Amiga RGB to S-Video + composite adaptor

[narmi]

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.


The circuit is virtually the same as the one in the AD724 datasheet, not too many connections as you can see from the bottom.



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.

[Shoonay]

Cool!
Looks nasty-soldered but it's what I like in home-made stuff

[Zetr0]

@Narmi


Welcome to the EAB, i am sure you will like it here

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 ?

[Jope]

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.

[narmi]

Thanks for the warm welcome. This is my first DIY hardware project that works .

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.

[Rod_cl]

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

[narmi]

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.

[fool2cool]

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?

[narmi]

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 .

[fool2cool]

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.

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.

[Zetr0]

is there a link i can get this neo-bitz kit from ?

[narmi]

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 .

[Zetr0]

would the kit work for PAL ?

[narmi]

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.

[Zetr0]

@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 ?

[Zetr0]

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.

[narmi]

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.

[Zetr0]

Thanks Narmi,

would you have a picture / schema of the back ?

[narmi]

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 ).