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Topic: Oscilloscope Modification (Read 874 times) previous topic - next topic

Collin80

#5
Jan 02, 2009, 05:02 pm Last Edit: Jan 02, 2009, 08:46 pm by AdderD Reason: 1
I'm curious... I recognize the normal voltage divider part of that circuit but why is there a 5v source and two 10M ohm resistors. What's that for? Seems like some sort of bias voltage.

It seems simpler to find the ratio between 12 and 5 and assume very low current draw. The ratio is 12/5. It might be safest, however, to go 12:4 in case of voltage spikes. In that case it's cutting the voltage to a third. That makes R2 twice the size of R1 which is easy enough to do. You can be pretty much assured of a low maximum current by using large resistors. Maybe 10k for R1 and 20K for R2?

Wait... I seem to recall that oscilliscopes need a really high resistance so that explains the 10M in line with the signal. Still confused about the 5V source...

walterr

I think there is a built in offset. The original post specified +-12V, so I think the offset makes -12v come in as 0, 0 come in as 2.5v and +12v come in as 5v.

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