# Arduino - measure voltage and amps



## Biostudent (Jul 13, 2010)

Hi everyone,

I am looking for some help on an arduino project I am working on. I've seen a little info here and there, but I haven't been able to find a circuit design or something similar for monitoring high voltage, or current, with an arduino.

Does anyone have a link to anything I could use for monitoring 100-200 volts with my arduino? 150-200 would work too. 

Someone told me a hall-effect sensor would work...something like this:https://www.sparkfun.com/products/8882

Im not sure how to set it up with the voltage I want to measure, 150-200. 

I'll be working on a special android app that works along with the arduino device. So, any help with this part and I'll make sure to let you have the app to play around with on your project. 

Thanks!


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## crackerjackz (Jun 26, 2009)

The emw chargr already does all this and much more look at the schematics and just recopy the voltage and current sensing ...


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## Biostudent (Jul 13, 2010)

Hey,

Thanks for the tip. I've never seen that device before. I haven't been keeping up with the latest. I'll see if I can find the schematic. Is it on the forum? If you have a link that'd be awesome. Otherwise I'll find it. Thanks again


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## mk4gti (May 6, 2011)

FYI The EVDisplay (cleanpowerauto.com) has all of this in a nice package that is affordable.


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## Biostudent (Jul 13, 2010)

mk4gti said:


> FYI The EVDisplay (cleanpowerauto.com) has all of this in a nice package that is affordable.


Yes I know about the EVDisplay. I'm looking to develop my own device. It's going to have custom features, and I need to build it myself in order to get them all. I'm trying to learn more about electronic hardware development. It's fun 


http://emotorwerks.com/tech/electronics <-- wow super awesome. Thank you very much for the link. I love it.


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## ga2500ev (Apr 20, 2008)

Biostudent said:


> Hi everyone,
> 
> I am looking for some help on an arduino project I am working on. I've seen a little info here and there, but I haven't been able to find a circuit design or something similar for monitoring high voltage, or current, with an arduino.


There's really nothing special about the arduino in this area. You'll probably get more hits if you expand your search to microcontroller instead of just arduino.


> Does anyone have a link to anything I could use for monitoring 100-200 volts with my arduino? 150-200 would work too.


It's done exactly the same way that a voltmeter does it. As explained in this tutorial voltmeters generally have a very limited range of voltages they can actually measure. In the same page the full range is a mere 200mV.

To get other ranges, the input voltage is divided by a precision resistor divider network to limit the measured voltage to the range of the measurement device. The arduino generally can measure based on the supply voltage (5V), the internal reference voltage (generally 1.024V), or from an external voltage reference. Several comp anies such as TI, Maxim, and microchip all have precision 4.096V voltage references. That voltage is chosen because it's a power of 2 and so the voltage step between ADC values is precise. For example the arduino has a 10 bit ADC with 1024 steps. So with a 4.096V reference the voltage between steps is exactly 4 mV. Whereas if the 5V power supply is used the voltage step is 4.8828 mV. A lot more difficult to compute with.

Finally the precision external reference is useful because it stays the same no matter the input supply voltage. If your power supply happens to be 5.12V for example, then all your measurements would be off by nearly 2.5%.



> Someone told me a hall-effect sensor would work...something like this:https://www.sparkfun.com/products/8882


Hall effects are one way to measure current, not voltage.



> Im not sure how to set it up with the voltage I want to measure, 150-200.


Voltage divider into an opamp voltage follower tha goes into the ADC of the arduino.

To be on the safe side you really need to isolate your arduino from the high voltage. This is typically done using a linear optocoupler such as the IL300 or the TL494.


> I'll be working on a special android app that works along with the arduino device. So, any help with this part and I'll make sure to let you have the app to play around with on your project.
> 
> Thanks!


Sounds like fun.

Good Luck

ga2500ev


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## frodus (Apr 12, 2008)

Search for voltage transducer. There are some that have a 0-5v output for a 100/300/600v input and are isolated.


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