2) LED as a Continuity tester: The above shown circuit is LED as continuity tester. This circuit is used for checking continuity of cables, connectors and switches. When A and B terminals are shorted, ...

The red led will drop about 1.8V, the green about 2.2V, both should be operated at abuot 20mA.<BR>With the 100 Ohm resistors you're using, the red led will draw over 70mA when on, the green almost ...

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 ...

October 9, 2013 [Henryk] just sent us his latest episode of simple LED circuit puzzles. In front of the camera he solders one pin of each of the 3 LEDs to a different switch.

With the circuit values shown, R2 will drop a bit less than 5 V before D3 turns on. Prior to turn on, D2 remains back-biased and no current flows through the LED (D1).

We'll start with the simplest from a circuit point of view. Suppose you plan to put all the LEDs in one series string and the voltage required to drive the string exceeds 60 V.