Error Detection

Thread Starter

rama1

Joined Nov 9, 2011
2
Hi guys ,

I'm new to this forum .and i'm new to Engineering .

I'm working on alarm system which i will use it for sending SMS After wire broken or any other failures . for now , i'm wondering how would u know if an output wire connected to my PIC is broken .

Any reply will be helpful .

Thanks.
 

ErnieM

Joined Apr 24, 2011
8,036
What are these wires doing before they break?

A sketch of your concept would be helpful to get anything relevant to your problem.

And welcome to the Forums! ;)
 

Thread Starter

rama1

Joined Nov 9, 2011
2
Well , thanks for reply .

the wire is connected to pin and it always signal 5 volt to LED for example.

I want detect if some body cut this wire , so he will break the system .

thanks
 

ErnieM

Joined Apr 24, 2011
8,036
OK, so you have a wire with 5 volts on it. It can get the 5 volts from either the power supply (which will make the LED always ON) or from an output (so you can blink the LED).

Either way, you wrap this wire around your "secure area" and back to the PIC. At the PIC end, place a resistor (say 10K to 100 K) from the wire to ground, and the return end of the wire to a PIC input. When all is well there will be 5 volts on the input and the PIC will read a ONE there. If the wire breaks the resistor insures the voltage goes to zero and the PIC will read a ZERO there.

Of course, if you are blinking the LED you can only test the input when the LED is on.
 

RiJoRI

Joined Aug 15, 2007
536
Ernie's method will catch opens, but not shorts. The method we use is a 2K end-of-line* resistor, with a 2K on-board resistor, creating a voltage divider. The signal is sent into a comparator, and decisions are made from that.

--Rich
*End-of-line resistor: a resistor placed in the detection loop, physically located beyond the last device on the loop.
 
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