How does Arduino deal with negative voltage

Just wondering how the Arduino handles negative voltage..... Say you have -5V going into an analog input, how does it handle this?

The protection diode conducts to ground (all pins have a pair of internal diodes to keep the voltage between Vcc and Gnd, per chip spec). If the current exceeds 1mA (or was it 2? It's something really low), the chip may be permanently damaged. So you can only let it be exposed to a negative voltage if the source is high impedance, so less than 1mA will flow (and the pin would be just below ground, since the protection diode is clamping it). Generally speaking, you should avoid negative voltages like the plague in electronics. Very, very few devices will be happy if you apply a voltage to them higher than their supply or lower than ground (or below the negative supply for parts that have positive and negative supply) - you should assume they will not like that, unless otherwise specified.

(That said, it is okay to let the protection diode conduct small amounts of current, and in fact, Atmel has an app note where they connect a 120V AC line to a pin through a very high value resistor, in order to do zero-crossing detection.)

It cannot measure voltages below ground.

See the electrical specifications in the Atmega328p datasheet for more details.

jcorc:
Just wondering how the Arduino handles negative voltage..... Say you have -5V going into an analog input, how does it handle this?

Very poorly indeed! :astonished:

Magic smoke.

download.png

.

@LarryD Very nice mspaint(or similar) job.

-Malhar