Timer circuit

Posted on Dec 23, 2012

A wide rage auto turn OFF timer covering 1 minute to 20 hours in three ranges with S1. As soon as power is applied to the circuit the IC1 [555] starts to oscillate happily and feeds clock pulses to the IC2 [4017]. The IC2 [4017] and IC3 [4020] give a combined count rate of 81920 before the output of the IC3 [4020] goes high and turns Q1 on. With pot RV1 adjust the Time.

Timer circuit
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Part List R1=2.2Kohm C1=120nF 63V polyester IC2=4017B R2=39Kohm C2=1.2uF 63V polyester IC3=4020B R3=1Mohm C3=100nF 63V Q1=BC214 R4=27Kohm RV1=470Kohm pot. S1=2X3 SEL SWITCH R5=12Kohm D1-2=1N4001 S2=Push button no R6=6.8Kohm IC1=LM555 RL1=12V >120ohm Relay

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