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Topic: Simple Arduino ohm meter & upload reading on the fly to hp via wifi shield (Read 972 times) previous topic - next topic

keithlee

Hello Guys,

I'm wonder if anyone could help to provide guidance on how to turn an Arduino to an ohm meter that can perform the following task;

a) Performing 2 wires resistance measurement.
b) with minimum one output channel for a single resistance measurement.
c) resistance measurement range (1K ohm to few hundreds Mega ohm)
d) Measurement can be triggered via a handphone apps to initiate Arduino to perform the measurement.
e) upon making the resistance measurement the result can be automatically transmitted out to hand phone via either Wifi or GSM or wireless shield

Thank you guy and look forward to you expertise advice soon. :)

jremington

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c) resistance measurement range (1K ohm to few hundreds Mega ohm)
This wide range is very difficult to cover with an Arduino and would take a fair bit of external circuitry. It is an unrealistic requirement. Have you researched how to measure resistance with Arduino?

Overall a very challenging project.

DVDdoug

That's not an easy project.

I've never done anything wireless but either Wi-Fi or GSM should work.   Of course, you'll need to write a phone app too.   If you use GSM, the Arduino is going to need a cell phone account.

A 4-wire resistance measurement is pretty straightforward.   You just run the current source separately from your voltage measurement.

Have you done any Ohm's Law calculations and considered the voltage & current you want to use?     You'll need to build a constant-current source and then measure the voltage and calculate resistance with your sketch.   

I'd suggest starting with a "simple" resistance measurement range, say between 1K and 10K Ohms.

The Arduino can measure 0-5V.  The analog-to-digital converter is 10-bits (0-1023 decimal) so with the default 5V reference you get 5mV resolution and with the optional 1.1V reference you get 1mV resolution.   

To cover the range of 1K to hundreds of Meghoms, you'll most-likely need multiple ranges to keep the voltage requirements within reason.   That would mean changing the current source and possibly the the voltage reference if the reading gets out of the ADC range.

And of course, the meter circuit generally needs an isolated ground.    The "wrong" ground connection between the meter and the circuit under test will invalidate any measurements.  (And the circuit under test can't be powered-on during the resistance measurement.)

     

keithlee

Thank you so much Jremington for your reply.

Yup. In fact I did some test based on the following circuit schematic and surprisingly it worked for a single range resistance. To extend to a wider resistance coverage it would definitely requires an external circuitry.

http://learningaboutelectronics.com/images/arduino-ohmmeter-circuit.png

Besides the difficulty of developing an external circuitry, i have also no idea how to trigger or initiate the measurement via a hand phone apps and transmit the measurement back to hand phone apps.

Do you mind to share more about which is the most effective communication mode (wifi, wireless, GSM) for the above task.

Your input is highly appreciated. :)

keithlee

DVDdoug , Thank you so much for your input specifically on the ohm meter measurement circuitry theory.

To communicate with Arduino board via wifi shield, do you have any sample codes or guidance on how to send a trigger to Arduino via a hand phone and also transmitting the reading back to hand phone. I believe it require to setup a web server to act as a interface or handshake between the hand phone apps and the arduino board. please correct me if i'm wrong.

 

jremington

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Do you mind to share more about which is the most effective communication mode (wifi, wireless, GSM) for the above task.
None of these methods are trivial to implement, but all will work and there are tutorials for all of them. You need to decide exactly what you want to do, and approach the overall problem one bit at a time.

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