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Simple Polarity Tester

By Dudley LeRoux

This tester can be used to check the polarity of any power source, and is therefore very useful when installing automotive equipment, alarm systems or anything else you can think of. Because this circuit is so simple and cheap, even frying one with an over voltage is not a big deal.

Schematic


Schematic for polarity tester

Parts:


Part
Total Qty.
Description
Substitutions
R111K 1/4W Resistor
D11Green LED
D21Red LED
D4, D5, D6, D741N4001 Silicon Diode1N4004, 1N4005, 1N4007
MISC1Board, Wire, Case, Probes

Notes:

1. Email Dudley LeRoux with questions, comments, etc.

2. To use the circuit, just connect your probes to the source under test. If D1 lights up, the left most probe (on the schematic) is connected to positive. The opposite is true if the left probe is negative. If both LEDs are on, the source being probed is AC.

3. Be careful when using this tester not to probe a source greater than about 12V.

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