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Topic: Arduino as an ammeter (Read 19405 times) previous topic - next topic

jgalak

This may be a basic question, but I'm wondering if there's a way to use the arduino as an ammeter.  I know that I can use an analog input as a voltmeter, but how can I measure current without significantly impacting the rest of the circuit?  Obviously I'd have to interrupt the circuit to insert the "test leads", but how do I set things up so that the arduino (and attendant circuitry) doesn't change the resistance in the circuit being measured?

Thanks,
jgalak.

bilbo

Google really should have yielded some results, but take a look at this: http://en.wikipedia.org/wiki/Shunt_%28electrical%29
Do some reading on Ohms law while you are at it.
Essentially, you will measure the voltage across the shunt with the arduino's ADC, and use that to figure out the current.

RuggedCircuits

Much depends upon the range of currents that you want to measure. For "big" currents a popular thing is the ACS712 and cousins:

http://www.allegromicro.com/en/Products/Part_Numbers/0712/

You can probably find this on breakout boards if necessary. For "small" currents a high-side current sensor makes it easy without fussing with precision op-amps:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ZXCT1009FCT-ND

Both of these devices convert current to voltages that you can then read in with an analog input.

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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

lxmyers

Not sure if this is relavent but if you are interested in non-invasive current sensing of mains AC, Sparkfun have a current clamp that works quite well.

http://www.sparkfun.com/products/10341

There's also a pretty cool page on how to get it working with the Arduino http://openenergymonitor.org/emon/node/58

jgalak

Ah, ok, got it.  I was aware of shunts in general, but not that they could be used as very-low resistance devices for this type of purposes.  I will have to investigate this further.

I am looking at small currents - mAs, no more.

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