R1 = 2K2 IC1 = 555, timer
R2 = 39K IC2 = 14017, decade counter
R3 = 470K (pot) IC3 = 14020, divider
R4 = 1M Q1 = 2N3906
R5 = 27K D1 = 1N4001
R6 = 6K8 D2 = 1N4001
C1 = 0.12uF, ceramic S1 = Push switch, momentary on
C2 = 1.2uF, polyester S2 = 3-step/2-deck rotary switch
C3 = 0.1uF, ceramic Ry1 = 12V
Fig. 11: Shows a 'long-range timer relay' switching circuit which spans
1 minute to 20 hours in three ranges using a three-step, two-deck mechanical rotary switch.
IC2 (4017) is a CMOS decade counter IC, a five-stage Johnson counter with 10 decoded outputs. Inputs include a CLOCK,
a RESET, and a CLOCK INHIBIT signal. This IC, together with IC3 and the 3-step rotary switch, can provide a maximum
division ratio of 81,920 making it possible to time for periods up to 20 hours or so. Circuits like this are used in
battery chargers and area security lighting systems with time-controlled turn-off.
IC3 (4020) is a CMOS 14-stage, ripple-carry binary divider. Normally a 'high' would occur as soon as switch S1 is
closed and a 'low' when the 8192nd astable pulse arrives. All counter stages of IC3, the 4020, are master-slave
flip-flops. The state of a counter advances one count on the negative going transition of each input pulse, and a
high level on the RESET line resets the counter to its all zeros state. All inputs and outputs are buffered.
Copyright © 2003 - Tony van Roon
ALL RIGHTS RESERVED