In some applications, it is important to add some kínd of circuit to monitor the current drained by a motor. This circuit can be used to control the speed or to manage the use of power, extending the battery life. Figure 1 shows how this circuit can be added.
Figure 1 – Typical current sensing using a resistor
A resistor of 0.1 ohm causes a voltage drop of 100 mV for each ampere drained by a motor. Adding an operational amplifier with gain 10, for instance, you will have 1 V/A directly driving some control circuit or monitor Circuit. The value of this resistor must be as low as possible so we dont “steal” energy from the motor.
