Telephone Tapping Indicator

This simple circuit can indicate a misuse or tapping of Telephone line through a loud alarm. The circuit is too simple and can be easily assembled on a common PCB. Line voltage of Telephone lines is around 48 volts DC in the On hook state. When the handset is lifted, this voltage reduces to 12 volt DC. This change in voltage level is used to activate the circuit.When the switch S1 is closed, circuit becomes active and the telephone enters into the armed state.

The high volt DC from the telephone line passes through R1 and VR1 and bias T1 into conduction. As a result, the collector of T1 goes to ground potential to inhibit T2 from conduction. Buzzer and LED thus remain off. When the handset is lifted, the DC voltage from the telephone lines drops to 12 volts. This turns off T1 and T2 conducts. Buzzer beeps and LED lights indicating that the telephone is using.

Telephone Tapping Indicator Circuit

Setting
Connect the circuit to Telephone lines using a telephone plug. The free socket of the telephone or Caller ID can be used. Close S1 and adjust VR1 till buzzer stops beeping. Lift the handset. Buzzer should sound. Otherwise, just adjust VR1 till buzzer beeps.

Read More..

Analog Signal Transmission Over Telephone Lines

This is a circuit for telephone line is designed to carry audio signal, which is an alternating current in nature. To transmit measurement signal, which has very low frequency or DC signal, we have to convert the signal into AC with acceptable frequency range for telephone line transmission. This is the figure of the block diagram circuit;

For transmitting analog data over telephone lines, its ideal to use the TC9400′s square-wave output. Since the square wave takes up less frequency spectrum a square wave is actually preferred over a pulse waveform for data transmission. By use of low pass filters, the square wave’s spectrum can be further reduced. The TC9400 converts the frequency signal back into a voltage output linearly proportional to the original input voltage at the end of the telephone line. [Block diagram source: Microchip Application Note]

Read More..

Telephone Wire Single Pairtelephone Wire

Example Of A Correctly Wired Wall Jack.



Telephone Wire Single Pair 0 5 Mm Telephone Wire Two.



Telephone Jacks Mount The Telephone Jack.



Wire Pair 3 Line 3 Blue Wire And White Wires.



Telephone Wire Connectors Telephone Wire.



Telephone Wire Twisted With Spiral Stock Photo 43793233.



Guide To Rewiring Internal Uk Phone Wiring.



Data Telephone Wiring Standards.



Cable Modem With Either Airport Extreme Or Time Capsule Macrumors.



Telephone Cable Tc 001 China Telephone Cable Telephone Wire.

Read More..