slowly but surely fixing that damn A500+ i like the idea of the ReloKick that someone suggested im also considering buying a catweasel PCI card for my computer when ive finished working on the amiga.
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Neobitz in my A1200
Here's the neobitz s-video board installed in my A1200. An s-video port is mounted on the back door plate (where the scsi board would be installed). Easier to replace the plate than the case to make it original again.
http://www.floridakitesurfer.com/amiga/svideo.jpg |
is there a link i can get this neo-bitz kit from ?
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The Neobitz page. It hasn't been updated in over a year, and I did not get a response to the email I sent asking if they still sold kits. That's why I had to build my own board. Fortunately there is a parts list for the kit on the site :).
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would the kit work for PAL ?
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That kit needs to be modified to work with PAL. You need to replace the included 3.58 MHz crystal with a 4.43 MHz crystal, and you need to modify the PCB so that the STND signal (pin 1, I believe) is connected to GND instead of +5V. That should be all that is needed.
I'm considering making a PAL version for my A500+ because it cannot be modified easily to be NTSC. I'll update this thread if/when I do that. |
@narmi, you sir are indeed a saint!
if its okay, I will re-develop the board in pad2pad, with the suggest modifications, if I post it here, could I be so bold as to ask a check-over ? |
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Just thought i would add this simple board type for consideration and revision,
I am using pad2pad wich is free and easy software to use. (its because i am cheap i tell you!) I havent labled up the caps / resitors etc its just a foot print and is virtually identical to the neobitz board (i have removed the expansion area) anyway pointers are more than welcome. |
There are some connections missing on your layout. The Neobitz board is double sided, so some of the connections are on the back. I'm working on a layout using EAGLE. EAGLE is also free, but it's not very easy to use. I'll upload my project files when I'm done.
I think it is possible to make a single sided board, perhaps with one or two jumper wires. I'll see what I can do. |
Thanks Narmi,
would you have a picture / schema of the back ? |
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I've finally finished creating the schematic and PCB layout in EAGLE, and uploaded it to my webspace. I managed to get all of the connections onto one layer without any jumpers. However, with all the deleting and redoing of tracks, I buggered up the project file, so the software thinks that the board layout and the schematic do not match.
Depite that, I did make and etch one board. I still need to buy a crystal before I can test it, but I did a quick visual check, and all the connections seem to be correct. I've attached a low-res picture of the board layout. You can use that as a reference to make your own layout in another program. BTW, I have not used the big 470uF capacitor used on the neobitz board. I don't think it is necessary, but it would help to reduce noise from the power supply. Leaving it out reduces the board size and the parts cost (yep, I'm cheap too :D). |
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