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ACS724 Current Sensor noise

Just got the ACS724 and have tried it in series with the 1212, the MCC33926 motor driver board outputs which are powering a 25D metal gear motor. The current feedback from the motor control board is very noisy, I’m not able to get resolution better than .1 amp which is a problem for my application.

I’m using an Texas Instruments MSP430FR2311 MCU to calculate RPM and do the DAC and it’s connected to a Raspberry Pi 3B+ via UART. Everything has a common ground. I tried the ACS724 with the 5VDC from the pi and from the MCU. The problem that I’m having is that the ACS724 is actually a lot noisier than the feedback from the motor control board. I’m not sure why that is? I tried a capacitor but that didn’t make any difference. I have attached a sample waveform from my scope.

Hello,

Could you post some pictures showing how you have everything connected and how you’re probing the output of the current sensor? Which version of the ACS724 current sensor do you have?

Kevin

This one died on the vine. I see from the datasheet, this noise is normal. This board is designed to read the top end of the current scale, not in the under 1A range I suppose. If you add a capacitor, you get less noise, but the rise time increases. I need to sense a 60mA, 6ms pulse. So the device at rest draws .25A and I need to sense when it rises to .85mA and measure to see that it was 6000us or more. I can either measure DC and the input of my board, or would maybe prefer to read a 12V square wave output. Can you help?

Hello, FlightRisk.

As you said, these sensors are optimized for measuring currents in the range of several amps to tens of amps, so it might be challenging to measure small currents like what you’re describing. Is your pulse 60mA or 600mA? (You wrote 60mA first, but the difference between 0.25A and 0.85A is 600mA.)

I’m not really sure what you mean by “I can either measure DC and the input of my board, or would maybe prefer to read a 12V square wave output”, but if you describe more about what you want to do and what you are using to read the sensor, we might be able to offer some suggestions.

Kevin