Simple Polarity Tester

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1K 1/4W Resistor D1 1 Green LED D2 1 Red LED D4, D5, D6, D7 4 1N4001 Silicon Diode 1N4004, 1N4005, 1N4007 MISC 1 Board, 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.