Wireless Telephone Eavesdropper

The IR transmitter connects to a telephone circuit, and transmits both sides of all telephone conversations to any line-of-sight location, within 40 feet. No power is taken from the central office, as long as all phones remain on-hook. The current flows through the phone and back to the central office, thereby keying their equipment. We tap into the telephone line by connecting the IR transmitter circuit in series with either the tip or ring. When the telephone is off-hook, current will flow through the diode bridge polarity protector and supply the power for the IR transmitter. The phone's audio information is taken off the line by transformer T1. The 1000-W winding of the transformer connects to a two-stage transistor audio amplifier/modulator. A 2000-W potentiometer could be added to the input of the two-stage amplifier to control the modulation level, and another potentiometer could be added in place of R3 to adjust the
IR's idle current.

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Telephone Tone Ringer

This is a complete telephone bell replacement circuit with minimum external components with on-chip diode bridge and transient protection and direct drive for piezoelectric transducers.

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Telephone Tap

Amplify or record a telephone call with the simple circuit shown. The 8-W secondary winding of a miniature transistor output transformer is connected in series with either of the telephone lines. The 1000-W primary winding can feed either a cassette recorder or an audio amplifier.

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Telephone Ringing Detector, Frequency And Volume Controlled

With the 555 timer connected as a multivibrator and an opto-isolator, a remote speaker can be driven.

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Telephone Ringer Uses Piezoelectric Device

The electronic bell needs no power supply. Most of the resistors are not critical, although C2, R2, and R3 work best at the values given. Leaving out R1 will make the unit ring louder. The piezo buzzer may vary from store to store. If it has two leads, connect the red lead to the collector and the black lead to the emitter or Q1. If a third (blue) lead is present, connect it to base of Q1.

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Telephone Line In Use Indicator 2

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 of all phones on the line. Since the power for the circuit is supplied by the phone company, a circuit could be added to each phone as an off-hook indicator.

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Telephone Line In Use Indicator

When a telephone line is not in use, about 48 V appears across the line, which drops to about 10 V or less when the line is in use. This circuit switches a bicolor LED as an indicator.

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Telephone Line Tester

The telephone-line tester consists of nothing more than a meter (thats 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. When the circuit is connected to the telephone line, a meter reading of 5 to 10 V (when S1 is pressed) indicates that the line is okay.

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Telephone Intercom

Two telephones can be used as an intercom setup with this simple power-supply arrangement. The 500-W resistors maintain line balance.

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Telephone Hold Circuit

When S1 is pressed, the SCR fires, and places LED1 and R1 across the phone line. The line voltage drops to about 20 V, which holds the connection to the phone company's central office.

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Telephone Controlled Night Light

When the telephone rings, or when the handset is lifted, the night light is turned on and remains on while the conversation takes place. When the handset is replaced in the cradle, the light remains on for about 11 s. During standby conditions, the -28Vdc bias on the phone line maintains the output of U3 in a high state. When the ac ring signal is applied to the phone line, it is processed by the ring detector U1, producing a negative output pulse at pin 2 for each ring. These pulses trigger U2, causing its output to become high and the discharge transistor to turn off. The high output of U2 activates optoisolator U4, which turns on the night light. Each ring retriggers the timer and discharges C1, preventing it from reaching the 2/3 VDD threshold level. Thus, the night light will remain on while the phone is ringing and for about 11 s after the last ring. After 11 s, C1 will be charged to the U2 threshold level (2/3 VDD) resulting in
the U2 output returning to a low level and its discharge output turning on, discharging C1. The lamp will turn off if the phone is not answered.
When the phone is answered, a 1-KW load is placed across the phone. This removes the differential input to op amp U3, causing its output to become low, and capacitor C1 starts discharging through R1. As long as the voltage across C1 remains low, timer U2 cannot start its cycle and the lamp will remain on.
When the phone is hung up, the low impedance is removed from the phone line and the differential voltage across the line causes the U3 output to become high. This allows C1 to start charging, initiating the timing that will turn off the night light.

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Telephone Blinker

A small neon lamp is triggered into conduction by the telephone's ringing voltage, passes just enough current to activate the LED in optocoupler U1, which in turn triggers the 6-A Triac that controls I2-a 117-Vac lamp or bell. (Capacitor C1 is necessary only when the circuit is used to drive a bell.) The lamp will flash off and on at the ringing rate, which is normally around 20 Hz. If a 117 Vac bell is used, connect it in place of the lamp.

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Simple Touch Tone Generator

The oscillator is a Motorola MC14410CP chip using a 1-Mhz crystal. The chip generates both the high and low tones, feeding the energy to the amplifier through 1-K resistors and the 1-uF capacitor. Values for the output resistors can vary from a few hundred ohms to about 60 K ohms. The value of the resistor shunting the crystal can vary from about 3 to 15 Mohms. The amplifier consists of an LM-380N.

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Scramble Phone

IC-1 and the associated circuitry form a stable audio tone generator that feeds a buffer amplifier, Q1 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-D1 through D4-and T1 and T2. If the two transformers and the four diodes are perfectly matched (which is almost impossible to achieve and not necessary in any case) no carrier will appear at the input or output of T1 and T2. In a practical circuit, a small amount of unbalance will occur and produce a low-level carrier tone at the input and output of the balanced modulator. A telephone carbon mike and earpiece are connected to the low impedance winding of T1, with a three volt battery supplying the necessary mike current. Trim potentiometer R4 is used to make a fine frequency adjustment of the oscillator so that two scrambler units may be synchronized to the same carrier frequency. Rg limits line current to 25mA.

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Ringer Relay

When the phone rings, the ring signal from the telephone company lights a neon lamp within a CLM3120 optocoupler. That causes a drop in the resistance of the CdS cell output of the device, turning on transistor Q1. When Q1 turns on, relay K1 is energized. The circuit should be connected in series with the lamp that is to be activated.

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Portable Tone Generator

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Phone Recorder

This recorder can be connected to the telephone lines just about any place, and no external power source is needed. The tape recorder's switch terminals are applied to a pair of transistors, connected as Darlingtons, that are used to turn the recorder on and off. When the telephone is off-hook there's usually about 50 Vdc across the phone thats divided over R1, R2, and R4, so that Q1's base is negative enough to keep the recorder off. Pick up the receiver, and the voltage drops to 5 V. That leaves not quite-enough voltage on Q1's base to keep that transistor at cutoff, so the recorder begins. Remember to keep your recorder's switch in the on position, and depending on how many people use the telephone, remember to rewind or change tapes occasionally!

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Phone Light

When the phone does ring the triac is triggered into conduction by signal applied to its gate (G) through a switch (diac), D2. The triac acts as a switch, conducting only when a signal is present at the gate.

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Music On Hold Box

U1, an LS3404 melody chip is activated when "hold" S1 is pressed, which causes SCR1 to conduct and hold the telephone line via T1, R1, and LED1. The voltage across R1 and LED1 is used to activate the melody chip. Q1 and Q2 form a restart circuit to keep the melody chip going during hold.

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Music On Hold

With this music-on-hold device, you can answer the phone in one room, place caller on hold, and then pick up the telephone again at another location. When you pick up the phone the second time, you automatically deactivate the music-on-hold feature and can continue your conversation.

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