How to Measure the Current of a Normal 12 V DC Motor?

DRV8838x data sheet...

https://forum.allaboutcircuits.com/threads/current-limiting-for-a-dc-motor.126217/

https://www.pololu.com/product/2511

"NORMAL" leaves a lot of room for speculation.???

Here is a link to some experts on the Arduino:

There are lots of people there that can help you design the system you are working on.

https://www.etechnophiles.com/category/projects/electronics/arduino/

<...if the motor is about to stall...> then it is undersized.

Google "current trips".

The easy way to measure current is to measure voltage across a series resistor.

Choose the resistor to be as large as possible given that you don't want it to take too much power from the motor. It needs to be large because it needs a very large capacitor in parallel with it to smooth out the wrinkles caused by the motor "gulping" current. The RC constant of the parallel combination needs to be greater than the length of the longest expected gulps.

Feed the voltages from "top" and "bottom" of the resistor into a differential amplifier, and, feed the output of the amp into a comparator. Set the other input to the comparator at the voltage which matches the trip current required. Use the output of the comparator to control the enable pin on the driver.

There, all

Can I put a very low ohm resistor in series with the motor power feed and measure the voltage drop across it? So that I can calculate the current through the voltage and the resistance.

https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor

<...Can I...> CR4 is not a permission-giving entity.

Yes, look up dc motor shunt, which is a very low resistance that is calibrated to produce a millivolt signal. This is a very old technology, but will require isolation from your dc motor voltage. You may find that a Hall Effect transducer may be economic, if it comes with an output that connects directly to your controller, as Redfred notes in Thread #10.

Consider the value of adding a temperature sensor and a trip circuit into the setup.

Yes, there are multiple easy ways (for me) to measure the current draw of a DC motor.

First, I think a quick refresher on DC motors is merited. Many brushless DC motors have self contained circuitry and sensors to handle commutation switching.

The two most popular methods to measure DC current use either a Hall effect sensor or a fixed current shunt (resistance) and ancillary circuitry to measure the differential voltage.

It is possible to buy a shunt resistance, available from 2 to a hundred amps, and a meter readout that gives both voltage and current displays and some even have a voltage output related to the current which can be used as an input to the package.

I have used a Picaxe chip to do the same thing to control the current in a welder.

If you are trying to avoid motor stall you could monitor motor speed by looking at the back EMF. Use your pwm signal to look at the motor voltage while the drive is off. A simple comparator circuit would let you shut the motor down when it's speed falls below a set threshold.

PWM-based motor controllers often have built-in overcurrent protection.

The DRV8838, which is used here, has overcurrent protection set at 1.8 A, not adjustable. The old LM298 had overcurrent protection that you could set with external resistors.

You could also use the overcurrent sense pins to measure the motor current since they are the ground for the h-bridge.

All the Original Poster has to do is determine at what current the trip should happen, and design accordingly. It's not something the forum can do, frankly.