General • Pico 2 ADC issue

Dear community,

I want to measure the current drawn by a DC motor, using the Raspberry Pi Pico 2 ADC. The motor is driven using a DRV8874 from Texas Instrument, which integrates a current sensing feature. (see DRV8874 datasheet §8.2.2.2.1 and §7.3.3.1 https://www.ti.com/lit/ds/symlink/drv88 ... 53Ddrv8874).
The schematics of the setup I implemented is attached.

When I command the motor to spin, I am able to read a voltage measurement of the Ipropi signal using a voltmeter (proportional to the motor current). However, the Pico ADC reading remain a flat noisy signal with a small offset (expected, as explained in the Pico datasheet §5.3 https://pip-assets.raspberrypi.com/cate ... ion=inline).

- I tested all the connexions of my circuit: no floating pin, continuity is OK everywhere
- The Pico and the DRV8874 share a common GND.
- I tested my hardware and implementation of the ADC reading logic using a simple potentiometer connected beween GND and GPIO26: the ADC reads correctly the voltage variation when I manually change the resistance.
- The Ipropi signal can be at maximum 3.45V, i.e less than the maximum value behond which the voltage would 'leak' through the diode into the IOVDD rail (according to the Pico datasheet §5.3)

Why don't I read the same signal as seen by the voltmeter? Please let me know what you think, and don't hesitate to ask me for complementary informations (I tried to be as detailed as possible).

Statistics: Posted by timoulebesto — Sat May 02, 2026 8:58 pm

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