# Minimum value of resistance

hello, i want to know can an arduino sense resistor values in mili ohms? by voltage divider circuit?

Would that be 1milliohm or 999milliohms and to what resolution would you want to measure.

less than 1 miliohm. until 0,5mohm

No, not by voltage divider. Why do you need to measure 0.001 ohms?

Noraiz: i want to know can an arduino sense resistor values in mili ohms?

by voltage divider circuit?

Sure.

No.

Just send 1000Amp through your resistor. That will result in 1volt per milliohm The Arduino can measure that. Leo..

'Just send 1000Amp through your resistor.'

I hope your resistor is a big one, or it'll get quite hot.

Allan

1000amp?? how it can be possible..

0.001 ohm is a solid rod of copper as long and thick as a pencil. Not easy to measure without some serious current and a kelvin connection. Is this a current shunt? Leo..

i want to calculte a resistance of copper traces on a PCB. which i expect to be in mili ohms.

There are lots of online calculators for circuit board traces. http://circuitcalculator.com/wordpress/2006/01/24/trace-resistance-calculator http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/ Leo..

Pass 1A along the trace, measure the voltage difference with a multimeter (it will be microvolts or millivolts), compute the resistance.

Thin PCB traces will warm up with 1A flowing, increasing the resistance. Very fine trances might overheat, try 100mA if unsure.

Having a current limited power supply makes this sort of thing easy (setting a constant current).

Alternative is use something like a 10 ohm power resistor in series with a low voltage supply to produce a suitable current, but you'll have to explicitly measure the current (measure the voltage across the 10 ohm resistor for this). In effect you have a voltage divider with 10 ohms and the pcb trace.

Tables of pcb trace resistance for standard plating thicknesses are available online. Copper always has a resistivity close to 1.7e-8 ohm-m, so you can calculate the approx resistance from the dimensions easily enough.

and thats the question how can i give 100mA from arduino or if use separate power supply how it can be connected to the arduino to pass 100mA current?

MarkT: Very fine trances [sic]

I've had some of those, but the less said the better ;)

Why would you need to know the resistance of a particular track to accuracy better than the calculations recommended above would give you?

And if you need to pass a high current, there are industry standards for track width and thickness - track spacing as well for high voltages.

Allan

Noraiz: and thats the question how can i give 100mA from arduino or if use separate power supply how it can be connected to the arduino to pass 100mA current?

100mA will drop 100uV across a 0.001ohm trace. Way too small for Arduino's 10bit A/D to detect. You need at least 10x that current to even see one A/D step. Leo..

Or read the V drop across the trace during a short high current pulse (not long enough to heat or magnetic field to jerk it loose). Risky but ...? :o