demonstrate a polarity-testing circuit
A simple polarity testing circuit uses a series of inverters. The input signal is pumped into two parallel chains:
- a single inverter
- a series of two inverters
So, regardless of input polarity, one chain output will be high and the other low.
| input | Single-inverter Output | Dual-inverter Output |
|---|---|---|
| LOW | HIGH | LOW |
| HIGH | LOW | HIGH |
The signals are tied together with two reverse-polarity LEDs in series. So one will always be alight when the other is not. The unlit LED is subject to a reverse voltage equivalent to the forward voltage of the other LED. Most LEDs will handle this without complaint.
