Oct 31, 2008

door bell

This circuit consists of two 555 ICs. IC1 is used functions as monostable and IC2 is wired as astable multivibrator. The loud speaker LS1 sounds a bell tone as long as the time period of the monostable multivibrator (IC1).

             The circuit is powered by a 9v battery. When switch S1 is pressed, IC1 is triggered at its pin 2 and output pin 3 goes high for a time period set using preset VR1 and capacitor C1. The high output if IC1 resets Ic2 and it starts oscillating to produce a bell tone through the loudspeaker. The frequency of oscillation of IC2 can be varied with the help of preset VR2, so various tones can be heard through loudspeaker LS1.


Components required

              IC1- NE555

     IC2- NE555

LS1 (loudspeaker)-8Ώ, 1W



R1- 4.7K

R2- 10k



C2-0.01 μ

C3- 0.01 μ

C4- 0.01 μ

C5-100 μ, 25