2.1 Current Measurement

Current cannot be directly measured using an ADC. Since an ADC measures voltage, and according to Ohm’s law, the result must be divided by the resistance of the circuit to reflect the current. The current can easily be calculated for a circuit with a constant and known resistance, for example, a simple LED in series with a resistor. However, the circuit resistance is often neither constant nor know in a more complex application.

For systems with variable resistance, a resistor can be added in series with the circuit to be measured. All the current passing through the circuit also passes through the resistor. Therefore, the current may be calculated based on the voltage across it and its resistance value. Usually, this resistor is called a shunt resistor, R_SHUNT.