Alternating ON-OFF Control

Parts List
Resistors are carbon, 1/2 Watt, 5% tolerance.

R1 = 10K
R2 = 100K
R3 = 10K
C1 = 0.1F, Ceramic (100nF)
C2 = 1F/16V, Electrolytic
D1 = 1N4001
Q1 = 2N4401 (ECG123AP, NTE123AP, etc.)
IC1 = 4069, CMOS, Hex Inverter (MC14069UB), or equivalent
S1 = Momentary on-switch

  • Use this circuit instead of a standard on-off switch. Switching is very gentle. Connect unused input pins to an appropriate logic level. Unused output pins *MUST* be left open!

  • First 'push' switches ON, another 'push' switches OFF.

  • You can use 1/4 watt resistors if they are metal-film type. For the regular carbon resistors use 1/2 watt (depending on application).

  • Any proper replacement for Q1 will work, including the european TUN's. However, if you use the NTE or ECG replacement parts, take note of the 'AP' types. The regular 'A' type will NOT work and is NOT the same. (e.i. NTE123AP is not the same as NTE123A).

  • For C2, if you find the relay acts not fast enough, leave it out or change to a ceramic cap between 1 and 10nF. It is there as a spark-arrestor. If you find that the relay is 'sticking', that is also caused by the 1F capacitor. Try to leave it out, you may in fact not need it at all.

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    Copyright 1995 -- Tony van Roon