Creating A Wire Cut Detection

Discussion in 'General Electronics Chat' started by ajm113, May 16, 2012.

  1. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Hello I want to create a wire cut detection circuit for my micro controller and I'm not sure the what the best way is to do this without frying my microcontroller out.

    This is basically how I kinda imagine it working:

    Pump 24v through a line (since the line is maybe going to be going longer then 100 ft).

    Have a EOL resistor of 4.7k at the end of the line and have my trigger/switches in paralleled within the line and of course have a 100 1/4 watt resistor in series.

    Then have a some sort of ADC circuit that takes the 24 volts drops it down to 5 and gives us 3 pin binary outputs of the lines state based on voltage output.
    2= We are okay, 0 = Line was cut, 3 = Alarm.
     
    Last edited: May 16, 2012
  2. bertus

    Administrator

    Apr 5, 2008
    15,634
    2,342
    Hello,

    Can you post a schematic of the idea?
    That way we can see how to improve it.

    Bertus
     
  3. #12

    Expert

    Nov 30, 2010
    16,246
    6,738
    It generally works better to send a constant current into the wire and see what the resulting voltage is...but I'm just guessing. Think about whether a constant current will give you usable results.
     
  4. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Okay this is kinda how I imagine it working.

    I know the sketch is a bit crummy, but I kinda ran through it.

    The ADC basically outputs a binary format of the current state the wire is in encase if your wondering.

    EDIT: I have the same idea #12, it's just I want to make or use a some sort of ADC circuit or drop down voltage circuit that wont damage the PIC. Now if I get a some sort of drop down voltage circuit that takes the 24v and converts it to 5v and have it so if 24 drops down to half, I would get 2 volt output instead from the voltage converter for a ADC pin on my PIC.

    I've posted my voltage divider, but idk if it would be considered, a safe alternative.
     
    Last edited: May 16, 2012
  5. #12

    Expert

    Nov 30, 2010
    16,246
    6,738
    This will give you 19 milliamps that never goes above 5 volts.
     
  6. Sparky49

    Active Member

    Jul 16, 2011
    834
    417
    There is a tool called a Time Domain Reflectometer which does exactly what you are asking for.

    I made one here:
    http://forum.allaboutcircuits.com/showthread.php?t=67329

    I'm not very good at programming, but I'm sure you could program it to understand a reflected pulse indicates a break?

    TDRs can also judge distance to the break. With a bit of maths, your chip can tell you roughly where the cut is. :)

    I think the theoretical 'range' of my project was about 2.5km!
     
  7. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Thanks #12, I'll give your circuit a try, I just need one zener, but Radioshack doesn't have one that fits my watts range, I need one at least 1/2 watts for testing reasons or if I decide to use it on something else. I don't suppose anyone knows who gives free samples of Zener Diodes?
     
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