Circuit knowledge

Many of my friends asked me for automatic on off led circuit or  led flashing circuit so here I’m going to post a Astable multivibrator-2 LED flashing circuit.

Circuit diagram of Astable multivibrator with 2 LED:

Fig:  Astable multivibrator-2 LED flashing circuit Circuit diagram

It is a simple astable multivibrator circuit using 2LED (here i used red LED), two NPN small transistor 2N3904 for switching. Here other small NPN transistor can be used, including  2N4401, 2N2222 or PN2222. Supply voltage is +3.7V to +5V or if you want to supply a larger volt then add a required resistor series connected with  2 LED’s. I recommend to use +3.7V for best result . for +3.7V you can use a battery of  mobile phone.


Pin diagram of transistor 2N3904:

Fig: 2N3904 Pin Diagram