FLASHER CONTROL

EXTERNALLY CONTROLLED FLASHER

This extremely simple circuit is built around two npn transistors BC547.  R C network R3 and C2 decides the flash rate of LED.  When high logic is given to the open end of resistor R1 (10K) transistor Q1 immediately starts conducting and LED glows.  Capacitor C2 gets charging through resistor R3.  As soon as the voltage at the base of transistor Q2 via resistor R2 reaches above the voltage at the emitter of Q2+0.6 V transistor Q2 starts conducting.  The voltage at base of transistor Q1 immediately pulled down to ground level resulting in switch off the LED and capacitor C2 gets discharged through R3, R4 and R5.  Thus the cycle repeats till the logic at the open end of R1 is removed.  R4 is current limiting resistor for LED.