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Old 10 April 2009, 02:47   #1
kjmann14
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S-video A500 Project (what Oscillator/Crystal to use?)

I'm working on making an S-video Board for the Amiga and ST Computers And I need to know what type of Oscillator to use for the Clock Signal.

This is for NTSC.

Can anyone help?
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Old 10 April 2009, 03:59   #2
Zetr0
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@kjmann14

this all depends on the video encoder you are using, if its a quad clock divisor or not.

what AD chip you gonna use?
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Old 10 April 2009, 04:32   #3
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@kjmann14

this all depends on the video encoder you are using, if its a quad clock divisor or not.

what AD chip you gonna use?
I'm Using the AD724JRZ
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Old 10 April 2009, 06:26   #4
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@kjmann14

you will need a 3.58mhz Osc or you could use the 14.32 pending on input level of the IC

heres my take on it for PAL



you will need to change the Osc for 3.58 for the ntsc colour carrier, dont worry about U2 in the diagram that is ment for something else, also there is no need for c7 capacitor

have a lookie at this thread http://eab.abime.net/showthread.php?t=30752 for a lot more info and discussion.
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Old 10 April 2009, 09:24   #5
haynor666
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Tell me, what for you need s-video for amiga? I think better and actually the best solution is use RGB. Of course in USA is rather hard to find TV CRT with RGB but after all you can use any old amiga monitors.
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Old 10 April 2009, 10:30   #6
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Fair points, FWIW:
-I find S-Video (almost) as good as RGB.
-It really opens up the connection options.
-It's cool to have...
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Old 10 April 2009, 10:53   #7
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Quote:
Originally Posted by Zetr0 View Post
@kjmann14

you will need a 3.58mhz Osc or you could use the 14.32 pending on input level of the IC


you will need to change the Osc for 3.58 for the ntsc colour carrier, dont worry about U2 in the diagram that is ment for something else, also there is no need for c7 capacitor

have a lookie at this thread http://eab.abime.net/showthread.php?t=30752 for a lot more info and discussion.

One Thing I would like to do is boost the RGB signals from 0.7volts to 1.0volts, But I don't want to do it inside the amiga. I would rather do it in the Circuit I'm Building.

Any Suggestions on how I would go about doing this?


=)
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Old 10 April 2009, 15:36   #8
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There is no match for rgb, s-video is poor and I only using it with N64 and 3DO and CD32 because I'm force to.
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Old 10 April 2009, 15:40   #9
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Quote:
Originally Posted by kjmann14 View Post
One Thing I would like to do is boost the RGB signals from 0.7volts to 1.0volts, But I don't want to do it inside the amiga. I would rather do it in the Circuit I'm Building.

Any Suggestions on how I would go about doing this?


=)
Low noise amplifier to provide the gain from 0.7 - 1V maybe?

Paul
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Old 10 April 2009, 19:21   #10
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Low noise amplifier to provide the gain from 0.7 - 1V maybe?

Paul

I wonder what amplifier would work well though. and how I would set it up.
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Old 10 April 2009, 20:17   #11
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@khmann14

you can use a 8703 tri-op-amp, have a look through the thread I linkied to as there are some references and sources on there
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Old 11 April 2009, 01:59   #12
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@khmann14

you can use a 8703 tri-op-amp, have a look through the thread I linkied to as there are some references and sources on there

Would Three 2N3904's work instead?

One for Each Color (Red, Green and Blue)
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Old 14 April 2009, 20:12   #13
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Hi,

@kjmann14

For NTSC you need a 3.579545 MHz crystal or oscillator with 10ppm or better accuracy. Some video devices require an oscillator with 10 ppm accuracy and 10ppm ageing, so check the datasheet for the intended part.
Ahh just checked, the AD724 is tolerant of oscillator accuracy. a 50ppm Crystal or oscillator will have a tolerance of +/- 178Hz on the colourburst frequency, 10ppm gives you +/- 35 Hz, for broadcast NTSC the tolerance is +/- 10Hz.

For the Video amplifier, you need an op-amp with a fast slew rate, at least 500V/us and low differential phase fain, typically 0.02%.

With NTSC video a single pixel lasts about 100ns, so you need an op-amp than can go from black level (7.5 IRE) to peak white (100IRE) and if ncessary back to black in less than 100ns. The Analog Devices AD8057 or AD8013 are suitable parts though there are many video amplifiers on the market.

The simple way to boost the video from 1V to 1.4V peak to peak is to use an op-amp with a gain of 1.4, be careful when increasing the Video levels from RS170A/RS343 level (0.714V signal, -0.286V sync) to RS170 levels (1V signal, -0.4V sync) as you may not get what you expect with some TVs. A lot of Analogue and Digital TVs use video decoder devices that have an Automatic Gain control circuit within and they do now work well with video signal greater than 1V peak to peak. The input decoder either attenuates the signal or sometimes it reduces the dynamic range of the input signal to fit, the end result is you loose colour information.

I recommend Analog Devices,http://www.analog.com for video parts as I have designed them into products in my day job, they work well. One tip, read the datasheet at least twice. It is not unknown for errors in their datasheets.

If you have any further questions, feel free to ask.

Ian
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