Cut Phone Line Detector

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

1. R1, R2, R3 (22 M 1/4 W Resistor).
2. R4 (2.2 M 1/4 W Resistor).
3. C1 (0.47uF 250V Mylar Capicitor).
4. Q1 (2N3904 or 2N2222 Transistor).
5. Q2 (2N3906 Transistor).
6. Q3 (IRF510 Power MOSFET).
7. D1 (1N914 Diode).
8. Load (see notes).
9. Misc (Wire, Phone Connectors, PCB).

Notes

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.

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.