Analog: Comparator Part II (publ. 2025-04-17)

I've had some trouble implementing my comparator using just op amps and the DG212B analog switches. In my tests, something strange is happening where the analog switches lock up after about a minute or so of use, i.e., they stop responding to the signals from the op amps. It is not quite the same thing as latching up, since voltage supply is not removed. However, if I cycle my +/- 15V power supply, then the problem does go away, at least for another minute or so. I think it is something related to capacitance, as I can sometimes unlock the analog switches by touching on the board with my finger. I wondered if maybe there was a loose connection somewhere but after further investigation I don't think so. I'm planning to build a simpler version of the circuit and do some more testing.

In the meantime I built a relay comparator, using another TQ2-5V electromechanical relay, which is working fine within its inherent limitations. I mainly wanted a comparator so that I could have the lower or upper bound of the solution shown more clearly on the oscilloscope display. E.g., in a falling object situation, 10V could represent the release position, and the ball would stop at 0V, representing the ground.

Here is a screenshot of the comparator chopping of the bottom half of a sine wave. The green line is the original signal.

screenshot of the comparator chopping of the bottom half of a sine wave

You can see there is some electrical noise when the relay switches, unfortunately.

Copyright

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