Long duration timer relay, 1 min to 20 hrs

Parts List:
   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