PN Junction tester

This transistor tester tests bipolar junction transistors junctions. It tests the junctions for open and short circuits. It uses 4 resistors, 4 LEDs and 1 SPDT switch. A good transistor will only have 2 out of 4 LEDs lit, on one side of the switch and 4 on the other. You can also test standard diodes (rectifiers and switching diodes). A diode will have 3 out of 4 LEDs lit on one side and 4 on the other.

Here’s a table of all possible readings and their meanings

2 LED lit	Both emitter/collectors are short circuited
3 LEDs lit	Only one emitter/collector
4 LEDs lit	Open circuit
1 LED lit	Circuit design error