In the diagram as you can see two LED’s are placed in opposite directions so when one LED is ON the other LED will be OFF. I have used Red and Green LED’s. When node A is positive green LED glows ...

It may also be used to check a string of LEDs (one at a time) to make sure that all are installed correctly. LED Tester Circuit Schematic simple led tester schematic Why 3V? 3V is sufficient to turn ...

An LED tester can be as easy as a constant-current power supply, and in fact that’s what [Dave]’s first LED tester was, in essence. Set an LM317 circuit up to output 10mA, say, and you can ...