LM393 Dual Comparator- Interferance

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Joined Nov 6, 2018
EDIT: Sorry- I resolved the issue, made a CAT-5 cable and changed the pairs around in the RJ45 to pair each signal with a ground or 5v0 line and the issue dissapeared. Wasn't able to see any voltage fluctuations on my o-scope but i guess something was still happening with crosstalk

Hey everybody. I have a circuit using 2 LM393 Dual Differential Comparators as shown in my schematic. My problem is that there seems to be some interference issues in my circuit. Each input is setup on a hall effect flow sensor, and only reach about 30hz square maximum.

  1. When Input 1 of a comparator is High and the second input oscillates then both outputs oscillate causing the microcontroller to show that water is flowing through both sensors instead of just #2.
  2. Same happens vice versa is Input 2 is high and the first input oscillates then both outputs oscillate .
  3. Very little happens if one input is low and the second oscillates, occasional noise but the software easily filters this out.

In trouble shooting iv'e checked:

  1. impedance between all inputs and outputs and find them all to be within the expected impedance's.
  2. Ive used my oscilloscope to see if the problem was on the inputs, however; voltage stays steady to within a couple millivolts on the steady input while it's output is oscillating along with the second input.

Also it's not noted on the schematic but the input is a squarewave 0v0 - 5v0. The signal is carried over a CAT-5 cable that in honesty isn't optimal as a twisted pair is carrying 2 signals(however, not the signals that are having correlation with each other) And with the oscilioscope i don't see much reason to suspect cross-talk especially as the fastest the sensors transmit in my application is roughly 30-40hz. Comparators.png
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