Here is the circuit diagram of multitone alarm. This is a low cost circuit which is simple and easy to build. The main components of this circuit is based on dual op-amp MC1458 and LM 380. The two op amps inside the MC 1458 are used to produce square and triangular waves. LM 380 is used to amplify the output. The first op amp IC1a is wired as an astable multi vibrator and second op amp IC1b is wired as an integrator, to make the square wave triangle.
The two output square ans sine can be selected using switch S1 to the input of IC2 which amplifies it to drive the speaker. POT R4 can be used for tone adjustment.
- IC1a and IC1b are same. So their power supply is common. Pin 6 of IC2 (inv input) has no connection.
- C1 and C2 are ceramic, C3 is electrolytic capacitor.
- A dual polarity power supply is needed here. Just need center tap transformer, bridge diode and an electrolytic capacitor. You may search the circuit in this site.