Triggering from + and - voltages

Projects General Guidance
1

Hi,

I need to trigger from a +2V and -2V signal. There is basically a +2V signal once a minute and a -2V once a minute that . The required output is to illuminate a LED output of around 5 seconds.

I can do the +2V trigger using a simple 555 timer that will turn on a LED for 5 seconds.

I'm not sure how I can trigger from a -2V signal to do the same thing.

Any help is most appreciated, thanks!

2

Arduino IO pins should not be fed negative V.

You could bias your signal, add 2.5V and look for < 1V and > 3.5V.

3

Optoisolator. Signal drives the LED. Output drives Arduino input.

4

You would need 2 optos.