Amiga RGB to S-Video + composite adaptor

[amigamaniac]

Ahhh, I nearly forgot about this project...

I've decided I'm going to make an RGB to PAL/NTSC Composite and S-Video out adapter myself. Reading the data sheet of the AD724, it seems pretty straightforward. They provide the schematic, with even the switching circuit between PAL and NTSC! So all I have to do is follow their instructions, and use my wee brain here and there to fill in the gaps, and solve any problems that may arise.

Features I hope to include:

* Plugs directly into the back of the 23 pin D-sub on the Amiga
* Switchable between PAL and NTSC with the flip of a toggle switch (if it's in a small case). Otherwise a jumper on the PCB.
* Has two outputs: composite, and S-Video

And of course, I hope to offer it at a super cheap price, in line with my other home brew gear

I've ordered some AD724's from my supplier along with the EPROM's and ZIP RAM (the usual crap), so I can start experimenting/prototyping.

I'll let you all know how I get on...

Weeeee, a new project!

[amigamaniac]

Hi All,

Ok, I made a prototype following the schematic provided by Analog Devices from their data sheet for the AD724. I made a PAL version, with the correct crystal etc, as I live in Australia.

It works fine (composite out), with only a little noise (dot crawl mostly I think), which is to be expected since it is not a propper PCB design with a nice ground plane etc.

However, when I connect the S-Video plug, the picture looks fine, but rolls vertically on the TV screen. I'm plugging it into my DVD player, and I tested the S-Video input with something else, and that worked normally, so it's something to do with the prototype.

Does anyone know whats going on? I'm worried that if it doesn't work correctly with my prototype on the S-Video out port, then it won't work properly on my PCB design either. I was hoping that a nicely designed PCB would clear up the problem...but perhaps that's a gamble that is not worth wasting a couple hundred dollars

Oh, and Zetr0, I'm wondering if that 74LS08 IC will correct the problem somehow? I was trying to work out why you had that on your schematic above. It also looks like you got the pins mixed up on it too Same with the AD724 - pin 9 in Chroma, pin 10 is Composite, and pin 11 Luma.

I have tried connecting the AD724 to H-SYNC and V-SYNC, and also the C-SYNC only method. All with the same results.

Any advice? Once I solve this problem, I can design the PCB's. I'm guessing that the adapter may only cost about AUD$30 fully assembled

[kipper2k]

Hi,

I just finished converting a A600 to have a SVideo output. I removed the old RF box off the motherboard, drilled a few holes in it, placed a SVideo edge connector on it and then connected it up to my little SVideo circuit i built using Chroma/luma from the onboard video chip. (I'm still waiting for my prebuilt boards, but i got impatient). Anyway, for the signal out i used a 100ohm pot and found (in my case) that 75 ohms was too high a resistance which made the brightness too low.
BTW, i used all surface mount resistors to reduce the physical length of the circuit so i'm not sure if that helped with the quality of the picture or not.
I rate the SVideo picture when comparing it to a 1902 picture as a 8.5/10. the picture is really nice but there is some tiny artifacts which although barely noticeable make me want to try to make it better.

The circuit i used was the one that people used to mod their Sega Genesis and works quite nicely

heres that link...

http://www-unix.ecs.umass.edu/~dhowl.../#buildingamps


The best value i found for the output resistance was 39 ohms so maybe try using a pot and see if that clears up the picture a little. I'll post some pictures later... my apartment got flooded out this morning so i have to abandon all my toys for a few weeks while i am in temporary digs

I'll order the parts for this project and give it a play,


BTW Nathan, my thoughts on the rolling could be thecrystal out of sync ?

is this the AD724 you ordered ?

http://search.digikey.com/scripts/Dk...me=AD724JRZ-ND

[kipper2k]

C4, C5 and C6 are stated as 220 micro farad caps, is that value right?, i cant find anything of that value at my fav haunts. Are they ceramic ? Any links etc would be welcome

Thanks

nm, looks like its gotta be a Tantalum

[Zetr0]

@Kipper2k

Hope you get some new digs soon m8... never liked that flooding stuff... always messes things up!

okay yes the 10U (C8) is a tant

C4,5,6 are standard electrolythic 220U signal cleaning caps

C7 is not needed

C's 1,2,3 and 9 are all mono's

the 74LS08N is the wrong IC , i will update the schematic for corrections lol

the idea behond the 74LS08N was to provide a higher signal strength drive so you can use a VGA cable, I must of got confused with the commodore referece... its been a while

The rolling could be a power issue, have you checked the amps?

[amigamaniac]

@kipper2k

I am using AD724JR, which is the non-RoHS component I believe. I can get them *much* cheaper than that - I get them from my supplier. I'm not really interested in modding my Amiga's to get S-Video for myself, but more interested in provding something that people can just plug in and use. Not everyone is good at, or can solder etc

@Zetr0

So you think that 100mA is too much current for the AD724? I am powering it from the 23 pin D-Sub, pin 23, which is only +5v @ 100mA. Do you think I need a V-reg or something? Or would a resistor do? I''ll have to read the datasheet yet again, to see what current it asks for (max). I just assumed it would happily function off the current provided by the Amiga video port. I'll try reducing the current, and see what happens. Maybe there is a groundloop somewhere in my circuit, but I doubt it.

I've also compared the composite out of the Sony chip built into my A600, the Motorola in the A520 (which are still available from Futurlec!) and the AD724. AD724 looks the worst IMHO - but this could be due to my rough prototype board layout, which will always be less than ideal I suppose.

[rkauer]

Pin 23 of RGB connector already have an internal SMD resistor for limiting the supplied current. Better put a little ceramic capacitor on the external to decouple voltage ripple on the +5V line.

[amigamaniac]

@rkauer

Yeah, power on pin 23 is already limited - to 100mA. The data sheet of the AD724 recommends an input current of between 33mA and 42mA. If I add a 130 ohm resistor at the +5v line on my prototype board, it would cut the 100mA to approximately 38mA, which is within the specified range I could then decouple that with a capacitor I suppose. However, since both the APOS & DPOS on my prototype board are both decoupled as per the AD724 data sheet, perhaps this is not really necessary. Having the extra filter cap at +5v can't hurt though I suppose. I'll see what happens...

[amigamaniac]

Ok, good news...

Adding the resistor to cut down the amps - bad idea. It made the AD724 totally non functional.

I left everything as it was before, except that I added a ceramic trimmer cap between the crytal and pin 3, rather than a regular ceramic cap. This allowed me to "fine tune" the circuit, resulting in a rock solid picture. I even played a couple of games, and was very impressed - and all this on my 68cm CRT TV from only 2ft or so away from it! Picture was clear, colours were normal and crisp. I then compared it to the Composite out supplied by the A600 (Sony chip), and couldn't really tell the difference. Not bad for a rough prototype This was all done on composite out from my prototype.

Now, in regards to the rolling S-Video, I decided to connect the prototype composite out to the DVD player, rather than directly to the TV - the picture then rolled. This means the problem is related to the DVD player! Unfortunately, my TV does not have an S-Video input It does have component-in though That means, my design is fine, and the picture would not be rolling if my TV had a S-Video input.

[amigamaniac]

Ok, I would like some feedback on the final design, and some other help - where can I get those freakin' PCB mount 23 pin female D-Subs?

I found some on these two sites, one in the U.S., and one in the U.K. Neither have answered my e-mails, and it's too expensive to call them. Does anyone from the U.S. or U.K. want to contact them by phone? Whoever helps me may get freebies, or in the least huge discounts, free postage/shipping etc :-D Look at my website and see if you want something: www.amigamaniac.com Or you can wait until I have the RGB to PAL/NTSC adapters made.

Here are the websites where the 23 pin D-Subs are (apparently):

http://connectors.keltronconnectors.com/viewitems/connectors-d-sub/ght-angle-8-08mm-footprint-stamp-pin-5504f1-series?&pagenum=2&measuresortid=0

http://www.westfield.co.uk/Powerand%20c2b%20connectors/idcsh/3013.htm

Regarding adapter design...

I was thinking to have the PCB plug directly into the 23 pin D-Sub, with no case. I would then have two holes drilled on the back corners of the PCB, for adding nylon spacers, so that the PCB would sit flat, and not "hang" from the socket. It would be narrow, and short, and not interfere with any other connectors on the back of the Amiga. Would anyone object to not having a case? A case means more work for me - drilling holes, and cutting out a rectangular hole for the 23 pin D-Sub socket. It would also add to the cost, by as much as AUD$5, depending on the case (could even be more). Having a case would also require a switch for selecting NTSC/PAL, further adding to the cost. With a bare PCB, a simple and cheap jumper block would suffice.

For NTSC users, no NTSC crystal would be needed, as the correct clock comes from the video port. This keeps cost down. It WILL have a PAL crystal however, so the user will be able to select NTSC or PAL by simply moving a jumper on the PCB.

I could make it case optional, no case, or case only. Any thoughts? What would you prefer? Personally, I don't care about fancy cases, I want something that is as cheap as possible that works - but that's me. I'm thinking case optional, to keep everyone happy I actually prefer a naked PCB to look at, always have

So at the end of the day, I'm going to make the RGB to PAL/NTSC adapters. I can design the PCB in a day, and have the PCB's in about 3 weeks. I'll have about 50 of them made. Other components are no problem to obtain, except perhaps for the 23 pin D-Subs They will be sold fully assembled and tested only, no kits. I'm aiming for a target price of about AUD$30.

[ethylene]

amigamaniac, I tried calling the Keltron company using both their listed numbers. Both play a message stating the number's disconnected. Sorry about the luck

...What about Part #2100-023S at pimfg.com? I called and verified--200 in stock.

[kipper2k]

Originally Posted by amigamaniac

Ok, I would like some feedback on the final design, and some other help - where can I get those freakin' PCB mount 23 pin female D-Subs?

I found some on these two sites, one in the U.S., and one in the U.K. Neither have answered my e-mails, and it's too expensive to call them. Does anyone from the U.S. or U.K. want to contact them by phone? Whoever helps me may get freebies, or in the least huge discounts, free postage/shipping etc :-D Look at my website and see if you want something: www.amigamaniac.com Or you can wait until I have the RGB to PAL/NTSC adapters made.

Here are the websites where the 23 pin D-Subs are (apparently):

http://connectors.keltronconnectors.com/viewitems/connectors-d-sub/ght-angle-8-08mm-footprint-stamp-pin-5504f1-series?&pagenum=2&measuresortid=0

http://www.westfield.co.uk/Powerand%20c2b%20connectors/idcsh/3013.htm

Regarding adapter design...

I was thinking to have the PCB plug directly into the 23 pin D-Sub, with no case. I would then have two holes drilled on the back corners of the PCB, for adding nylon spacers, so that the PCB would sit flat, and not "hang" from the socket. It would be narrow, and short, and not interfere with any other connectors on the back of the Amiga. Would anyone object to not having a case? A case means more work for me - drilling holes, and cutting out a rectangular hole for the 23 pin D-Sub socket. It would also add to the cost, by as much as AUD$5, depending on the case (could even be more). Having a case would also require a switch for selecting NTSC/PAL, further adding to the cost. With a bare PCB, a simple and cheap jumper block would suffice.

For NTSC users, no NTSC crystal would be needed, as the correct clock comes from the video port. This keeps cost down. It WILL have a PAL crystal however, so the user will be able to select NTSC or PAL by simply moving a jumper on the PCB.

I could make it case optional, no case, or case only. Any thoughts? What would you prefer? Personally, I don't care about fancy cases, I want something that is as cheap as possible that works - but that's me. I'm thinking case optional, to keep everyone happy I actually prefer a naked PCB to look at, always have

So at the end of the day, I'm going to make the RGB to PAL/NTSC adapters. I can design the PCB in a day, and have the PCB's in about 3 weeks. I'll have about 50 of them made. Other components are no problem to obtain, except perhaps for the 23 pin D-Subs They will be sold fully assembled and tested only, no kits. I'm aiming for a target price of about AUD$30.

Hi Nathan,

I'd like to be the first on the list for one of these puppies.

... Hmm, make it 2. Makes the games so much more enjoyable when it looks good on the screen.

I also went looking for the 23 pin connectors, i managed to find 4 on ebay, they are getting tough to get. A poor substitute could be a modified 25 pin connector that is keyed so it will only plug into the correct pins, it will work good. A dremel will shave off the end row top and bottom and prevent users from plugging it in incorrectly. Want me to start my Dremel! If you want me to mod some 25 pin connectors i can buy em, crop em and mail them to you and get a discount from you. It takes 4 days for Digikey to deliver the pieces to me and 2 nights to chop em depending on the amount.

[amigamaniac]

@ ethylene

You are a GOD to me now! I've e-mailed the PI people, as there is no allowance for international orders at checkout Once I have secured my purchase, I will reward you somehow for your efforts I received an e-mail from Keltron, they have a minimum order value of USD$250. I actually remember browsing that PI website last year. I don't know why I didn't add it to my favourites, silly me.

@ kipper2k

That's a generous offer mate, thanks I already considered such a thing myself, but would prefer the genuine article - the super rare 23 pin D-Sub. I could do a hack job of 25 pin D-Subs myself, if I needed to.

I'll do my best to get this project finished a.s.a.p. - and this WILL happen, as per my other projects (ROM switchers). I'll update as new developments occur

[Zetr0]

there might be an easier way guys...

in my proto designs I used a 23pin D sub (non pcb mount) in a non-so-standard way.



it works, just needs some good lining up

[amigamaniac]

@ Zetr0

He he, you naughty boy I forgot about that method! That will be a last resort. I should be able to obtain the right angle parts.

I'm all excited now, as this project will actually be a reality soon!

[Zetr0]

Good luck with it my friend,

let me know if theres anyway i can help

its a damn pity you live the otherside of the plannet, I have about 4 right angled 23pin D subs you could have for your proto's!

[Zetr0]

Hmmm i could give Westfield a buzz for you in the morning m8, see what they can offer you.. if needed i could act as intermediate shipping if they dont do international.

[amigamaniac]

@ Zetro

That's nice of you! Flamin' Westifield are rude. Didn't bother to answer my e-mail of over a week ago. I sent them another one the other day.

I have finished my prototype already, it's actually my second one. First one was very messy, and I got the caps the wrong way around on APOS and DPOS, so the picture was terrible. There was also wire everywhere - great for picking up even more RFI, crosstalk etc. In the first prototype, I used the switching circuit for PAL/NTSC from their data sheet, even using the HC04 IC. Worked fine, but I don't really need it, since the correct clock comes from an NTSC Amiga. Saves money and components! A simple jumper will do the trick.

My second prototype has only the PAL crystal, and no selection. I kept it as simple as possible. I used a genuine 23 pin female D-Sub with backshell to connect it to my Amiga. I should upload a photo of the prototype. Also two photos of the TV screen - one of composite out, and one of S-Video out. I have a second DVD player with S-Video input that I can try. Hopefully the image won't roll when the Amiga is plugged into it...

[Zetr0]

ahhhh talkings of hardware pr0n is like music to my ears my friend!!!

I would love to see .... hey taling about crazy proto's you will have to ask TheCorfiot about the 27C4001 to 27C400 adapter i built.... it works..... but my GOD is it ugly!

[ethylene]

@ Nathan

Happy to help!