Figure shows the circuit diagram of multi tone alarm. This is basically an amplifier circuit. The central part of this circuit is the dual operational amplifier IC MC 1458 and the operational amplifier LM 380. The IC MC 1458 consists of two operational amplifiers which are used in this circuit as square and triangular wave generators. The operational amplifier LM 380 is used as the output power amplifier.
Out of the two operational amplifiers in MC 1458, one is connected as astable multivibrator to generate square wave and the other is connected as integrator to generate triangular wave from square wave. One of the two outputs among square and triangular is selected using a switch S1 before giving it into the final amplification stage. The final amplified output is used to drive the speaker. A dual DC power supply of is used here for powering the circuit.
- Use a good quality PCB to assemble this circuit.
- This circuit can be used in burglar alarms or sirens.
- POT R4 is used for tone adjustment.
- The inverting input (pin 6) of IC LM 380 has no connection.