Use a Joulescope inline with an external supply to measure current and voltage during a known firmware workload. Captures appear in the Monitor’s Power tab. Identify the model and serial number before measuring; JS110, JS220, and JS320 differ in ranges, sampling, and digital I/O.
Prepare
Connect Joulescope by USB, close competing applications, and complete Embedder’s requested dependency setup. JS320 requires Python 3.12 or newer and pyjoulescope_driver 2.3.4 or newer. Device firmware older than 1.1.3 is rejected on JS320.
Wire the current and voltage paths
Joulescope does not supply voltage. Connect it between an external supply and the target using the wiring for the installed model and front panel.
I+ and I- to target VDD, connect the voltage-sense terminals as required, and share the reference ground. In a two-wire setup, tie V+ to I+; for Kelvin sensing, sense voltage at the target.
Use the exact device limits. Enabling the DUT current path permits current from the external supply; it does not set a supply voltage. On JS320, resolve the cause of a tripped fuse before asking Embedder to clear it and re-enable that path.
Measure a workload
Specify the supply, settling period, workload, duration, and final current-path state. Use automatic current ranging unless a known workload needs a fixed range. In a hardware script, joulescope_measure() performs a bounded capture; one-shot captures are limited to 60 seconds.
When choosing ranges and sample rates, use the connected model’s supported settings:
- JS110: supports the 2 A current range and 5 V voltage range; host samples can reach 2 MS/s.
- JS220: uses a 10 A range instead of JS110’s 2 A range, supports 15 V or 2 V voltage ranges, and caps host output at 1 MS/s.
- JS320: supports 15 V or 2 V voltage ranges and a configurable autorange window. Its supported sample rates differ from the earlier models; ask for the accepted rates rather than reusing a JS110/JS220 rate.
These are measurement settings, not permission to exceed the device’s input ratings. Check the applied settings before comparing results.
Record a longer test
For a live view, open setup in the Monitor’s Power tab and choose Joulescope, then select the available current and voltage ranges. Press Start, use Pause / Resume as needed, and press Stop to finish and save a capture. The live view’s Sample rate controls statistics windows per second, separately from the raw acquisition sample rate. The DUT power control enables or disables the external supply’s current path.
Choose the result you need:
- Periodic statistics: request current, voltage, and power statistics at a defined interval. Reset charge and energy accumulators when starting a new workload. A single statistics read returns the latest statistics window, not an aggregate of the entire time spent waiting.
- Live samples: start a stream, read samples during the test, then stop it and save the result you need.
- Raw recording: record selected current, voltage, or power signals to a
.jls file, then stop the recording and open its result. JLS recordings support longer tests and offline inspection in Joulescope software.
Stop a live sample stream before starting a JLS recording. Record the workload, firmware revision, supply voltage, and settling period with the result so another run is comparable.
To revisit a completed recording, give its .jls path and ask Embedder to open it in Power. This view requires both current and voltage signals in the recording. Long recordings are summarized for display; retain the JLS file for full sample-level inspection.
Correlate digital activity
For digital markers, give the GPI pin and target logic voltage. JS110 supports configurable I/O voltage; JS220 uses its internal 3.3 V reference or an externally wired Vref. On JS320, choose internal 3.3 V or the external VREF connection explicitly; wire external VREF to the target’s logic supply when using it.
You can read GPI states, drive supported GPO pins, or measure between observed GPI edges. Specify a maximum duration and the final GPO state. The GPI-window measurement uses software polling and is suitable for longer state windows, not microsecond timing.
JS220 can decode two 8N1 UART streams while measuring power. JS110 and JS320 do not expose this UART helper.
The UART result contains bytes without timestamps aligned to current samples. Use it to confirm that markers arrived during a capture. To compare current by state, hold the target in each known state and measure settled intervals separately.
Update JS320 firmware
If a JS320 needs a firmware update, ask Embedder to prepare a dedicated hardware script using joulescope_firmware_update(). Stop measurements and disconnect the software session first, while leaving USB plugged in. Review and approve the update separately from a measurement; after it finishes, reconnect and verify the reported firmware version.
Set the sample rate before you start. The rate counts statistics windows per second, not raw ADC samples. Each live sample is one on-device window with mean, minimum, and maximum values.
- JS110 and JS220 serve the
1, 2, 5, 10, 20, 50, and 100 Hz ladder.
- JS320 serves
1 Hz through 10 kHz.
- The device rounds a request to a rate it can serve. The toolbar shows the applied rate when it differs from the request.
Pick the voltage range and current range in the Setup panel before starting. A JS320 exposes a minimum and maximum current-range window; a JS110 or JS220 selects a single current range.
See live power controls for pausing, recording, and stopping the stream.
Troubleshoot
- Zero current: verify the current path and external supply; check for a tripped JS320 fuse.
- Wrong voltage: check voltage-sense wiring and the selected measurement range.
- Range or sample rate rejected: use settings supported by that model.
- Device unavailable: close competing applications and complete setup; JS320 may require a Python, driver, or firmware update.
- Long capture fails: use statistics, streaming, or a JLS recording instead of a one-shot capture.
- Digital marker missing: verify the pin, ground, I/O reference, and signal duration.
See Combined workflows for relating power to firmware behavior. 
