The code is doing a digitalRead(PTT_SENSE), I'd expect the threshold on the nano to be somewhere between 1 and 2 volts
The problem is that when the +12v TX line into the LM78L05 at U3 goes to zero volts, the output of U3 remains up around 5v because there is no place for the charge on C150 and C151 to go. ?The pulldown resistor will eventually discharge those caps. ?The RC time constant of 0.2uF*20k = 4 milliseconds, which should be fast enough. ?I'd put that new 10k resistor from U3-1 to ground, rather than from A0 to ground, the latter case would reduce the maximum voltage into the Nano A0 pin down from 5v to 2.5v. ?This also reduces the RC time constant to 2 milliseconds.
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On Wed, Jun 14, 2017 at 08:28 am, Jack Purdum wrote:
Given your code, Allard, I'm surprised he needs a dropping resistor on that line.
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