Schematic Diagram

Flashers are useful as visual metronomes, and for decoration and advertising purposes, here we learn how to build one at home. Conventional. thermal flashers make use of a bimetallic strip which alternately heats and cools, thereby breaking and making an electrical contact. Such flashers are uureliabledue to various mechanical problems. glimther, due to sparking at the contacts, their life is limited, and also their flashing rate is not constant. The solidstate electronic flasher described here suffers frdm none of the above disadvantages. A 555 timer IC operated as an astable multivibrator is used to control the on and off times of triac, which in tum controls power to the lamps. The flashing rate is determined by settings on the potentiometer, and is approximately given by  

f = 43/(VR1+R2)C flashes/minute

Hence by varying the resistance included through 250K potentiometer (VR1), it is possible to adjust the flashing rate   from about 6 flashes/ minute (slow) to about 60 flashes/ · minute (fast). The on and off times are almost equal due to symmetry of the astable circuit.  The ST44A triac used here has a 400 PlV, 4-amp rating; With it the load must be restricted to a maximum of 500W. The triac should be clipped to at suitable electrically isolated heatsink. The unit should be assemble inside a plastic or wooden box, and on switching it on, no part of the circuitry, except the rate adjust potentiometer (which must preferably have a plastic knob) should be touched as all parts will be alive. An approximate cost of the electronic ponents used is Rs 100/-