Pololu Robotics & Electronics
My account Comments or questions? About Pololu Contact Ordering information Distributors



Hi everybody,
i have a question about the ACX711EX. https://www.pololu.com/product/2453
I know the maximum current it detects is from -31A to 31 A. I wish to design a circuit that would detect the maximum current from 10mA to 200mA. Beyond this range, it should not do anything. Is it okay if I connect an opamp to it or may be a summing amplifier?

I was thinking instrumentation amplifier but then again instrumentation amplifier the inputs are differential.
Any ideas would be greatly appreciated.

Thanks a million times for your time.



In general, it seems like it would be not be trivial to obtain that kind of sensitivity from one of our current sensor boards.

What constraints lead you to select the ACS711EX over one of our other Allegro current sensors with a smaller sensing range? How far above 200mA do you expect your current to be? The IC on our ACS714 Current Sensor Carrier -5A to +5A board will tolerate a 100A pulse for up to 100ms (like the ACS711EX) and has a much higher sensitivity (185 mV/A) than the +30A to-30A ACS711EX board (45mV/A ) you mentioned.

In addition to electrical noise in your system, you should also be aware that the sensor might be susceptible to noise from stray magnetic fields. A magnetic coupling value is not provided in the datasheet for the ACS711EX sensors, but the ACS714 has a magnetic coupling of 12 gauss per amp.



Thank you so much for your prompt reply. While buying it, I was not sure if i need to go for the 5A option instead of 31 A as the boards offer. Now that I have the product, can I get a close value to the range I mentioned? when we got the spec sheet, we had to design a multimeter circuit to detect AC,DC current in the range 10mA to 200mA( can be±0.5mA).
So some of the questions are: 1. I have seem this board to be connected in series with the load to detect current, so can i make my own circuit with power supply and a resistor(a with ACX711 in series with it to detect( AC/DC- I understand for AC we need to sample to get RMS values).
The spec sheet also said AC current is 40- 100 HZ and seeing its high bandwidthof 100 KHz i chose this ACS711EX.

I would reorder a smaller range board but I just need an interim solution as the preliminary project demo is due in a weeks time and I just need to target the range from 10mA to 200 mA(-I interpret this as either higher/lower current than this might be supplied, but the circuit still detects within this range or strictly current in that range is supplied).

Thank you


A range of 10 mA to 200mA with only 0.5mA of error will be very difficult with this sensor board. With a 45mV/A signal from the ACS714 Current Sensor Carrier -5A to +5A sensor I mentioned, a 0.5mA change in current would only change the output by about 2 microvolts. Although I do not have any specific recommendations for one, if you are measuring AC current, you might look for a current sense transformer.