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Friday, 3 October 2014

simple project Programmable Timer

Easily Make A Simple Programmable Timer

This is one of the simple circuits programmable timer in the series of timer. The time range of this programmable timer is of few second to 90 minutes can be selected by single circuit.
Circuit Description of programmable timer

The whole circuit of programmable timer is build from two ICs i.e. IC 555 (IC1) and IC 7442 (IC2). IC1 is used in monostable mode where output is low when trigger pin 2 is high and vice-versa. The output is high only for preset time determined by the value of capacitor C1 with its corresponding preset with the help of switch SW5.

IC2 is used for selecting the required time duration. The 10 different outputs from programmable timer are connected to its corresponding 3 Volts relay where preset VR1 through VR10 is connected to RL1 through RL10 respectively. Table in below shows the appropriate binary codes.

NOTE: If the relay does not work then a relay driver circuit may be used to operate.
Resistors (all ¼-watt, ± 5% Carbon)

R1, R2, R3, R4, R6, R7 = 10 KΩ

R5 = 1 KΩ

R8 = 220 Ω

R9 = 520 Ω

VR1 = VR10 = 2.2 MΩ

C1 = 2200 µF/25V

C2 = 0.01 µF

IC1 = NE555 (Timer IC)

IC2 = 7442

T1 = BC108

D1 – D20 = 1N4007

TR1 = ST44

SW1 – SW4 = ON/OFF switch

S5 = push to on switch

RL1 – RL10 = 3V, 100 Ω relay

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