Here is a ‘beeper’ circuit employing two timer ICs NE555 (IC1 and IC2). The beeper circuit using timer IC NE555 can be used in various circuits that require an alarm or a ‘beeping’ signal.
Description of Beeper Circuit Using Timer IC NE555
Timer IC1 is used here in astable mode in such a way that square-wave output at about 1 Hz is obtained. IC2 is also configure in astable mode, but it gives an output with about 1 kHz frequency.
The output if IC1 (pin 3) is connected to ‘Reset’ terminal (pin 4) of IC2. So, this continuous 1 kHz tone of IC2 is interrupted by the 1 Hz signal from IC1, producing a ‘beeping’ sound. Capacitor C4 is used to restrict DC signals.
The beeper circuit operates satisfactorily when it is to be activated by a relay or a mechanical switch, but when it is to be operated by logic ICs, such as CMOS or TTL ICs, a bit of modification is required. Instead of connecting pin 4 of IC1 to Vcc, it should be connected to the output of the logic element through which it is to be activated. A logic ‘1’ at pin 4 will activate the beeper and logic ‘0’ will turn it off. Rest of the circuit would remain the same.
PARTS LIST OF BEEPER CIRCUIT USING TIMER IC NE555
Resistor (all ¼-watt, ± 5% Carbon)
R1, R3 = 1 KΩ
R2 = 680 KΩ
R4 = 10 KΩ
|C1 = 1 µF/25VC2, C3 = 0.01 µF|
C4 = 33 µF/25V
C5 = 100 µF/25V
C6 = 0.047 µF
|IC1, IC1 = NE555|
|LS1 = 8 Ω, loudspeaker|