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A current shunt is a resistor that can handle the full current of the motor. You would probably want a 0.1Ω resistor rated for at least 1 watt.

You measure the voltage drop across it to determine the current. The voltage will be quite low. With a 0.1Ω resistor and a 2A load, it will be 0.2V. You want to amplify that up closer to the full scale input of the ADC to get a decent resolution. An op amp with a gain of 10 would work well for that. Use a rail to rail op amp that can run from the 3.3V power supply.

Here is a schematic:
Schematic

R4, D1 & D2 protect the op amp input from any spikes the motor produces.

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boojumliussnark@lemmy.world ⁨1⁩ ⁨week⁩ ago
Sorry I forgot to ask: I should cut the SENSE-A connection to ground right?

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boojumliussnark@lemmy.world ⁨1⁩ ⁨week⁩ ago
Oh, wow!

Very nice! Thank you so much for doing this!

Is it correctly understood that the “Sense” line can be hooked up directly to the ADC input on the Pico?

Now, just because I am quite ignorant when it comes to all this, I will venture to ask: This is better because it is closer/faster/more exact than using the Hall current sensor, or? With my complete lack of understanding, I had the impression, that I could more or less “just” connect the sensor to the “right spots” and directly to the ADC input on the Pico, and my work in the Pico would be similar to this setup?

Don’t get me wrong - I can see this is much more elegant - and won’t be bothered by whatever else might use power on the same rail. But since it might be simpler for me to use a more “out of the box” component like the sensor, instead of my bad soldering of several discrete components… Also however ridiculous it might seem it is much easier for me to source 5 modules - than 5 of each of these components (I would have to buy many of each, and waste most).

So I have to ask. :-)

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- cmnybo@discuss.tchncs.de ⁨1⁩ ⁨week⁩ ago
  The sense output from the op amp connects directly to an ADC input. The output is 1 volt per amp. If sense_a is already connected to ground, you will have to disconnect it.
  
  The hall effect current sensor will work fine too. They do tend to have an offset, but you can calibrate that out in software. Just take a reading when the motor is off and subtract it from the reading when the motor is on. If you do use the hall effect sensor, you could connect it between sense_a and ground so it will only measure the motor current.
  
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  - boojumliussnark@lemmy.world ⁨1⁩ ⁨week⁩ ago
    Thanks again!
    
    Does this look OK, to your trained eye then? Image
    
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    cmnybo@discuss.tchncs.de ⁨1⁩ ⁨week⁩ ago
    Yes, that is wired correctly.
    
    Did you get the 5 amp current sensor or the 30? The higher current ones output less voltage per amp, which will make it harder to measure small currents.
    
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