Hi guys,
I want measure resistance of the order 0.1 from arduino, how does this?
Thanks.

 

Put a known current through the resistance and measure the voltage across it -- or apply a known voltage and measure the current through it. Use electronics as needed to scale the quantities involved to useful levels.

 

I will assume the units are ohms. You should always give the units. (You could mean milliohms or Megohms etc. ) If it was a high power resistor you could use a constant current source of say 20 amps and measure the voltage across it using one of the arduino's ADC inputs. NOTE this would dissipate 40 watts in the resistor. A more realistic method would be to use a much lower constant current source and amplify the small voltage developed across tha resitor using an op amp. More background information would help us to suggest appropriate solutions.

Les.

 

hi, i have the same question to ask , how to measure ressitance

 

Buy a DVM...

 

I am puzzled how an "Electrical enginneer" (From profile for post #4.) has got by so far without being able to measure resistance.

Les.

 

Hello,

Have a look at this project:
10 ma to .01 ohm resolution DVM adapter

Bertus

 

That's a nice solution to the original TS's question.

Les.

 

I am puzzled how an "Electrical enginneer" (From profile for post #4.) has got by so far without being able to measure resistance.

Les.

Thread starter also claims to be "Electrical engineer." Why only pick on author of post 4?

 

I was assuming that the TS knows how to measure resistance using a DVM but did not know how to use the ADC voltage reading to get the value of a low value resistor. I find it difficult to beleive that an electrical engineer has never had to measure resistance even if it was only to check continuity or insulation.

Les.

 

I was assuming that the TS knows how to measure resistance using a DVM but did not know how to use the ADC voltage reading to get the value of a low value resistor. I find it difficult to beleive that an electrical engineer has never had to measure resistance even if it was only to check continuity or insulation.

Les.

Increasingly there are electrical engineers that have never had to measure resistance at all (or voltage or current or anything else) because the program they graduated from eliminated all hands-on labs in favor of computer-based simulation -- and then patted themselves on the back and got a paper or two published about their forward-thinking approach to engineering education.

 

That's a nice solution to the original TS's question.

Les.

I don't think it's the entire solution. Assuming the TS means measuring resistance that are in the 0.1 Ω range, then a 10 mA source would give a voltage of only 1 mV. Assuming it would be nice to get a measurement that's good to 10%, that means your ADC needs a resolution of 0.1 mV. How does that compare with the Arduino's capabilities (and here it matters what the actual capabilities are in practice, not what the marketing blurb claims).

I think he's still going to need to use a suitable amplifier, as well.

 

Increasingly there are electrical engineers that have never had to measure resistance at all (or voltage or current or anything else) because the program they graduated from eliminated all hands-on labs in favor of computer-based simulation -- and then patted themselves on the back and got a paper or two published about their forward-thinking approach to engineering education.

Yikes!

 

Increasingly there are electrical engineers that have never had to measure resistance at all (or voltage or current or anything else) because the program they graduated from eliminated all hands-on labs in favor of computer-based simulation -- and then patted themselves on the back and got a paper or two published about their forward-thinking approach to engineering education.

So true. So sad.

 

hi, i have the same question to ask , how to measure ressitance

@Lily Sheng
Do mean how to measure resistances in the 0.1 Ω range with an Arduino? Or just how to measure resistance in general? Or something in between?

If it isn't the first, then you are hijacking the Thread Starters thread and that will likely lead to a lot of confusion. But the fix is easy -- we can split off your post and give it it's own thread so that the content can more directly address your situation.

 

Hi guys,
Yes i want mesuare resistor from adc pic microcontrolor or arduino so i need the circuit from that

 

Several years ago I suddenly had to come up with a reliable method of verifying that the injector harness on a V8 engine had all of the injectors connected, two sets of 4 injectors, each about an ohm, in parallel, in each bank. This was a challenge because the connection wires were quite a few feet long. This was a 100% check production tester for a major US auto company. So the requirement was "perfect reliability and easy maintainability", as well as being cheaper than the previous method. My solution was to create a 4-terminal resistance meter. I used an LM7805 power tab regulator to supply100.0mA, and a o-199.9 millivoltmeter to read the voltage drop across the harness terminals.A digital comparator checked that the reading was within the specification for the 4 injectors in parallel. If the analog input has adequate resolution on that arduino, it could be used for the same purpose. But you must have a fairly low noise voltage supply and you will need to calibrate the current source. And it does demand a 4-terminal connection. BUT it is cheap, easy, accurate, and reliable. That company still sells that product now, 28 years later, and the auto plant used it until they revised that whole line for a different engine.

 

I don't think it's the entire solution. Assuming the TS means measuring resistance that are in the 0.1 Ω range, then a 10 mA source would give a voltage of only 1 mV. Assuming it would be nice to get a measurement that's good to 10%, that means your ADC needs a resolution of 0.1 mV. How does that compare with the Arduino's capabilities (and here it matters what the actual capabilities are in practice, not what the marketing blurb claims).

I think he's still going to need to use a suitable amplifier, as well.

By default, the Arduino (Uno) can measure 0 to 5V based on a 10 bits scale (so, approximatively, 0.5mV precision).

 

I would look to use an HX7111 which is commonly used to measure the resistance modification of a strain gage (to indirectly measure a weight). In your case, you are looking for the resistance value itself, not, indirectly, a weight, but I imagine that would be a relatively simple task to modify the various existing code, on Arduino, for the HX7111 modules, INCLUDING zero-ing the resistance (of any extra resistance in series of the circuit itself).

 

It is HX711, not HX7111. Sorry.