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. 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, 2
N2222 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.