Electronic circuits that use the 555 Timer

555 Timer Circuits

555 Timers are fun and a great way to start learning electronics

TRANSISTOR TESTER Circuit



The 555 operates at 2Hz. Output pin 3 drives the circuit with a positive then zero voltage. The other end of the circuit is connected to a voltage divider with the mid-point at approx 4.5v. This allows the red and green LEDs to alternately flash when no transistor is connected to the tester.

If a good transistor is connected, it will produce a short across the LED pair when the voltage is in one direction and only one LED will flash. If the transistor is open, both LED�s will flash and if the transistor is shorted, neither LED will flash.

Comment on this circuit or view the Electronic Circuits Community Forum.