This tutorial will give you an introduction to basic electronics for beginners. Learn about electronic elements and electrical study

Tuesday, August 01, 2017

Several timer circuit have been published in www.electronicsproject.org, but this is a unique timer circuit with no timer IC in use. It is transistorized timer having a 2-stage audio amplifier and a relay driving unit.

The incoming sound waves are transformed into a low audio signal by the condenser (mic). The direct coupled audio amplifier built around transistors T4 and T5 amplifier the tiny signal. The amplified signal is rectified by Diode D1 and is fed to the base of T3. Capacitor C1 starts charging through T3. The charge of C1 switches on transistors T2 and T1 simultaneously. T1 energizes the relay and the load gets power through it.

The time period is maintained by C1, whose value can be in between 10 ÂµF to 220 ÂµF. It is found that the delay time is about one sound with 10 ÂµF capacitors and it is about 20 seconds with 220 ÂµF capacitor.

The circuit easily be mounted on a small veroboard. You can control radio, TV, taperecorder or any other electronic equipment with this timer.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)
R1 = 2.7 Kâ„¦
R2 = 100 â„¦
R3, R10 = 100 Kâ„¦
R4 = 220 Kâ„¦
R5 = 27 Kâ„¦
R6 = 3.3 Kâ„¦
R7 = 1 Kâ„¦
R8, R11 = 10 Kâ„¦
R9 = 270 Kâ„¦

Capacitors

C1 = 10 ÂµF/12V
C2 = 0.04 ÂµF
C3 = 0.1 ÂµF

Semiconductors

T1 = AC128 or AC188
T2 – T5 = BC148
D1 = 1N4001

Miscellaneous

MIC1 = Condencer Mike
RL1 = 6V 100â„¦ relay
Several timer circuit have been published in www.electronicsproject.org, but this is a unique timer circuit with no timer IC in use. It is transistorized timer having a 2-stage audio amplifier and a relay driving unit.