An oscilloscope can be used to measure both the average current over a given time
interval and capture the current profile.
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Mount a 10 Ω resistor between the pins on P23.
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Connect an oscilloscope in differential mode or similar with two probes on the
pins of the P23 connector, as shown in the following figure.
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Calculate or plot the instantaneous current from the voltage drop across the 10
Ω resistor by taking the difference of the voltages measured on the two probes.
The voltage drop is proportional to the current. The 10 Ω resistor causes a 10
mV drop for each 1 mA drawn by the circuit being measured.
The plotted voltage drop can be used to calculate the current at a given point in
time. The current can then be averaged or integrated to analyze current and energy
consumption over a period.
Figure 1. Current measurement with an oscilloscope
The following actions can be taken to reduce noise:
- Use probes with 1x attenuation.
- Enable averaging mode to reduce random noise.
- Enable high resolution function if available.
A minimum of one sample every 5 µs is needed to accurately measure the average
current.