Debug & Analysis of IoT Power Requirements

Battery life is an operating-profile problem, not a single current reading. A connected device can spend most of its time in microamp sleep, wake for milliseconds, draw a large radio burst and return to sleep. A useful measurement therefore has to capture peak current, charge per event, time in each state and the frequency of those states.

Turn the user requirement into a power budget

Choose the measurement method

A DMM is useful for stable current and long-duration average measurements. An oscilloscope across a current-sense resistor captures fast state changes. A current probe avoids inserting a shunt but may not provide the sensitivity needed for very low sleep current. Many projects need more than one method because the dynamic range between sleep and transmit is too large for one setup.

For a shunt measurement, calculate burden voltage at the highest current and signal level at the lowest current before choosing the resistor.

A practical test sequence

• Define representative customer use cases and the required runtime.
• Measure true shutdown and each sleep state with peripherals configured as shipped.
• Capture cold boot, warm boot and wake-up sequences.
• Measure sensor, storage, display and communications events separately.
• Integrate current over each event and multiply by its measured occurrence rate.
• Run a long capture to find retries, timeouts and unexpected wake-ups.
• Repeat after firmware changes and retain the same supply, probes, shunt and trigger conditions.

Common errors

Recommended instruments