This cut phone line detector circuit is used to detect whether your phone line is active or not.
R1,R2,R3 = 22M Ohms
R4 = 2.2M Ohms
C1 = 0.47uF/250V Mylar caps
D1 = 1N914, NTE519, or other small signal diode
Q1 = 2N3904, NTE123AP
Q2 = 2N3906, NTE159
Q3 = IRF510, NTE2382, MosFet
This kind of circuit speaks for itself. While the phone line is okay, Q1 works as a short that has a extremely high resistance/ohms value via R1, R2, and R3 for a total close to 66 MegaOhm, so it is very high. When the phone line is cut (open), it triggers the MosFet (Q3) via transistor Q2 to drive the load. Replacements are acceptable, not one of the parts are crucial.
The ‘LOAD’ can be anything you like. A lamp, relay, motor, tape-recorder, stereo, security system, or anything else.
Remember that telephone providers do not like to have anything ‘directly’ connected to their wire connections for apparent reasons, so work with this circuit at your own risk. If you want to experiment with it safely, work with an Opto-Isolator or something…
Circuit designed by Tony van Roon