Chime circuit are most popular among clock and other indicating applications. Usually chime is constructed using timer or other oscillators. The circuit described here uses inverter (NOT Gate) with resistor and capacitor to produce oscillation as well as for producing decay. The main advantage of this circuit is low cost and low power consumption.

Circuit description

Resistor R1, capacitor C1, and two inverters form a square wave generator, which produces the basic tone. The generator is followed by an inverter that acts as both a buffer and a driver for the speaker. Resistor R2, which has a minimum value of 100 ohms, limits the current and controls the volume. Diode D1, capacitor C2, resistor R3 and R4 and two inverters create the pulse generator that determines the turn on and decay time of the chime. The delay circuit formed by D2, C3, R5 and transistor Q reduces the amplitude of the chime time exponentially as a function of time.

Note that any NOT gate IC can be used with the circuit.

   Schematic

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