This is a very simple project using a printed circuit board and 8 components. It will flash an ordinary 3mm or 5mm (1/8` or 1/4`) LED at a rate of about one flash per second. This circuit works on the basis of a high-gain amplifier being driven into saturation (fully turned-on), firstly by the very small amount of current delivered by a high-value resistor and then from energy stored in an electrolytic.
When the supply is connected, both transistors are off and the electrolytic charges via the 330k resistor and 22R. When the voltage on the base of Q1 rises to about .6v, the transistor begins to turn on and the resistance between its collector-emitter ter