Delayed pulse generator

  
The circuit offers independent control of initial delay and pulse rate. ICIc is connected as a pulse generator whose operation is inhibited by the normally low O/P of the ICla. When the circuit input goes low i.e., by pressing PB1, IClb O/P goes high and the circuit O/P goes low thus replicating the input. When the input is kept low capacitor Cl charges via R2 to a point where ICla O/P goes low. This allows the pulse generator ICIc to start and `rapid fire` pulses appear at the circuit O/P. When the circuit input returns to the high state Cl is rapidly discharged viaD1 and Rl.

The value of R2 and Cl control the initial delay while R3 and C2 control the pulse rate. The values given will give a delay of around 0.5 seconds and a pulse rate of 200/300 Hz depending on supply voltage. PB1 may be replaced by an open collector TTL gate or a common emitter transistor stage if required.




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