Cut Phone Line Detector

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

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.