Power Measurement & Instrumentation on Embedded Systems Development

Current Sensing Methods

Mon, 01 Jan 0001 00:00:00 +0000

Current Sensing Methods#

Every power measurement begins with converting a current into a voltage that can be digitized. The dominant technique in embedded systems is the shunt resistor — a low-value, precision resistor placed in the current path so that the voltage drop across it is proportional to the current flowing through it. The fundamental relationship is Ohm’s law: V = I × R. A 100mA current through a 100mΩ shunt produces a 10mV signal. The entire accuracy of the measurement chain depends on the shunt resistor value, its tolerance, its placement on the board, and how the resulting voltage is amplified and digitized.

High-Side vs Low-Side Sensing

Mon, 01 Jan 0001 00:00:00 +0000

High-Side vs Low-Side Sensing#

The shunt resistor must go somewhere in the current path — either between the supply and the load (high-side) or between the load and ground (low-side). This choice determines the common-mode voltage the measurement circuit must handle, the complexity of the amplifier, and whether the load’s ground connection remains undisturbed. Both topologies are widely used, and each has distinct advantages and failure modes.

Low-Side Sensing#

In low-side sensing, the shunt resistor sits between the load’s ground return and the system ground plane. The voltage across the shunt is referenced to ground, making it straightforward to measure with a ground-referenced op-amp or a single-ended ADC input.

Power Analyzer Tools

Mon, 01 Jan 0001 00:00:00 +0000

Power Analyzer Tools#

Measuring embedded power consumption requires instruments that can capture both the microamp sleep currents and the hundred-milliamp active bursts that characterize modern low-power firmware. A standard benchtop DMM, sampling at a few readings per second, averages out the brief transmit bursts and deep-sleep intervals — reporting a single number that represents neither the peak nor the baseline. Dedicated power analyzers solve this by combining high-speed sampling with wide dynamic range, continuous capture, and software tools for analyzing energy over time.

In-Circuit Current Monitoring

Mon, 01 Jan 0001 00:00:00 +0000

In-Circuit Current Monitoring#

External power analyzers provide detailed captures during development, but many applications need continuous current and power measurement in the deployed product — battery fuel gauging, over-current protection, load profiling, and energy budgeting across subsystems. The INA219 and INA226 from Texas Instruments are the standard I2C-based current and power monitors for this purpose. Each integrates a programmable-gain ADC, a multiplexer for shunt and bus voltage, and on-chip calibration and power calculation registers, providing milliwatt-resolution power data through a two-wire bus with no external amplifier.