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Tone dial encoder – Circuit Schematic
Tone dial encoder
Tone dial encoder with automatic PIT control...
Telephone line monitor – Circuit Schematic
Telephone line monitor
Using rectified audio as a power supply...
Telephone or extension tone ringer – Circuit Schematic
Telephone or extension tone ringer
This circuit uses ML8204/ML8205 devices...
Telephone tone ringer – Circuit Schematic
Telephone tone ringer
This is a complete telephone bell replacement circuit with minimum external components with on-chip diode bridge and transient protection...
Telephone status monitor – Circuit Schematic
Telephone status monitor
The LED indicates the status of a remote telephone. The light is off if the phone is hung up. It shines steadily if the phone is off hook, and it flashes on and...
TV modulator using a motorola MC1374 – Circuit Schematic
TV modulator using a motorola MC1374
This one-chip modulator requires some outboard circuitry...
Telemetry demodulator – Circuit Schematic
Telemetry demodulator
The circuit recovers an FM audio signal that variesfrom less than 1 kHz...
Programmable multi-tone telephone ringer – Circuit Schematic
Programmable multi-tone telephone ringer
Two BST72 transistors provide an output voltage swing almost equal to the voltage at C3. ...
Speech with XR-T5995 – Circuit Schematic
Speech with XR-T5995
The XR-T5995 Speech Network is a monolithic integrated circuit specifically designed for implementing a low cost telephone circuit. ...
Tone ringer II – Circuit Schematic
Tone ringer II
The XR-T8205 Tone Ringer is primarily intended as a replacement for the mechanical telephone bell. The device can be.powered directly from telephone ac ringing ...
Telephone in-use indicator – Circuit Schematic
Telephone in-use indicator
This circuit functions as a line-current sensor and can be connected in series with either of the phone lines. For the circuit to indicate an "in use" status fo...
Telephone hold button – Circuit Schematic
Telephone hold button
The on-hook (no load) voltage across the red-green wires will be 48 V or slightly less when all telephones are on-hook (disconnected). When any telephone goes o...
Plug-in remote telephone ringer – Circuit Schematic
Plug-in remote telephone ringer
This device consists of a ring detector connected to the telephone line. When the telephone rings, the ring detector impresses high-frequency pulses on the ac p...
Remote telephone monitor – Circuit Schematic
Remote telephone monitor
This device monitors sounds in home or office when a telephone is called from a remote location. ...
High isolation telephone ringer – Circuit Schematic
High isolation telephone ringer
The diode rectifies the ringing signal to supply the operating power to the audio relaxation oscillator made up of LI, L2, Rl, R2, and C. Moreover, L2 together ...
Music on hold – Circuit Schematic
Music on hold
With this music-on-hold device, you can answer the phone in one room, place the caller on hold, and then pick up the phone again at another location. ...
Telephone ringing detector – Circuit Schematic
Telephone ringing detector
With the 555 timer connected as a multivibrator and an opto-isolator, ...
Automatic telephone recording circuit – Circuit Schematic
Automatic telephone recording circuit
The device is a dc switch that is normally on via the forward biasing of Ql via R3. Ql now clamps Q2 into a forward state by biasing its complement well into a ...
Musical telephone ringer – Circuit Schematic
Musical telephone ringer
The heart of the circuit is IC1, General Instrument's AY-3-1350 melody-synthesizer IC. IC2 is a TCM1512 telephone ring detector IC that is powered by the teleph...
Speech activity detector for telephone lines – Circuit Schematic
Speech activity detector for telephone lines
The circuit can be used in telephone lines for speech activity detection purposes. This detection is very useful in the case of half-duplex conversation between...