Cut Phone Line Detector

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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

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.

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Comments

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anonymous Cut Phone Line Detector Thursday, May 09, 2013 3:27:34 AM

hi. thanx for the circuit. is there a replacement for the MOSFET because i have to get it on the Ugandan market.

anonymous Cut Phone Line Detector Sunday, September 13, 2009 7:32:15 PM

Someone complained the resistor values being excessively high. The reason for that must be to extend the battery life. The circuit is not a good one as it draws significant battery current even when phone line is intact. Since the input impedances seen by the transistors are highly elevated, the circuit wil also be very sensitive to noise.

Gm Karutz Cut Phone Line Detector Friday, August 07, 2009 8:30:24 AM

is this device can be use in grounded telephone lines? if doesnt, please give me some schematic to detect grounded telephone line...thnx

priyesh jain Cut Phone Line Detector Tuesday, March 24, 2009 1:03:49 AM

This circuit is so easy for the students those work on the minor project and it is very useful to detect the phone tapper.

niraj kumar Cut Phone Line Detector Sunday, March 08, 2009 10:35:34 AM

this is vary good device.it is vary use full in our day to day life.please if posible send benchmark analaysis to my email .

ivy Cut Phone Line Detector Friday, July 11, 2008 1:40:24 AM

is this applicable in wider range of detecting the cut of a wire?

Mike Tarr Cut Phone Line Detector Wednesday, May 28, 2008 11:54:54 AM

Can I find a circuit already built?

anonymous Cut Phone Line Detector Tuesday, April 01, 2008 11:26:15 AM

its a good circuit but i want to find like that circuits when talking will start and circuits cut the line which are predefine by us for exaple after 5 mins,10 mins and etc. if u have a like this circuits please send it my email address on urgent basis email address is

kamran Cut Phone Line Detector Tuesday, February 12, 2008 11:28:34 AM

if i used the wirless phone it could be work and tell me how i connected with it and if you give me the more and more knowledge plz help me any one knows it thanks

revannath Cut Phone Line Detector Monday, January 07, 2008 3:51:05 AM

thank you, very good but sir could you please provides more information about this.

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anonymous	Cut Phone Line Detector	Thursday, May 09, 2013 3:27:34 AM
hi. thanx for the circuit. is there a replacement for the MOSFET because i have to get it on the Ugandan market.
anonymous	Cut Phone Line Detector	Sunday, September 13, 2009 7:32:15 PM
Someone complained the resistor values being excessively high. The reason for that must be to extend the battery life. The circuit is not a good one as it draws significant battery current even when phone line is intact. Since the input impedances seen by the transistors are highly elevated, the circuit wil also be very sensitive to noise.
Gm Karutz	Cut Phone Line Detector	Friday, August 07, 2009 8:30:24 AM
is this device can be use in grounded telephone lines? if doesnt, please give me some schematic to detect grounded telephone line...thnx
priyesh jain	Cut Phone Line Detector	Tuesday, March 24, 2009 1:03:49 AM
This circuit is so easy for the students those work on the minor project and it is very useful to detect the phone tapper.
niraj kumar	Cut Phone Line Detector	Sunday, March 08, 2009 10:35:34 AM
this is vary good device.it is vary use full in our day to day life.please if posible send benchmark analaysis to my email .
ivy	Cut Phone Line Detector	Friday, July 11, 2008 1:40:24 AM
is this applicable in wider range of detecting the cut of a wire?
Mike Tarr	Cut Phone Line Detector	Wednesday, May 28, 2008 11:54:54 AM
Can I find a circuit already built?
anonymous	Cut Phone Line Detector	Tuesday, April 01, 2008 11:26:15 AM
its a good circuit but i want to find like that circuits when talking will start and circuits cut the line which are predefine by us for exaple after 5 mins,10 mins and etc. if u have a like this circuits please send it my email address on urgent basis email address is
kamran	Cut Phone Line Detector	Tuesday, February 12, 2008 11:28:34 AM
if i used the wirless phone it could be work and tell me how i connected with it and if you give me the more and more knowledge plz help me any one knows it thanks
revannath	Cut Phone Line Detector	Monday, January 07, 2008 3:51:05 AM
thank you, very good but sir could you please provides more information about this.