One-shot multivabrator timer relay

Parts List:
R1 = 1M          D1,D2 = 1N4001, G.P Diode
R2 = 100K           Q1 = 2N3904, NPN transistor
R3 = 680K          IC1 = 4001, CMOS IC
R4 = 5K6           Ry1 = Relay, 12V
C1 = 0.1uF          S1 = Momentary Push="on" switch
C2 = see text
Fig. 10: This circuit shows a pair of CMOS NOR gates which form a push-button-activated one-shot multivibrator relay-switching circuit that provides delays up to several minutes with resonable accuracy. The relay turns on as soon as the START switch S1 is closed.
However, it turns off again after a preset delay of about 0.5 seconds per microFarad (uF) of the value of capacitor C2. The two CMOS gates are configured as a manually-triggered monostable multivibrator whose output is fed to the relay through R4 and transistor Q1.

Copyright © 2003 - Tony van Roon