The figure below shows a very useful project of a telephone ring tone generator circuit. The circuit can be used for many purposes like intercom bell, calling bell etc. It is built around two 555 timer ICs. Both the ICs are connected as astable multivibrator in the circuit. The output of IC1 is fed to
the pin5 of the IC2 through a 10K variable resistor due to which the output frequency of IC2 is being controlled by IC1.The project is also using two variable resistors, which are 10K and 100K to adjust the output sound.
An 8 ohms 0.5W to 1W speaker is used in the circuit that is directly connected with the output of the IC2 through a 10uF electrolytic capacitor. The circuit will provide quite loud sound when it will be operated with 9 to 12V DC. For further increasing the sound you can also use a one transistor amplifier at the output of the IC2.
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