Alarm phone wire disconnected

[Li_ereunpisan]

I want to design an alarm phone cord ....
by way of working:
example the distance from the central telephone to the house within 1km, if among all these 1km there are disconnected, for example in the 300m point the alarm will active

how to detect it using uController , what could they?
because I was inspired with a TDR (Time Domain Reflectometer), which can detect disconnected cables to distances of several miles

 

[betwixt]

It would be much easier to detect the residual line current. The current will be in the region of 30uA for an on-hook (not in a call) phone and >50mA if it is in a call. If the line is disconnected it will fall to almost zero.

The problem with TDR on a phone line is that you will get a reflection from every change in impedance along the line so the signal will be chaotic to say the least.

Brian.

 

[Li_ereunpisan]

@brian
in my opinion .. even though the state again on hook or off hook, if there are disconnected cables, still detectable...
supposing here .... how do I detect broken wires within a few miles? let's just where cable is not connected where

 

[betwixt]

I think you need to conduct experiments to see if TDR is a feasible solution. It will certainly reflect from an open wire but it might be very difficult to tell the difference between the broken end and other impedance mismatches. Especially over long distances there will be reflections off other reflections so the longest delayed one will not necessarily indicate the one furthest away.

Brian.

 

[Li_ereunpisan]

I think you need to conduct experiments to see if TDR is a feasible solution. It will certainly reflect from an open wire but it might be very difficult to tell the difference between the broken end and other impedance mismatches. Especially over long distances there will be reflections off other reflections so the longest delayed one will not necessarily indicate the one furthest away.

Brian.

oh of course TDR is a tool that has been tested .. because I have done so by detecting broken(fault location) wires in the under ground .. that the cable along the 800m, then I know the cable was broken at the point of 600m, it indicates that the TDR is a good example of a tool to design my project

wandi