I read that the Arduino analog pin should not go below -0.5 volts. In my project, I'm measuring cell voltages with the Arduino Uno. It occurred to me that I should protect the Arduino in case I accidentally hook up the cell to be measured in reverse (the battery voltages will be less than 5V). I tested the following circuit on a breadboard without the Arduino (ignore the periods). In case this crude picture doesn't come out right, it's a 100 kOhm resistor in series with the analog pin and a Schottky diode between the analog pin and ground.
Bat + ------100 kOhm ----|--------- A0 pin
.....................................|
.............................1N5819 Schottky
.....................................|
Bat - -----------------------|-------- GND
When the battery is in the right polarity, the voltage from A0 to GND is correct. When I reverse the polarity, the voltage is about - 0.25 V. The current draw is only 0.7 uA in the reverse polarity state. So this circuit looks like it would work to protect the Arduino's analog pin from reverse polarity. Am I not considering a potential drawback or is there a better way to do it? I'd like to keep the current consumption low. The batteries I'm measuring can range from 1.5 V alkaline cells to 7.4 Lipo batteries (with voltage divider).
Bat + ------100 kOhm ----|--------- A0 pin
.....................................|
.............................1N5819 Schottky
.....................................|
Bat - -----------------------|-------- GND
When the battery is in the right polarity, the voltage from A0 to GND is correct. When I reverse the polarity, the voltage is about - 0.25 V. The current draw is only 0.7 uA in the reverse polarity state. So this circuit looks like it would work to protect the Arduino's analog pin from reverse polarity. Am I not considering a potential drawback or is there a better way to do it? I'd like to keep the current consumption low. The batteries I'm measuring can range from 1.5 V alkaline cells to 7.4 Lipo batteries (with voltage divider).