Design Ideas: January 5, 1995
The unpretentious controller in Fig 1 remembers the interval between your pressing its start and stop buttons. Thereafter, the controller switches the load on and off every day at the same times as you did. You reset the controller by pressing the buttons to enter settings.
An inexpensive digital-watch crystal, oscillating at 32.769 kHz, and IC1, a CD4060B oscillator and 14-stage counter, derive a 2-Hz clock. IC2 further divides this 2-Hz clock by 120 to generate a clock having a 1-minute period. IC4 and IC5 are "day" clocks. They count the 1-minute clock, resetting themselves every time their count reaches 1440 (1440 minutes=1 day). (The diodes at the outputs of counters IC4 and IC5 constitute an AND gate.)
Pressing the start button sets both flip-flops in IC3 , switching on the load. IC3A also resets counter IC4 to zero via the 10-nF capacitor. Later, pressing the stop button resets IC3 's flip-flops and resets counter IC5 . IC4 and IC5 still reset themselves once per day. But now you have synchronized each counter to your latest button pressings. The 9V battery backs up the circuit. (DI #1603)