0
\$\begingroup\$

The first way I thought of was just a resistor directly in series with the motor and have an analogue pin before and after this resistor to find the voltage through (the 10-bit value of the first pin subtract the 10-bit value of the second, using a voltmeter I can calibrate and convert from 10-bit value to voltage) and since the resistance is known I can find the current.

The issue with this is that the resistor will change temperature and then the resistance will change, meaning we can no longer calculate the current.

So, what is the best way to find the current? "Best" meaning most accurate and without introducing many other factors.

The transistor driver I am using and the current I am trying to measure

\$\endgroup\$
6
  • \$\begingroup\$ Measuring current gets harder the lower you want the voltage drop. A pulsed "motor" current offers additional possibilities. \$\endgroup\$
    – greybeard
    Commented Feb 4, 2023 at 16:41
  • \$\begingroup\$ Welcome! Resistors with very low tempco and drift are widely available. Your differential measurement and 10 bit resolution will be the bottleneck. Have you looked into commercial offerings since your application isn’t new so no need to reinvent the wheel. \$\endgroup\$
    – winny
    Commented Feb 4, 2023 at 16:41
  • \$\begingroup\$ Yes, I have just looked it up and there are many current sensors which seem quite accurate. Thanks! \$\endgroup\$
    – Karim
    Commented Feb 4, 2023 at 16:50
  • 1
    \$\begingroup\$ Post a schematic. If you're using a small resistance in a place where the common-mode voltage varies a lot, then the actual current signal may well get swamped out in the lack of resolution in the DAC. Usually you want to (A) try to have the resistor go to ground, and (B) do some analog processing on it before it gets converted. \$\endgroup\$
    – TimWescott
    Commented Feb 4, 2023 at 17:12
  • 1
    \$\begingroup\$ Edit your question by including a schematic, that is. \$\endgroup\$
    – TimWescott
    Commented Feb 4, 2023 at 17:16

1 Answer 1

0
\$\begingroup\$

If the armature and field are in series as are many brush motors you can simply the total current the motor is drawing.

You can purchase a decent current shunt from your favorite china supplier for a few dollars US. You can even get them with a digital meter from ebay for less than $10 US. "dc current meter w/ shunt" was my search term.With the shunt you can insert it in your motor circuit where you like.

\$\endgroup\$
2
  • \$\begingroup\$ This is very helpful and I this is how I will attempt to do it. I will not mark it as a correct answer however, as i feel i am not qualified enough to know if there would be a complication for whatever reason. Thanks for your input! \$\endgroup\$
    – Karim
    Commented Feb 6, 2023 at 8:01
  • \$\begingroup\$ Only you can mark it as an answer. I am glad it helped. \$\endgroup\$
    – Gil
    Commented Feb 6, 2023 at 20:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.