This is a wonderful project of electronic world. The main attraction of this project is that when this project is fixed in parallel to the telephone line gives you the information by putting on the light in addition to the ringing of the bell by the telephone. It makes easier for children and old people to attend the telephone call. In the darkness of night when a bulb gets lighted there is no difficulty in locating the telephone.
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.
The working system of this project mainly depends upon IC 555 and ringing tone of the telephone. When telephone rings it gives a 50Hz AC tone which is connected to the base of transister BC148 through a 0.1mfd condenser. Thus necessary voltage are obtained at the base of transister BC148. The output of the transister is connected to the pin no. 2 of the IC555. In this project IC555 has been used as a timer. This triggers the IC555. The output of the IC555 is available on the pin no. 3 and this output is connected to the base of another transister BC148. By driving this transister the relay connected to the collector of this transister operates. The load which can be a bulb / bell is connected with its contacts. The time period to operates this relay on IC555 is controlled by a 1M volume control. With the help of reset switch this project can be reset. You can close the timer before its fixed interval by resetting it.
PRECAUTIONS WHILE ASSEMBLING THE PROJECT:-
* Do not allow main AC 220V to touch the telephone lines.
* Do not solder IC directly on PCB because leakage of current through the soldering iron there is possibility of parts getting spoiled.
* Take special care while soldering transister about its base, emitter and collector.
* Take care of about the polarity of the diodes while soldering it.
* Do not touch the transister while checking it with the multimeter.
PCB [CODE 6TP11]=1
1K=1, 10K=2, 4K7=2, 1M [Pot] =1
0.1/400V =1, 0.01/50V=1
PUSH TO ON SWITCH =1
RELAY [12V]=1 Pcs
One ON Telephone Connection =1
One Electric Bulb [ 60 Watt] =1