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Old 18th Apr 2019, 12:52 pm   #80
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by DonaldStott View Post

NOTE - still no responses to my Post #54 above.
Just so you know you're not being ignored, the only observation I would make about that is that the vertical display looks rather odd, in that it makes the square wave look 'dovetail' shaped. Ordinarily, if the bandwidth of a scope is low, the 'risetime' will be slow and will be noticeable towards the limit of the scope's bandwidth. With a slow risetime the upward strokes of the display can slope forwards, (and the also the down strokes), but at such a low frequency of 300Hz, even on a scope with a low bandwidth the waveform should be square. I've annotated your picture in yellow to show what I mean.

I don't think it's due to the angle at which you took the picture (with your camera sloping downwards rather than square on to the screen) because the lines on the graticule look vertical. More like to be the adjustment of the scope or the way that the pic was taken than the strobe circuit because another cycle can't of course start before the preceding one is finished. If it does, you've invented a time machine not a strobe!

I've just taken a pic of a square wave on my own scope to show what it should look like.

Explanation of risetime: https://www.youtube.com/watch?v=eRA1Mx506fw

Hope that helps a bit, though it's no help in getting your strobe circuit to work as you wish it to, so good luck with that.
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