LONG DURATION TRANSISTORISED TIMER
The special features of this project is that, its duration can be adjusted for a long interval and it does not employ any IC. With the help of this project, you can ON/OFF any gadget for a long duration.
TECHNICAL DESCRIPTION AND WORKING
This project has been developed and tested O.K. in our TV Engineers Technical Lab. The components and PCB used in the projects published in our books are available for sale at resonable price.
In this project two transistors (BC148 and BC158) are employed. The ON/OFF time can be adjusted through the preset. Its working depends on the transistor biasing for conduction. The capacitor connected to the transistor BC148 is the discharge capacitor. The value of capacitor can be increased or decreased and corresponding ON/OFF time can be obtained. When the Push to OFF switch is pressed, the transistor BC158 triggers and relay becomes OFF.
PRECAUTIONS WHILE ASSEMBLING THE PROJECT:-
*Check polarity of electrolytic capacitor while mounting on PCB otherwise reverse connection may damage it.
*Pay attention to the wiring and loose connection in project while assembling.
*Check Dry soldering & short circuit in the board after soldering.
*First of all check all the components as per circuit.
*Please use resistance of the exact value as given in the circuit.
*While mounting transistor, you should connect collector , base & emitter properly.
*Check polarity of diodes [anode and cathode]
TRANSISTOR BC158 = 1
BC148 = 1
RELAY 12V = 1
DIODE IN4007 = 1
2200MFD/25V = 1
820E = 1
10K = 1
3K3 = 1
5MEG = 1
4K7 = 1
PUSH TO OFF SWITCH = 1