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.

 

Hello,

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

Bertus

 

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.

 

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.

 

This will give you 19 milliamps that never goes above 5 volts.

 

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!

 

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?