Built my own: Amiga RGB to S-Video + composite adaptor small issue though...

[waltermixxx]

Hi there, I built this project (picutres to come) on a vero PC board with a 15 pico farad capacitor, and the NTSC colourburst crystal (3.795 etc Mhz)

I am not getting any colour from either the Composite out, or the Svideo jack. I'm guessing, from what I have read on the "Amiga RGB to S-Video + composite adaptor" thread that the capacitor might be the issue.

If the issue was just the svideo jack then the problem might be the chroma out put, ( bad connection etc ) but seeing as it's on both the composite (generated in chip) and the svideo, I'm guessing it's a timing issue with the crystal and capacitor. I will try a 20 pf.

If I need a variable one. what would be the best value to purchase?...

[Zetr0]

@walter

I think you need less than 15pf, firstly try it without a capcitor, and then *maybe a 10pf unit.

[waltermixxx]

he he, I was going to... one of the posts mentioned no cap at all
i was going to start with that... i have a bunch of small ones to try as well,
but a variable would allow me to fine tune incase it changes with another monitor...
but I suspect a a 0 to 20 pf would be good

thanks for your reply, I will post pics once I get it sorted out...

Cheers

[Retrofan]

Didn't you find more smilies ?

[waltermixxx]

It's a sickness,

you should see my emails at work, not sure when it started,
but but I usually have to go through my emails before I send them
to remove extraneous smiley faces...

luckily it only manafests itself in the written medium...
otherwise folks might think I'm meniacle.

Cheers

[waltermixxx]

This is the one I built on a vero board.
it did not take very long to do, and I used a SOIC to 16pin dip
adapter to make the process a bit easier...

Digi-key has both the chip (for around $11.00 canadian) and the soic adapter... ($6.00) so together a little hefty, but fun to build...

I will remove the 15 pf cap and see what happens

[waltermixxx]

Well now I am depressed... I could not find a cap that would allow it to sync up to this little LCD monitor... the picture remained in black and white, but I had issues with that monitor before... so I hooked it up to my 32" LCD HD tv, via svideo, and the blue signal came through fine, but the red and green looked odd. I tried various caps with that tv and either got black and white or a picture with messed up colours... I did verify my red blue green where going the appropriate pin n the chip, hsync and vsync appeared to be fine as I was getting a picture...

by the way I was testing this with my Atari 1040STE, I will have to fire up the Amiga 500 and see what kind of luck I get with that...

[Zetr0]

@walter

I noticed you have adapted the design with the addition of an LED, now the Amiga +5 on the Video out is 100mA (at maximum), the AD724JR requires a minimum of 42mA - its quite likely you are not providing enough power to run both devices.

[pandy71]

LED can be low power type - draw like 3 - 5mA - not a problem, IMO best is use +12V and some voltage regulator IC (it gives cleaner supply)

[Stedy]

Waltermixx,

Disconnect your 3.57 MHz crystal and use the NTSC carrier clock from pin 15 of the RGB port. This will be time aligned with the sync pulse edges, important for good colour definition (if possible with NTSC).

Have you ensured that pin 1 of the AD724 is pulled high to select NTSC encoding?
Is pin 12 pulled low to select FSC (3.57 MHz) clock input?

Normally a black and white picture is a result of an incorrect carrier frequency.

Ian

[amiman99]

Originally Posted by waltermixxx

by the way I was testing this with my Atari 1040STE, I will have to fire up the Amiga 500 and see what kind of luck I get with that...

I have seen few people, and myself, having trouble getting STE to sync up to RGB monitors like 1084 and RGB composite converters. The sync in Atari is not as good as Amigas. I would try on Amiga first.
The black and white problem, looks like is related to color carrier between PAL and NTSC as stated above by others.

[Zetr0]

@Walter

Sorry, I have to admit I am a little confused - you say you have been using this on the Atari 1040STE?

Video Pin-Out

1 - NC - *Audio Out
2 - Composite Video
3 - NC - GPO
4 - M detect (if low *grounded* ST enters Hires Monocrome video mode)
5 - NC - *Audio In
6 - Green
7 - Red
8 - +12V (520ST has GND here)
9 - Hsync - Horiz sync
10 - Blue
11 - NC - Monocrome Video
12 - Vsync - Vertical Sync
13 - Ground

Where are you sourcing your +5v ?

Are you sure you are outputting 60Hz refresh and not 50Hz Vertical refresh?

heres an alternative to an external SVideo output - should the 1040STe have a modulator then you can source the Chroma and Luma from there

here is how to do it


also might be relevant is this link Alexh put up a while back; an Atari ST SVideo Adapter - it still needs a little work but have a look it might help.

I will say that it does sound that either

1. the video signal is IN mono mode
2. the colour clock is no functioning properly (oscillator and or Ad724 setting)


Good luck with your investigations, let us know how you get on =)

[waltermixxx]

hi there, wow I appreciative of all the replies... thank you.

I am using it with an atari STE, mono detect line is floating so ST produces colour out.

I do have an amiga 500 I will try with as well, just to make sure it's not the circuit, as someone suggested that would be a good idea. I will post my findings... the Amiga does make it easy by providing a clock for the circuit... ( If it works with the amiga, I will remove the crystal and use it with my amiga, and perhaps doe the svideo mod on the ste.

I do have an atari colour rgb monitor, I was just hoping to use an LCD monitor as it's lighter and uses less electricity...

I was thinking of doing the Svideo mod to my 1040ste as it does have a modulator,
or simply using the composite video out on pin two of the 13 pin din, but the crisp image provided by svideo a million times better I'm just afraid of killing my STE doing the mod...

the 5 volts is coming from a power adapter, a switching variety for use with a USB hub, it's rated at 1 amp so plenty of power there for the LED i checked the voltage with a meter while powering the circuit and it's still 5 volts.

I may get 5 volts from the 15 pin ste joystick port... that may help too...

I will post how it goes with the Amiga 500. Thanks again...







The two pin socket is where i tried various caps, 10, 12, 15, 18, 22, 30 pf.
I'm sure there is a magic number in there somewhere

[rkauer]

Where you found this lovely SMD-to-DIP adaptor? Me likes it!

[Jope]

Originally Posted by rkauer

Where you found this lovely SMD-to-DIP adaptor? Me likes it!

Originally Posted by waltermixxx

Digi-key has both the chip (for around $11.00 canadian) and the soic adapter... ($6.00) so together a little hefty, but fun to build...

--

[waltermixxx]

I have not had a chance to try this with my Amiga 500 yet but will post when I get to.

[Matt020]

Could you please post some screen shots?

[desiv]

The ST is known to (sometimes??) have problems with the AD724.

There's a thread on it on atariage in their ST section...

desiv

Found it:

Out of spec HSYNC signal, so AD72x and friends can't properly sync up.

From here:
http://www.atariage.com/forums/topic...ge__hl__svideo

[pandy71]

Originally Posted by rkauer

Where you found this lovely SMD-to-DIP adaptor? Me likes it!

just made own yourself - use this method http://www.dr-lex.be/hardware/tonertransfer.html and on less than 1hr you have own pcb.
It works but i prefer background paper (waxed paper) from laser printable labels/stickers

[Munchausen]

Sorry for grave digging but I have just built this circuit and I searched all over the internet for an answer to this and eventually figured it out so I thought I'd give an answer.

I don't know what capacitor you have in your circuit but in the datasheet it will give you a 'shunt capcitance' to be used with it, typically 18 or 22pF.

Now, the crystal needs this much capacitance in parallel, but you need a capacitor value such that the cap value + any latent capacitance in your circuit = the shunt capacitance.

On PCBs the latent capacitance is quite small, but with strip/vero board the linear tracks cause _much higher_ latent capacitance in your circuit, much too high for the crystal, so in fact you probably already have far too much there.

I spent days playing with this and was going a bit crazy. I then realised this, and cut all the traces in my strip board connected to pin 3/the capcitor to make them as short as possible (no left over strip that goes nowhere). Before everything was black and white and blurry whatever I did, now its in perfect colour! Also, you can use a little trim capacitor to tune it to the right value, or just try some different values. Now I cut the traces I even get colour with no capacitor present.

Probably you've forgotten this project a long time ago, but maybe this can help someone out!

[prowler]

Hey Munchausen,

Thanks for making the effort to join up and add that very relevant point to this thread.

It's very much appreciated.

[Munchausen]

No problem

There are a few similar posts around the interwebs where people have the same problem, but none found a solution, so hopefully I can save someone the pain I went through trying to figure this out!

[Johan1973]

I use this circuit, just add a svideo connector on the chroma and luma output, works a treat

[kipper2k]

Circuit is shown on the AD724 datasheet on page 10. Oscillator capacitor is 10 - 30 pf (i found 18pf ideal.

http://www.analog.com/static/importe...eets/AD724.pdf

[Munchausen]

Yeah, building the circuit itself isn't hard.

It's just that if you are using strip board you need to be very careful to keep the traces short or you'll get too much capacitance, the oscillator wont work at the right colourburst frequency, and you end up with a blurry black and white picture. There isn't anything about this in the layout considerations section of the AD724 datasheet.

You may need a much lower capacitance than the datasheet specifies due to parasitic capacitance in your circuit being higher.. I'm now using 4.8pF.

[jsr]

Hi!

I built that circuit in Narmi's topic, but i got a black and white screen. I have a PAL machine, so i put a 4.43 MHz oscillator between ground and FIN and connected STND to the ground to select PAL mode.
Any ideas why i got a bw screen?

[Johan1973]

Yes. I dont remember where it was, but I needed to jumper two legs on the IC together in order to get colour on pal. It has been long enough time that I dont remember much of that build. But I know I found the information in the datasheet, so I would recommend looking at that (for the AD724).

[jsr]

I already checked the datasheet but i did not found anything about it.
The pins wich are connected: STND/AGND/SELECT/DGND (these connected to ground) and APOS/ENCD/DPOS (these are connected to the +5V).
I think the pins you connected together were STND and AGND, but i already did too.

[Johan1973]

Jsr: modified mine to use Svideo out, connecting Chroma and Luma to a svideo connector.
Black and white colour is most likely due to you only getting luma signal out. Its late and I try to remember stuff that was long time ago. Sorry if I am not of much help.
The crystal must be a very specific 4.43 crystal with even the 4.43xx, xx numbers being important, to get proper video timing. If your black and white pictures are not distorted in any way, most likely that is not what cause it.

[jsr]

Thank you for helping. The crystal is on 4.433619 MHz.

[Johan1973]

That should do it.

If you followed the schematic precisely above, disconnect pin 1 on AD724 from Pin 15, and instead connect it to ground.

[jsr]

I already did that, STND is connected to ground.

[kipper2k]

It sounds like you have the PAL/NTSC selector backwards, thats why it is black, also you may have to change your capacitor value up a bit. If using it for PAL only you can remove the NTSC part of the circuit

[Johan1973]

(managed to make a time delayed double post, removed)

If you have an oscilloscope, it would be easy to check if you get chroma out at all.

[jsr]

klipper2k: The STND pin is grounded, PAL mode is selected.
I tried to put a bigger capacitor than the shematics said, instead of 15 pF i put in a 22 pF capacitor parallel to the oscillator. Still black and white and some weird noise (horizontal lines).
I tried it with a 27 pF one too, same result. The datasheet said 10-30 pF, maybe i need a larger than 30 pF capacitor for the oscillator?
I did not build the NTSC part of the circuit, there is only a PAL crystal and STND is permanently grounded.

Johan1973: I do not have an oscilloscope.
I use the composite output, did not mentioned this, sorry.

[jsr]

I uploaded my drawing to postimg, this is what i built:
http://postimg.org/image/jiw1nskcn/
The only modification to Narni's design, that this is a PAL circuit and there is no S-Video part, because my TV does not have S-Video input. And currently the capacitor beside the oscillator is not 15 pF but 27.

[jsr]

Okay, now it works, i checked the schematics of the A1200, and it's PAL oscillator had an 56 pF capacitor. I did not have an 56 pF one, but had two 27 pF, worked that too.

Johan1973, kipper2k: Thanks for the tips.