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gary wrote:
Yes but what I was trying to do was get to the bottom of why the syncs are so long - pretty hard to do when they are not there! LOL
basically what I am trying to do is get to a stage where we have a black picture - i.e. no video signal - but even a black picture needs syncs.
The trick is we are trying to get the output of the mixer at 1vpp - with the sync portion being .3V - so a black picture will be .3vpp - once we have that we can add video - step by step, inch by inch.
yes but it will be useful if we have to look at other parts of the cct besides the output.
Anyway you can inject the sync pulses is fine for these tests Harry - no need to use my suggestion if you have an easier way.
BTW I just want you to realise that the height of the sync pulses from your monostable will have nothing to do with the height of the pulses coming out of the mixer - they need only be enough to saturate Q1 on and off (like a switch).
gary wrote:Oh that looks very plausible except you have the wrong monostable output - we want positive going pulses (because that's what comes out of PD1).
gary wrote:The scope grabs were good but when you invert the syncs I would like to see a wave file as well if possible.
gary wrote:Ok that's looking better (except the noise) - please be aware that you are recording inverted now that the syncs are the right way up - oh well that's fairly normal - you always have to be aware that the recording can be inverted when recording into a pc.
It appears that you have your volume control for recording ratcheted up to a spine tapping 11 - you should back that off to about a Lawrence Welkian 6-7.
gary wrote:You are using windows right? All Windows Os's have a mixer (or one that can be installed) and that's all you need - let me know if you want me to walk you through it.
gary wrote:That's an odd thing Harry your video is drifting even faster than the sync - so something appears to be awry with your video source.
But you have me confused now because I thought that both your test video AND your sync pulse are generated electronically - so how could the pulley belt affect things?
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