Electronic light flasher

  
The blinking or flashing rate is determined by Ul, a 555 timer integrated circuit. Its output, at pin 3, feeds U2, a HI1J triac driver. That driver consists of an infrared LED that is coupled internally to a light-activated silicon bilateral switch (DIAC). When the LED internal to U2 is turned on by the timer, Ul, its light triggers the DIAC; effectively closing the circuit between pins 4 and 6, and fires the Triac, TR1 through its gate circuit. When the Triac is firing, it acts as a closed circuit that turns on the light (or other device it may be controlling).
Electronic light flasher - schematic

When the timer turns off, the LED, the DIAC and Triac stop conducting and the light turns off. The sequence then repeats. The flashing rate can be varied by means of Rl, a 500,000 ohm potentiometer.




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