One-shot multivabrator timer relay

One shot multivabrator timer relay

Parts List:R1 = 1MD1,D2 = 1N4001, G.P DiodeR2 = 100K Q1 = 2N3904, NPN transistorR3 = 680KIC1 = 4001, CMOS ICR4 = 5K6 Ry1 = Relay, 12VC1 = 0.1uFS1 = Momentary push="on" switchC2 = 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.

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