Eprom-Controlled Time Switch

60 EE March 1989 EPROM-CONTROLLED TIME SWITCH by J. Vinckier Time switches can take many shapes. Where apparatus has to be switched on and off at regular intervals, a simple electronic switch will suffice. This article describes such a device that is controlled by a suitably programmed EPROM. It has battery back-up to ensure continued operation in the case of mains failure. The circuit consists essentially of three parts: a crystal-controlled time base, IC1 and IC2; an address counter, IC4; and an EPROM, IC3. The time basis is controlled by a 32.768 MHz crystal, XI, which is of a type frequently used in quartz watches and clocks. The 14-stage counter on board IC1 divides the oscillator signal to 2 Hz. That signal is fed to a second counter, IC2, whose Q6 output is con- nected to address counter IC4. The fre- quency of the signal at Q6 is 1/64 Hz: the address counter therefore receives a pulse every 64 seconds, upon which it in- creases its content by 1. The Q0-Q10 outputs of the...