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Hey guys, i need some help with designing a procesor to compare the resistance of a cable to approx a 1 ohm resistor. ie the 1 ohm resistor is the cable threshold. If the cable resistance is less then 1 ohm then an LED lights up.
Design a processor? You can't design a processor. Possibly an electronics circuit.
Anyway: Use a known voltage in series with a known resistor to feed the wire. The wire and the resistor will form a voltage divider. Measure the voltage over the wire.
With a 1k resistor, the voltage over the wire should be approx 0.001 of the input voltage. Below that, your wire is good. With 5V in, the wire is good if the measured voltage is below 5mV, and the 1k resistor gives a short-circuit current of 5mA through the wire.
If you want to measure the resistance, it takes a lot of resolution for the ADC, or you need an ADC that can be run with a low voltage for full-range measurement. Or you will need an OP-Amp to amplify the measured voltage before feeding it to the the ADC input.
If all you need is a good/bad reading, then you can skip ADC and processor and just use an OP-Amp as comparator. Just let it compare the measured voltage by applying a similar resistor 1/1001 division on the other input. Then, you don't even have to bother with a known reference voltage. Only the precision of the resistors will matter.