Time-delay relay & proximity control

Posted on Aug 12, 2012

The design uses a proximity detector rather than a pushbutton switch to eliminate the need to mount and wire any equipment outdoors. The circuit worked well in this application and other applications.

The heart of the circuit is the quad CMOS NAND gate, IC1. A human hand near the sensor induces 60-Hz power-line noise into IC1A, and this IC triggers IC2. IC2 is configured as a monostable multivibrator, with a period equal to 1·1(R3+R4)(C3). The perio

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