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Topic: How to measure Current being drawn by Arduino Platform (Read 2 times) previous topic - next topic

CrossRoads

You address out of range when the question comes up of what voltage is being measured - if <=5V, no problem.  If >5V, add some voltage divider resistors to bring the value down into the 5V range.
Until told otherwise, I'm going with the power is being measured going into the 5V pin as that is how I run most of my designs - either from USB power, or a 5V wallwart.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

MarkT

If the shunt is low side the Vlow is negative, if its high side you can use a voltage divider, but your formula made no allowance for that!

Commonly you would want some gain too as the voltage across a shunt is likely to be low (to avoid dissipation and efficiency issues) - using an op-amp as differential amplifier then provides whatever gain you need and will work with out-of-supply-range input voltages.
[ I won't respond to messages, use the forum please ]

CrossRoads

Unless the system is using +/-12V or something, how would you get negative? Kinda lost me there.
Measure both sides, take the difference, divide by the shunt value.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

gardner


Unless the system is using +/-12V or something, how would you get negative? Kinda lost me there.
Measure both sides, take the difference, divide by the shunt value.


If the shunt is placed on the negative supply side, the shunt voltage will be negative relative to the ground and negative analogue reference of the Arduino.

CrossRoads

Ok, so lets clarify the discussion here as a starting point.
In the example I assumed 9V battery and resistors with appropriate value to not exceed the Analog input.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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