I am designing a PCB with a PIC 16 microcontroller. The purpose of the PCB is to measure the voltage of a button cell battery, before the battery is placed in its device (assume this battery testing is involved in a mass production line, so its used very much, and very quick). Now I am using a sort of clothspin to clamp the battery on the top and bottom side (anode and cathode). But the mistake to reverse the polarity of the battery is very easy to make. For that reason I want to include a reverse polarity protection, so that if the battery is placed wrong (negative voltage on the analog input) it doesn't fry my microcontroller. What is the best option I can use? A diode won't do the trick in my opinion since that makes the voltage that I want to read drop, but I also don't want to make a very difficult circuit for this RPP.

This is the circuit. The Battery wire is going to the analog INPUT. The resistor values are not right yet. They will be something like 100, 1000, 1000 ohm.

• A diode wont do the trick in my opinion since that makes the voltage that i want to read drop... Okay then what other device can you think of that prevents this? I contend that you can still use a diode and then design something the minimize this voltage drop. Also, can you explain why a voltage drop would be considered detrimental?
– user103380
May 14, 2020 at 15:49
• Im sorry, you are right. What i meant is: Just a series diode wont do the trick, because the voltage drop will be to big., so what kind of circuit can i use, with RPP, and minimal voltage drop. I am going to active test the battery 3 times, with 3 different resistors for very short periods of times. The current (and voltage drop of the battery) will be different each time. When the voltage drops, the analog signal will no be the same voltage as the voltage on the battery. And you might say, well, you know the voltage drop over the diode, but i got the feeling that this is not accurate enough. May 14, 2020 at 16:03