This circuit is used to record telephone conversations on your landline telephone. All you will need is this small circuit and subscription of your PC. There are few times when we forget what we said or told us. So we need recording. Sometime, not many years....

DC voltage present on the telephone line is usually about 45 to 50V, on-hook and off-hook to 6V. The step-down circuit relay is activated. Relay control tape recorder. Audio is..

Diodes VD8 ~ VDI1, SCR vs composition control switch main circuit isolation diode VD7, stable orbital tube VD6, simple resistor capacitor C4 constitute buck regulator circuit, ..

Electronic lock using the telephone key (resistor connected plug) is inserted after the oscillator circuit start-up circuit, and the oscillation frequency is accurate or not to..

Use of ordinary telephone ringing circuit KA2401 and peripheral components, the installation of the light control when the bell..

Optically isolated phone automatic recording interface circuit, IC3 voice module...

The telephone-line tester consists of nothing more than a meter (that`s used to measure line voltage in the on- and off-hook state), three resistors (one of which is variable), a pushbutton switch, and a modular telephone connector...

The circuit has been designed to accommodate all those who dedicate many hours of their lives by exploring the endless pages of this site. Despite the fact that it consists of only three components (Most were not little!), Is able to provide an indication of....

IC-1 and the associated circuitry form a stable audio tone generator that feeds a buffer amplifier, Ql and Q2. The tone output is taken from the emitters of the transistor pair to supply a carrier voltage for a balanced modulator made up of four diodes—Dl....

This circuit consists of two audio channels, a control circuit, and a hybrid irlterface circuit. The gain of each audio channel is con· trolled by the control circuitry, with the use of a voltage controlled amplifier (VCA). The inputs to the control....

Audio from the telephone is inductively coupled to the base of Ql. which is used as a preamp. The preamp provides a gain of about 75 dB, to boost the input signal from .about 4 mV to about 300 mV pk-pk. If you use a higher gain transistor, increase the....

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 for all phones on a single line, it must be connected in series with the phone line before, or ahead....

The XR-T5995 Speech Network is a monolithic integrated circuit specifically designed for implementing a low cost telephone circuit. ..

This circuit converts a tape recorder into a completely automatic telephone conversation recording instrument that needs no external power source. Voltage at the switch terminals of tape recorder applied to a pair of Darlington-connected transistors, Ql and....

The cireiilt is built around a couple of low-cost ICs: an H11C4 optoisolator/coupler with an SCR output (Ul) and an LM3909 LED flasher (U2). It is connected to the phone line in the same manner as any extension phone. A ring signal on the telephone....

The design consists of an amplifier, a double-pole changeover switch and two loudspeakers: one for the master station and..

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 saturated state via R4. The dc switch is turned off via a negative voltage above that of the zener....

This 49-MHz FM transmitter consists of an audio amplifier, a low-pass filter, three RF stages, and a regulated-dc power supply. The output is about 16 mW into a 50- load. This transmitter can be used in many 49-MHz applications, such as in a baby monitor,....

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 off-hook the load current flowing in the telephone causes the voltage to fall below 5 volts dc.....

Tones (from the DTMF) on the telephone line are detected by Ul. When a valid tone is received, pin 14 (D..

This encoder uses a single contact per key keyboard and provides all other switching function electronically. The diode between terminals 8 and 15 prevents the output going more than 1 volt negative with respect to the negative supply V-..

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 power line...

The ac ringing voltage (typically 40 to 90 V at 26 Hz) is rectified by U1, the tone-ringer IC, and is used to drive ..

This switch uses four CD4013 BE dual flip-flops, an inverter, and an optoisolator to drive a triac. The circuit can switch 25-A ac load current. A standard 4x3 telephone keyboard is used to enter a 6-digit code. In case of a wrong code, a signal is....

This system uses a transmitter at around 100 kHz (see Fig. 86-3(a)) to control a remote rece..

A large number of intercom stations can be tied together. All units are connected in parallel, and the entire system is buzzed by only one signaling circuit. Each unit is powered individually from 1.5-V cells for redundancy. For greater signal volume, 3-V....

The dc voltage present on a telephone line is usually around 45 to 50 V on-hook and 6 V off-hook. This circuit uses This drop in voltage to activate a relay. The relay controls a cassette tapeTecorder...

The circuit receives its power from a 15-V wall adapter (not shown). The circuit takes advantage of the fact that th..

The two neon bulbs will light when more than 100 V is across the ringing circuit. The bulbs provide line isolation between the unit and the telephone line. Finally, they act as a voltage divider for the bridge rectifier made up of D 1 through D4. That....

This circuit shows the TP5700 directly interfacing to a low-voltage DTMF generator. VREGt supplies the necessary 2-V minimum bias to enable the TP5380 to sense key closures and pull its mute output high. VREGt then switches to a 3-V regulated output to....

A small neon lamp is triggered into conduction by the telephone's ringing voltage, passes just enough current to activate the LED in optocoupler Ul, which in turn triggers the 6-A Triac that controls 12—a 117-Vac lamp or bell. (Capacitor Cl is necessary....

This circuit flashes an LED to indicate that your phone rang during your absence. A differential amplifier with hyste..