Category: Main page » Telephone

Cut Phone Line Detector

Source: http://www.aaroncake.net/

A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn't take me long to find this circuit in Electronics Now. When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system.

Schematic


This is the schematic of the cut phone line detector

Parts


Part

Total Qty.

Description

Substitutions

R1, R2, R3

3

22 Meg 1/4 W Resistor

R4

1

2.2 Meg 1/4 W Resistor

C1

1

0.47uF 250V Mylar Capicitor

Q1

1

2N3904 Transistor

2N2222

Q2

1

2N3906 Transistor

Q3

1

IRF510 Power MOSFET

D1

1

1N914 Diode

Load

1

See "Notes"

MISC

1

Wire, Phone Connectors, Circiut Board

Notes

1. The "Load" can be a relay, lamp, motor, etc. The circuit can also be connected to a security system to sound an alarm in case the phone line is cut.

2. If the circuit is connected to a security system or other circuit, both circuits must be electrically isolated from each other using an opto-isolator, relay, etc. This also means that the Cut Phone Line Detector must be powered by a seperate 9V supply.


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