Author Topic: Getting a useable video signal out of a PCW  (Read 1696 times)

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Offline JonB

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Getting a useable video signal out of a PCW
« on: 17:13, 05 January 17 »
While I wait to fix my 9512 power supply, I have decided to hook the processor board up to a composite monitor (well, a TV to be precise). I have video, GND and sync on the CPU card. The picture is being generated from Video & GND (via a composite input), but it flickers all over the place and the TV is unable to lock on. Probably due to no synch! Anyway, what's the easiest way to connect it? I could combine for composite, or use a SCART input..? If so, how?

Offline 1024MAK

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Re: Getting a useable video signal out of a PCW
« Reply #1 on: 17:39, 05 January 17 »
If the video signal and the sync signals are at normal standard levels (check with a 'scope), feed the video to the green video channel on a SCART input, the sync to the composite/sync input, and ground the red and blue video inputs.

That should give you a green screen display  :P

Mark

Looking forward to summer in Somerset :-)

Offline JonB

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Re: Getting a useable video signal out of a PCW
« Reply #2 on: 19:05, 05 January 17 »
Well, Mark.. Seek and ye shall find: http://www.amstrad.es/forum/viewtopic.php?f=35&t=2480


* IMG_0661.JPG
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A close up of the "board". Just a 7400, resistor and variable resistor. Plus a bunch of jumpers (and two resistors that aren't needed).

 [ Invalid Attachment ]


Gotta love that breadboarding kit..


Now, the signal is a little bit noisy. Not sure why, but I guess it is due to not having shielded signal cables between the PCW and the board.
« Last Edit: 19:29, 05 January 17 by JonB »

Offline 1024MAK

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Re: Getting a useable video signal out of a PCW
« Reply #3 on: 22:14, 05 January 17 »
To reduce noise, you may need to do a number of things:
  • As you say, used screened cable, braided is best,
  • Add some decoupling capacitors (say a 10uF to 47uF and a 100nF) near the chip,
  • Add a filter (resistor, say 10 to 68 ohms and a RF choke / inductor) in series with the +5V supply to the chip,
There may be some other things, but I have not studied the circuit.

Mark
« Last Edit: 22:20, 05 January 17 by 1024MAK »
Looking forward to summer in Somerset :-)

Offline Bryce

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Re: Getting a useable video signal out of a PCW
« Reply #4 on: 22:22, 05 January 17 »
The breadboard will be the main source of most of that noise. On a real PCB the noise would be greatly reduced.

Bryce.

Offline JonB

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Re: Getting a useable video signal out of a PCW
« Reply #5 on: 22:31, 05 January 17 »
I'm gonna put it on stripboard then.


Just glad it worked (first time, heh!). I'm running it off a nasty little Chinese power supply though. It's only temporary, I hope to fix the 9512's power supply board soon...


Cheers
JonB

Offline Bryce

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Re: Getting a useable video signal out of a PCW
« Reply #6 on: 22:36, 05 January 17 »
Then cut through all the over-length copper strips after it's soldered up and as 1024MAK said, decouple the IC with a 100nf cap as close to the power pins as possible, a 100µf cap across the power lines where they enter the circuit and coax type screened cable for the signal connections (or at least twist the cables).

Bryce.

Offline JonB

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Re: Getting a useable video signal out of a PCW
« Reply #7 on: 15:05, 06 January 17 »
Something like this then..


[attachimg=1]


JP1 needs to be connected to +5v on the 9256 PCB.
JP2 plugs directly into the video pins of the 9256 PCB.
Yellow is Video, Green is Sync, Red is +5v, black is GND/0v.
VR1 is 10k (bigger than the schematic, but works).
R1 is 1k.


It's about as small as I could make it, to keep signal paths short.

Offline Bryce

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Re: Getting a useable video signal out of a PCW
« Reply #8 on: 15:33, 06 January 17 »
Yes, except C2 should be a ceramic 100nf capacitor.

Bryce.

Offline JonB

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Re: Getting a useable video signal out of a PCW
« Reply #9 on: 16:06, 06 January 17 »
Can I use 220nF?

Offline Bryce

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Re: Getting a useable video signal out of a PCW
« Reply #10 on: 16:09, 06 January 17 »
It's a bit on the high side but it's better than the 47µf.

Bryce.

Offline JonB

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Re: Getting a useable video signal out of a PCW
« Reply #11 on: 17:57, 06 January 17 »
Eventually....



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I managed to put the connector block on the wrong side of the board, so had to turn it upside down, and build a spacer for the block.. duh..


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Even so, picture quality is acceptably good.


 [ Invalid Attachment ]


Now just the serial port to go (Audronic is sending one  8) ) and I can begin IDE driver development. Then the PCW can get some love.
« Last Edit: 18:08, 06 January 17 by JonB »

Offline Bryce

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Re: Getting a useable video signal out of a PCW
« Reply #12 on: 23:14, 06 January 17 »
Is all the noise gone?

Bryce.

Offline JonB

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Re: Getting a useable video signal out of a PCW
« Reply #13 on: 00:19, 07 January 17 »
Yes, mostly.  :)


Thank you both for your advice!



« Last Edit: 00:21, 07 January 17 by JonB »

Offline 1024MAK

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Re: Getting a useable video signal out of a PCW
« Reply #14 on: 00:40, 07 January 17 »
No problem  :D

Glad you got it working to your satisfaction  ;D

Mark
Looking forward to summer in Somerset :-)