Low Cost Transistorised Intercom

Several intercom circuits have appeared in www.circuit-lab.com using integrated circuits. The circuit described here uses three easily available transistors only. Even a beginner can easily assemble it on a piece of veroboard. The circuit comprises a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pressed, the amplifier circuit formed around transistors T1 and T2 gets converted into 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 10 to 15mA only. Thus a 9-volt PP3 battery would have a long life, when used in this circuit. For making a two-way intercom, two identical units, as shown in figure, are required to be used.

Output of one amplifier unit goes to speaker of the other unit, and vice versa. For single-battery operation, join corresponding supply and ground terminals of both the units together. The complete circuit, along with microphone and earpiece etc, can be housed inside the plastic body of a toy cellphone, which is easily available in the market. Suggested cellphone cabinet, with the position of switches, speakers and mike etc is shown.

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LM 390 based on 2 Way Intercom

This is a really easy 2-way intercom circuit primarily based on a LM390 audio amplifier circuit . the intercom circuit is a stand-alone electronic communications system intended for limited or private dialogue. For this circuit youll use a 8 ohms speaker, one for each station and require a vi volts dc power offer. Gain management will be done by capacitively coupling a resistor (or FET) from pin vi to ground.

The LM390 Power Audio Amplifier is optimized for 6V, 7.5V, 9V operation into low impedance loads. The gain is internally set at twenty to stay the external part count low, however the addition of an external resistor and capacitor between pins 2 and vi wil increase the gain to any value up to 200. The inputs are ground referenced while the output is automatically biased to at least one 0.5 the provision voltage.

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3M Wireless Intercom System

3M Wireless Intercom System circuit Diagram

The afterward schematic shows the 3M Wireless Intercom Arrangement Circuit and Components Diagram. The 3M Wireless Intercom Arrangement is advised for aerial reliability, compactness, and affluence of service. It is advised to accommodate two-way, radio-frequency audio advice in quick account drive-through restaurants and accessibility stores. The arrangement can be programmed to accomplish on any one of 16 altered channels to accommodate high-quality audio achievement and abate the achievability of arrest amid adjoining wireless systems.

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