Telephone monitor

It is sometimes necessary to make a telephone conversation audible to more than one person at either end or to make a tape recording of it (as in many businesses). Often, this is done with the aid of a microphone fitted with a suction cup. This does not work very well, though, hence the present circuit.[…]

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Privacy phone

Undesired listening-in to phone conversations may be prevented by the present circuit, which requires only two components to protect a telephone. In each telephone to be protected, a traic is in each telephone to be protected, a triac is inserted in series with the line. A diac is connected between the anode and the gate[…]

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House telephone

Telephones are now readily and cheaply available: two identical ones and a handful of components enable a simple house telephone to be set up. Since the two telephones are connected in series as shown in the diagram, half the supply voltage exists across either of them. Neither buzzer will sound since the potential across zener[…]

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Binary logarithmic ladder network

Binary logarithmic ladder network: The network provides an attenuation between 0 dB and 78.75 dB that is presettable in 64 steps with the aid of a 6-bit code. Six independent, relay switched attenuator sections may be connected in series in accordance with the input code. Since the sections have identical 1 kΩ impedances, they do[…]

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Solid State

Solid State Voice Recorder

Integrated circuits ISD 1012, ISD 1016 and ISD 1020 from chip maker ISD enable sounds to be recorded and played back. The final two digits in type coding show the length of a sound message in seconds. The difference in recording and playback is caused by the sampling frequency. which is highest (10.6 kHz) for[…]

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