# Detecting Open Circuit, Short Circuit and Battery Reversal

I am facing various design challenges with a project that I am currently working on.

I've been trying to figure out a way to build a circuit that detects open circuit, short circuit, and battery reversal. I am dealing with a battery assembly of six nickel-metal hydride battery cells in series which has a binder connector consisting of 7 pins (battery baton).

When the batteries are fully charged, the voltage is a maximum of 9V, however, in the event of the batteries being fully discharged, the voltage is 5V. I have found a way to eliminate reverse polarity as I can use a P-Channel MOSFET.

I am using an Arduino microcontroller to carry out pin checks between pins that may be short-circuited. In order to detect an open circuit (pins that are floating), I can possibly build a current monitor circuit that uses a shunt resistor and the current flowing through the voltage being dropped across the shunt resistor can be measured.

I have attached the wiring configuration for the battery baton binder connector ends for two different battery batons and also a circuit that I have thought of that may do the trick for now.

Any ideas?

I confess to have understood only part of your questions. Anyway I will tray to share my (small?) experiences.

• For the reverse protection my suggestion is to apply to the pins D and S of the device a simple resistor and a LED in the reverse polarity. It will light when the polarity is reverse.

• For the overcurrent or short circuit, if you don't need a very quick response, I want suggest you to use devices as Polyswitch. Applying in parallel to it the usual resistor and LED (in the direct way) you will see to light it when the current it's been behind the 'Trip current' for enough time to turn the Polyswitch in the open (not absolute) state.

I hope that this my answer will be useful to 'tune' me into your problem.

Assuming the unit-under-test is not powered:

For pin-to-pin short, you can apply a reference voltage to one pin and then measure the voltage on the other pin. If both pins have the same voltage, then they are short. If not, then they are open (or there is something in between).

For pin-to-ground short, you can apply a reference voltage to one pin, and then measure the voltage of that same pin.

If the UUT is powered, you might need to put a diode before the sources of PMOS to prevent reverse current.

Reference circuit below hasn't been tested.