The IC LS1240A from SGS Thompson is specifically designed for generating a 2 tone ringtone generator circuit. Thus the IC specifically becomes suitable for landline telephones for producing the ringtones when a call is received.

However with little modifications the IC can be easily utilized for normal applications, in circuits where a double tone alarm may be required.

Technical Specifications

Basically the IC is a 8-pin DIL chip resembling the IC 555 and has the following specs:

  • Very low current consumption yet good audible response at the output.

  • Internal built-in rectifier stage for rectifying an AC input supply, a filter capacitor is also a built-in feature of the IC.

  • Hardly any external components required for setting up the circuit.

  • The tone of the output musical audio can be adjusted externally through a resistor.

  • If the IC os used inside a landline telephone then the supply to the IC is derived from the line voltage via a 1uF capacitor.

  • The IC is able to drive a piezo electric transducer directly without the need of inductors or amplifiers.

  • The IC is also capable of driving a small loudspeaker directly for generating the musical output.

  • However the speaker must be rated at minimum of 50 Ohms.

  • The following 2 tone ringtone generator circuit shows how to configure the IC LS1240 as a two tone musical signal generator circuit.

Pinout Details of the IC LS1240 dual tone generator IC

Pinout S[ecs of the IC LS1240 dual tone generator IC


Circuit Diagram of two tone music generator using IC LS1240


Two Tone Generator using piezo element



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