2 LED flasher with two 2N3904 transistors

Posted on Mar 20, 2013

This is a simple LED flasher using two 2N3904 transistors. Classic astable multivibrator using 2 transistors. Transistor is not critical. Try these: 2N4401, 2N2222, NTE123A, NTE123AP, NTE159, TUP/TUN and those in your junk box, you may find that most of them will work. Obviously, the 470 ohm resistor determines the LED's brightness and limits the current flow to about 20mA. 390 ohm can also be used as a save value. If you decide to go with a green or yellow led, which draw more current, you may want to replace the 470 ohm with 270 or 330 ohm values.

2 LED flasher with two 2N3904 transistors
Click here to download the full size of the above Circuit.

Flash rate is determined by the 39K resistors and the 10µF capacitors (determines the 'ON' time). The two sides do not have to match. Different values for each side can give a nice effect for unique duty-cycles. Flashrate for above circuit is 1 cycle per second.

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