5. Host software#
The Joulescope host software runs on a host computer and communicates with the Joulescope instrument over USB 2.0 high-speed.
The software works with Microsoft® Windows®, Apple® macOS®, and Linux®. See the supported platforms.
5.1. Installation#
Follow Installing the Joulescope UI.
5.2. Multimeter view#
Upon launching the host software, you see the multimeter view:
You can return to this view at any time using View → Multimeter.
The multimeter view provides the present operating state at a glance. The multimeter view displays several quantities:
Electrical current in amperes (A)
Electrical voltage in volts (V)
Power in watts (W)
Energy in joules (J)
Charge in either coulombs (C) or amp-hours (Ah).
This display, along with all other value displays in the Joulescope software, the SI standard prefixes for orders of magnitude:
Prefix |
Power |
Name |
|---|---|---|
G |
10⁹ |
giga- |
M |
10⁶ |
mega- |
k |
10³ |
kilo- |
m |
10⁻³ |
milli- |
µ |
10⁻⁶ |
micro- |
n |
10⁻⁹ |
nano- |
p |
10⁻¹² |
pico- |
The multimeter view updates every half second (0.5 seconds) by default. The software computes and displays the statistics over each half-second time window. The large numbers are the mean (also called average) value of that quantity over the window. The software also displays:
σ: The standard deviation
min: The minimum value
max: The maximum value
p2p: The peak-to-peak value, which is equal to (max – min)
Note that energy does not display these additional statistics since they are not meaningful.
Every update represents only the data recorded over the last half-second. If you click on the “Accumulate” button to activate it, then the software extends the statistics to combine each new half-second window without discarding results from previous windows.
5.3. Oscilloscope view#
The software includes an oscilloscope view. Click View → Oscilloscope.
The first view allows you to control the connected Joulescope. Press
to pause or resume capturing live data. Press
to start and stop recording data to a file. This
feature is only available when the device is capturing live data.
Current Range allows you to select Joulescope’s active shunt resistor. Most applications use auto, where Joulescope automatically selects the best range. However, you can manually force the range. Select off to disconnect power to the target device.
Voltage Range allows you to select the voltage range. Joulescope includes a 15V range and a more sensitive 5V range.
The Control widget in the Oscilloscope view also displays the energy or current consumed. Left-click or select Tools → Clear Accumulators to reset the accumulators to zero. Right-click or use File → Preferences → Units → Accumulator to set the displayed field to either energy or current.
The software displays two different waveforms by default. The top waveform is electrical current, and the bottom waveform is electrical voltage. The x-axis is time. If you have a Joulescope connected, it will automatically add the most recent data to the right of the waveform and shift existing data to the left. The y-axis data is the value measured at the corresponding point in time. Joulescope captures data 2 million times per second. When zoomed out, each x-axis pixel may represent many, many samples, which are that pixel’s sample window. The plot displays the statistics over each pixel. The yellow line is the mean (average). The red lines are the minimum and maximum. Power glitches, such as interrupt service routines, are very interesting for energy optimization. The minimum and maximum ensure that you do not miss these events, even when zoomed out. When you eventually zoom in far enough, the red lines disappear because 1 pixel becomes 1 sample, and the minimum and the maximum are the same as the average. You can use File → Preferences → Waveform → show_min_max to disable these lines or display the minimum to maximum region as a fill instead.
The software computes statistics quantities over the full-time window shown in the present view for each waveform. The software displays the statistics on the right edge of the window. The statistical quantities are:
µ: The mean (also called average) value
σ: The standard deviation
p2p: The peak-to-peak value (max - min)
min: The minimum value
max: The maximum value
∫: The integral over the time window
The waveform view supports Annotations to present additional information, which includes:
A Single Marker that displays information at a single point. Names used by other equipment for this feature include marker and cursor.
Dual Markers that display information over a time window. Names used by other equipment for this feature include cursors, timing markers, window, and range selection.
To display statistics at a single point, move the mouse to the x-axis time labels near the top. Then right-click (control-click on Mac OS) to bring up the context menu. Select Annotations → Single Marker.
Left-click the marker to move it with the mouse. As you move the mouse over the waveforms, the vertical marker follows along. The line displays statistics about that location:
t: The sample time for the displayed sample or window
µ: The mean (also called average) value
When the location contains more than one sample per displayed pixel, the line displays statistics over that single pixel’s sample window:
σ: The standard deviation
p2p: The peak-to-peak value (max - min)
min: The minimum value
max: The maximum value
Left-click again to keep the marker in position.
To display statistics over a selectable range, right-click on the x-axis time labels and select Annotations → Dual Markers. Left-click a marker to move it with the mouse, then left-click again to stop moving the marker. Hold the Ctrl key while left-clicking to move both markers together. Right-click (control-click on Mac OS) on one of the dual markers to export data or perform analysis over the selected range.
Use the scroll wheel to zoom in and zoom out. The zoom operation keeps the point under the mouse cursor at the same location after the zoom operation. However, when you reach the maximum extents while zooming out, that point may move. When viewing live data, the zoom operation always keeps the most recent data in view at the right.
Press the left mouse button and drag the cursor left or right to pan in time. Pan is not supported when viewing live data from a Joulescope.
The software displays the waveform on a linear scale with automatic y-axis ranging by default. The y-axis context menu has additional options. Right-click (control-click on Mac OS) on the y-axis to display the menu.
When manual ranging is activated, hover over the y-axis and use the scroll wheel to zoom in and out. Left-click and drag up and down to pan the y-axis.
Use the y-axis context menu to change the y-axis scale mode. The y-axis displays in linear coordinates by default but also supports a logarithmic scale. A logarithmic scale is handy to view wide dynamic ranges for current and power.
Use the y-axis context menu to hide the signal. Click Settings at the top left to display the settings menu. Select Add → [Signal Name] to display a signal not already shown.
5.4. Energy and Charge#
The Joulescope measures current and voltage two million times per second. It then multiplies current by voltage to compute power. Joulescope then integrates power over time to compute energy. It also integrates current to compute charge. Joulescope displays energy in both the Multimeter view and Oscilloscope view. This value starts accumulating when the software starts. Use Tools → Clear Energy to reset it to zero at any time.
The energy value and charge value provide a simple measurement to observe changes, especially for software. You can baseline the performance of an operation by recording the measured energy or charge value. You can then make changes, repeat the test, and observe the new energy or charge value. The oscilloscope view enables you to investigate in further detail.
5.5. Open-source#
The host software is open source and written in Python (supported platforms). The host software consists of two layers:
Repo name |
Python package name |
Description |
|---|---|---|
pyjoulescope_ui |
joulescope_ui |
The Joulescope User Interface written in QT/PySide2 |
pyjoulescope |
joulescope |
The Joulescope “driver” which enables scripting |
The joulescope package was designed so that you can script custom Joulescope actions and integrate Joulescope into your applications.
See the GitHub repositories for the latest details.
You can find examples for how to use Joulescope in your Python application at:
jetperch/pyjoulescope_examples
Also see the pyjoulescope documentation.
The Joulescope software depends upon other software and libraries. See CREDITS.html for pyjoulescope_ui and pyjoulescope.