Negative voltage at GPIO pin

[cwford]

Measuring RPMs of my boat's engine via PWM from the alternator. Current circuit design gives me -12 millivolts at startup/idle but no negative voltage in normal operating RPM range. Is -12 millivolts still too much negative voltage at an ESP32 GPIO pin?

Understand that negative voltage at a GPIO pin can damage an Esp32. But how much negative voltage is too much? Can't seem to find any specs on that.

TIA,

Clyde

[Sprite]

Is -12 millivolts still too much negative voltage at an ESP32 GPIO pin?

That's in the datasheet. You didn't specify what ESP32 you have (so make sure to check the datasheet for your specific chip) but generally voltages down to -0.3V are acceptable.