I remember that this was my first circuit several years ago when I used to go to an Electronic Club in my home town.
Few days ago I wanted to do something simple (I do this kind of stuff as relaxation, in the day-by-day life I work as a programmer) with LEDs so this was the right choice :).
So here is the circuit :
and the components for it :
- T1, T2 : 2N3904 or almost any NPN transistors (BC171 , BC172 , 2N2222 etc)
- C1, C2 : 10uF / 16V
- D1, D2 : LEDs
- R1, R4 : 470 Ohms @ 0.25W
- R2, R3 : 39 KOhms @ 0.25W
The circuit is extremly simple to build :D, the LEDs flashes around once/second. If you want to increase/decrease the flashing rate modify the values of the R2, R3 resistors. The formula for it is about 3*R(in KOhms)*C(in uF)/1000 seconds so, as an example, for this specific circuit :
Here are some pics I made during the building :
Here is a sample video of how it works: