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Project Notes

#183 Polarity Tester

Demonstrate a polarity-testing circuit using the CD4069 inverter.

The Build

Notes

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.

Construction

Breadboard

The Schematic

The Build

Credits and References

About LEAP

LEAP is my personal collection of electronics projects - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting.

Projects are often inspired by things found wild on the net, or ideas from the many great electronics podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know or send a pull-request.

NOTE: For a while I included various scale modelling projects here too, but I've now split them off into a new repository: check out LittleModelArt if you are looking for these projects.

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