Alternating Blinker

The circuit represents a general-purpose astable multivibrator that alternatively energises two heavy loads via a relay (in this case, the loads are 12-V incandescent lamps). In contrast to an ‘analogue’ flip-flop, here it is not necessary to use power transistors with heatsinks. This alternating blinker can thus be built at a lower cost, more easily and more compactly.In the idle state, capacitor C1 is charged via R1 and at the same time discharged via R2 and P1. Here P1 must be adjusted such that sufficient current is available to switch on transistor T1. This should occur when the voltage on the capacitor is around 1.2 V, if a BC517 is used. As a consequence, the relay pulls in.