Sunday, June 5, 2011

intercom using transistors

The circuit comprises a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pressed, the amplifier circuit formed around transistors T1 & T2 gets converted in to an asymmetrical astable multivib-rator generating ring signals. These ring signals are amplified by transistor T3 to drive the speaker of earpiece.
Current consumption of this intercom is ten to 15 mA only. Thus a 9-volt PP3 battery would have a long life, when used in this circuit.
For making a two-way intercom, identical units, as shown in figure, are necessary to be used. Output of amplifier unit goes to speaker of the other unit, & vice versa. For single-battery operation, join corresponding supply & ground terminals of both the units together.
The entire circuit, along with microphone & earpiece etc, can be housed inside the plastic body of a cell phone toy, which is basically obtainable in the market. Suggested cell phone cabinet is shown.

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