Telephone

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The circuit is turned off when the phone line is 45v as the voltage divider made up of the 470k, 1M and 100k puts 3.5v on the base of the first BC557 ...

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Two circuits are available to show when a phone is being used. The first circuit must be placed between the socket on the wall and the phone - such as...

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This circuit consists of a 4-transistor amplifier and a 3-transistor "switch" that detects when the phone line is in use, and turns on the amplifier. ...

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The circuit will transmit a phone conversation to an FM radio on the 88-108MHz band. It uses energy from the phone line to transmit about 100metres. I...

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The circuit will transmit a phone conversation to an FM radio on the 88- 108MHz band. It uses energy from the phone line to transmit about 200metres. ...

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This circuit has poor features but you can try it and see how it performs. It uses a PNP transistor and requires a separate antenna. It also has a sup...

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This amplifier circuit is used in all home telephones to amplify the signal from the line to the earpiece. The voltage is taken from the line via a br...

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