erik malund wrote:
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you can try this,
1) for a detector which need digital output, you need positive feedback (a resistor from the output to the non-inverting input). That will
a) make a scmitt trigger avoiding fluctuations between ok and not ok.
b) make a solid '1' or '0' on the output.

you mean the comparator with hystrasis, thats what my circuit diagram is.

2) when powering the op-amp with +9, you need to clamp the output or the uC pin will pop

if you see thoroughly the 5.6k pullup is connected to "+5V", and if you read the data sheet 339 has open collector outputs so out put will vary between 5V and 0.

abhishek