Joulescope JS220 User manual
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Joulescope™JS220 User’s Guide
Precision DC Energy Analyzer
Revision 1.3
Last revised 2022 October 25
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1. Affordable, easy-to-use, accurate and precise
Multimeter view
Oscilloscope view
Applications include:
•Microprocessor and microcontroller power profiling and optimization
•Hardware power optimization
•Microcontroller and device sleep current optimization
•Hardware and software troubleshooting
•Software characterization and interrupt service routine profiling
•USB inrush and suspend current pre-compliance testing
•General-purpose current, voltage, power, charge, and energy measurement
The Joulescope™JS220 is the most affordable and easy-to-use precision DC energy analyzer. It
measures current and voltage, then computes power and energy. Many modern battery-powered
devices and IoT devices have a high dynamic current range, which makes accurate measurement
difficult. When “sleeping” the devices consume nanoamps (nA) or microamps (µA), but when active,
they consume milliamps (mA) or amps (A). Joulescope combines high-speed sampling and rapid
dynamic current range switching to provide accurate and seamless current and energy measurements,
even for devices with rapidly varying current consumption. The unprecedented accuracy and low-cost
of Joulescope allows every engineer on the team to measure the energy consumed by the target device
during development. Joulescope provides rapid feedback on how changes affect the overall product
battery life.
Joulescope displays instantaneous voltage, current, power, and energy, like a multimeter. The
multimeter provides a quick and easy summary of the present state of your device.
Joulescope displays waveforms of voltage and current over time, like an oscilloscope. This oscilloscope
view allows you to identify and to troubleshoot dynamic behavior and short events, including inrush
current, event handlers, and tasks.
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2. Key benefits
•Dynamic range: The Joulescope JS220 accurately measures electrical current over ten orders of
magnitude from amps down to nanoamps. This wide range allows accurate and precise current
measurements for modern devices. Sleep modes are often just nanoamps (nA) or microamps
(µA). Active modes are often milliamps (mA) or amps (A).
•Low voltage drop: Most multimeters and current meters have a significant voltage drop
(sometimes called burden voltage or insertion loss), which affects the actual voltage delivered to
the device under test. Joulescope has a total voltage drop of 25 mV at 1 A, which keeps your
target device running correctly. Joulescope’s extremely fast current range switching maintains
low voltage drop even under rapidly varying current demands.
•Makes the invisible visible:The JS220 measures current and voltage 2 million times per second
with 300 kHz bandwidth. This high sampling rate makes the power consumption of interrupt
service routines, inrush currents, and other short events visible.
•Easy to use:The JS220 reports cumulative energy and charge consumption along with real-time
current, voltage, and power. The multimeter view clearly shows the most recent value, while
the oscilloscope view allows you to explore changes over time. Much simpler and more
accurate than anything in its class!
•Customizable: The host software is open source on GitHub. You can also swap the banana jack
front panel with front panels that have other connector types. The front panels are open source
on GitHub.
•Portable: The JS220 fits in your backpack and only needs a small part of your desk. It provides
precision measurements in a portable, unintrusive form factor.
•Affordable: The Joulescope JS220 is affordable and priced so that every developer on the team
can have one at their desk. With such convenient access, Joulescopes allow developers to see
the impact of their changes on energy consumption immediately. Developers can make
informed choices to account for battery life during design. Eliminate power consumption
surprises during final product testing!
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3. Key features
•±15V voltage range
•±3A current range, continuous
•±10A current pulses (<10 ms, < 3A average per second)
•Down to 0.5 nA resolution, equivalent to 34-bits of dynamic range
•Synchronously measures voltage and current at 2 million samples per second, 16-bit
•300 kHz bandwidth
•Rapid 1 μs switching between shunt resistors
•Enwavify™technology for consistent, accurate measurements through current range changes
•Computes power, energy, and charge
•Operates with minimal voltage disturbance between Current + and Current –ports
•Up to ±48V common-mode voltage between USB ground and sensing ports
•4 general-purpose inputs and 2 general-purpose outputs
•1 BNC trigger configurable for either input or output
•Programmable on/off for power cycling the target device and measuring inrush currents
•USB 2.0 high-speed host connectivity with modern USB C connector
•Host software support for Microsoft® Windows®, Apple® macOS®, and Linux®
•Host software user interface provides real-time graphs of current, voltage, and power over time
•Python library and scripting provided
•Host software is open source and available on GitHub
•Swappable front panel with open-source designs on GitHub
•Firmware upgradable
See Section 7 for the full specifications.
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4. Table of contents
1. Affordable, easy-to-use, accurate and precise .....................................................................................2
2. Key benefits...........................................................................................................................................3
3. Key features ..........................................................................................................................................4
4. Table of contents ..................................................................................................................................5
5. Meet Your Joulescope JS220.................................................................................................................8
6. Quick start...........................................................................................................................................11
7. Specifications ......................................................................................................................................13
7.1. Absolute maximum ratings.........................................................................................................13
7.2. Mechanical..................................................................................................................................13
7.2.1. Instrument Only..................................................................................................................13
7.2.2. Complete product kit ..........................................................................................................13
7.3. Recommended operating conditions..........................................................................................14
7.4. Specification conditions..............................................................................................................14
7.5. Current measurement specifications..........................................................................................14
7.6. Voltage measurement specifications..........................................................................................14
7.7. General specifications.................................................................................................................15
7.8. Parasitic effects specifications....................................................................................................15
7.9. Software-controlled fuse specifications .....................................................................................15
7.10. General Purpose Inputs & Outputs.........................................................................................15
8. Host software......................................................................................................................................17
8.1. Installation ..................................................................................................................................17
8.1.1. Linux....................................................................................................................................17
8.1.2. Windows .............................................................................................................................17
8.1.3. macOS .................................................................................................................................17
8.2. Multimeter view .........................................................................................................................17
8.3. Oscilloscope view........................................................................................................................19
8.4. Energy and Charge......................................................................................................................22
8.5. Open-source................................................................................................................................22
9. How to Connect Your Joulescope .......................................................................................................24
9.1. Measure only current (ammeter) ...............................................................................................24
9.2. Measure only voltage (voltmeter) ..............................................................................................25
9.3. Measure power supply provided................................................................................................26
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9.4. Measure target device consumption..........................................................................................28
9.5. Measure subsystem consumption..............................................................................................29
10. Theory of operation........................................................................................................................31
10.1. Ammeter .................................................................................................................................31
10.2. Voltmeter................................................................................................................................32
10.3. Host Computer........................................................................................................................32
10.4. Power, Energy, Charge, and Statistics.....................................................................................32
10.5. High impedance / low leakage................................................................................................33
10.6. Electrical isolation...................................................................................................................33
11. How to swap the front panel ..........................................................................................................34
12. GPI & GPO .......................................................................................................................................35
13. Electrical Isolation...........................................................................................................................37
14. Typical Behavior..............................................................................................................................38
14.1. Step Response.........................................................................................................................38
15. Maintenance...................................................................................................................................39
15.1. Verification Procedure ............................................................................................................39
15.1.1. Preliminary operations........................................................................................................39
15.1.2. Voltage Validation Process..................................................................................................39
15.1.3. Current Validation Process..................................................................................................40
16. Compliance .....................................................................................................................................43
16.1. United States...........................................................................................................................43
16.1.1. FCC Compliance Statement.................................................................................................43
16.1.2. FCC Notice...........................................................................................................................43
16.2. Canada ....................................................................................................................................43
16.3. Europe.....................................................................................................................................43
16.4. Safety ......................................................................................................................................44
16.5. RoHS Directive 2011/65/EU, 2015/863/EU ............................................................................44
16.6. Country of origin .....................................................................................................................44
17. Warranty.........................................................................................................................................45
18. Intellectual Property .......................................................................................................................46
19. Contact............................................................................................................................................47
20. Glossary...........................................................................................................................................48
21. User’s guide information ................................................................................................................50
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21.1. Copyright notice......................................................................................................................50
21.2. Publisher .................................................................................................................................50
21.3. Warranty .................................................................................................................................50
21.4. Change log...............................................................................................................................51
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5. Meet Your Joulescope JS220
The JS220 arrives in a carry case:
Unzip the carry case to find the JS220 instrument and accessories:
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Your Joulescope JS220 purchase includes:
•Joulescope JS220 instrument with factory calibration
•Binding Post Front Panel, already installed
•5’ USB 2.0 A to C cable
•GPIO cable assembly
•2 mm Allen wrench, for optionally swapping the front panel
•Quick Start Guide
•Joulescope sticker
•Carry case
You will need to provide:
•A host computer running Microsoft® Windows® 11 or 10, Apple® macOS® 12 or 10.15, or Linux®.
Most computers manufactured within the last five years should work. The computer requires
an available USB 2.0 port, at least 500 MB of hard drive / solid state drive storage space, and 1
GB of available RAM.
•Suitable cable(s) to connect the Joulescope JS220’s binding posts to your system, often the
power source and device under test.
•For computers without USB A ports, a suitable USB cable or USB adapter.
•Optional BNC cable for connecting trigger to other equipment.
You need an internet connection to download the free software.
The front side of the JS220 has the connectors that connect to your system:
Your JS220 measures the voltage across the Voltage + and Voltage –binding posts. Your JS220 measures
the current flowing through the Current + to the Current –binding posts. If you have a power source
and target device, connect the positive side through the current binding posts. You can then connect
the voltage signals across either your power source or your target device. For more connection
examples, see Section 9.
The Sensor Status indicator is off when your JS220 is powered off or inactive. Flashing red indicates that
the instrument is ready but the current flow is not yet enabled. Solid green indicates that current
measurement is enabled.
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The backside of Joulescope has the host USB connector, status LED, GPIO connector, and trigger
connector:
Use the provided USB C to USB A cable to connect the USB host computer connector to your host
computer. If your computer only has USB C ports, use an adapter (not provided) or a USB C to USB C
cable (not provided).
The Controller Status indicator is off when the JS220 is not connected to the host computer, or the host
computer has not yet activated the JS220 over USB. Microsoft Windows computers activate devices
immediately when connected while macOS and Linux do not active the device until the Joulescope
software attempts to use the device. Solid blue indicates that the JS220 is activated. Solid green
indicates that the JS220 device is running normally.
The GPIO connector provides four general-purpose inputs and two general-purpose outputs. See
Section 12 for details.
The BNC Trigger connector provides either a Trigger Out or a Trigger In. This Trigger allows the JS220 to
synchronize data collection with other equipment.
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6. Quick start
Download the host software from http://www.joulescope.com/download. Follow the instructions on
the download page to install the software for your platform. Windows and macOS hosts just need you
to install the software. Linux hosts also typically require that you manually install a udev rule. See
section 8.1 for details.
Start the Joulescope host software.
Connect the Joulescope USB port to the host computer using the provided USB cable. The host software
will automatically detect the connected Joulescope and start displaying data.
To measure the current and charge, connect the Joulescope Current port inline between the positive
output from your power source and your target device under test. The maximum voltage between any
port Current +, Current -, Voltage +, and Voltage –should never exceed ±15V. All sensor ports are
electrically isolated from USB, but the voltage between any port and USB ground should never exceed
±48V.
To also measure voltage, power, and energy, connect the Joulescope Voltage ports across your power
source’s positive and negative connections. Alternatively, you can connect the Voltage port across your
target device’s positive and negative connections.
The Joulescope JS220 can be used in a variety of measurement configurations. For more common
connection scenarios, see Section 9.
Operate your device under test. The Joulescope host software starts in the Multimeter view by default.
Use the Multimeter view to measure the current, voltage, power, charge, and energy consumption.
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Dive into more detail with the oscilloscope view. Select View →Oscilloscope Default to display
waveforms of voltage, current, and power over time.
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7. Specifications
7.1. Absolute maximum ratings
Min
Max
Unit
USB voltage
-0.3
6
V
Max voltage applied between any port
Current +, Current -, Voltage +, Voltage -
-20
20
V
Max voltage to USB ground from any port
Current +, Current -, Voltage +, Voltage -
-48
48
V
Input current (powered, burst)
-10
10
A
Input current (powered, sustained)
-3
3
A
Input current (unpowered)
N/A (off)
N/A (off)
A
Storage temperature
-40
80
°C
Operating temperature
0
50
°C
Relative humidity (non-condensing)
0
95
%
Altitude from sea level
-100
2500
m
Max voltage applied to GPI relative to USB ground
-10
10
V
7.2. Mechanical
7.2.1. Instrument Only
Typical
Unit
Weight
190
grams
Width
99
mm
Length (including binding posts and BNC connector)
126
mm
Height
28
mm
7.2.2. Complete product kit
Typical
Unit
Weight
510
grams
Width
190
mm
Length
200
mm
Height
60
mm
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7.3. Recommended operating conditions
Test condition
Min
Typical
Max
Unit
Operating temperature
10
40
°C
USB supply voltage
4.5
5.0
5.5
V
USB supply current
500
mA
Voltage applied across
Voltage + and Voltage -
-14.5
14.5
V
Voltage applied across
Current + and Current -
Current range off
-15
15
V
Input current
continuous
-3
3
A
Input current pulse
< 50 milliseconds,
< 3A average
-10*
10*
A
Input current pulse
< 250 milliseconds
< 3A average
-5*
5*
A
* Suitable for handling inrush currents when connecting capacitive loads.
7.4. Specification conditions
Temperature
23 °C ± 10 °C
Humidity
20% to 80% RH, non-condensing
Calibration interval
1 year*
* Recommended to comply with industry-standard practices, but the Joulescope JS220 is designed not
to need recalibration.
7.5. Current measurement specifications
Range
Accuracy
Resolution
Impedance
Guaranteed
10 A*
±0.25% ±1.50 mA
175 µA
0.01 Ω
±9.7 A
180 mA
±0.25% ±150 µA
15 µA
0.11 Ω
±185 mA
18 mA
±0.25% ±15 µA
1.5 µA
1.11 Ω
±18.5 mA
1.8 mA
±0.25% ±1.5 µA
150 nA
11.1 Ω
±1.85 mA
180 µA
±0.25% ±150 nA
15 nA
111 Ω
±185 µA
18 µA
±0.25% ±30 nA
1.5 nA
1111 Ω
±18.5 µA
* Joulescope is designed for 3 A sustained. See the recommended operating conditions for maximum
durations for higher currents.
Test current measurement bandwidth by varying the effective load impedance. Due to load
capacitance, altering the source voltage is not a valid method of testing current bandwidth.
The JS220 is sensitive to RF radiation which induces real current in test setups. When tested with
EN61326-1 and 3 V RMS/m, the JS220 measured up to 10 µA (observed, not guaranteed) of current at
several frequencies. The exact frequency susceptibility varies with cable length and configuration.
7.6. Voltage measurement specifications
Range
Accuracy
Resolution
Guaranteed
15 V
±0.1% ±10 mV
1.2 mV
±14.5*
2V
±0.1% ±2 mV
180 µV
±1.98
* Beta units are limited to ±13.6 V.
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The JS220 is sensitive to RF radiation which induces real voltages in test setups. When tested with
EN61326-1 and 3 V RMS/m, the JS220 error increased by 10 mV (observed, not guaranteed) at several
frequencies. The exact frequency susceptibility varies with cable length and configuration.
7.7. General specifications
Test condition
Min
Typical
Max
Unit
Sampling frequency
25 °C
2000000
sps
Sampling frequency
25 °C
-25
25
ppm
Measurement bandwidth
- 3 dB
280
310
350
kHz
Front panel insertions
100
7.8. Parasitic effects specifications
Test condition
Min
Typical
Max
Unit
Current leakage (Voltage + to -)
25 °C, ±3.3V
2
nA
Current leakage (Voltage + to -)
25 °C, ±5V
2
nA
Current leakage (Voltage + to -)
25 °C, ±15V
3
nA
Shunt resistor voltage, max
-2 to 2 A, static
20
21
mV
Burden voltage (Current + to -)
1 A, banana jacks
0
25
35
mV
Burden voltage (Current + to -)
Shunt resistor, < ±2 A
±20
mV
Shunt switching time
Over-range
< 200 ns rise time
0
0.8
1.2
µs
Measurement gap following a
current range switch
0
µs
7.9. Software-controlled fuse specifications
Test condition
Min
Typical
Max
Unit
Current leakage (Current + to -)
25 °C, 3.3V
±5
nA
Current leakage (Current + to -)
25 °C, 5V
±7
nA
Current leakage (Current + to -)
25 °C, 15V
±28
±5000
nA
7.10. General Purpose Inputs & Outputs
Test condition
Min
Typical
Max
Unit
Internal 3.3V reference
3.135
3.3
3.465
V
External reference
Vref < (VUSB –0.5 V)
Vref -
0.1
Vref
Vref +
0.1
V
Input leakage per pin
25 °C
±10
nA
Input leakage per pin
±100
nA
Output voltage high
-100 μA
Vcco -
0.1
V
Output impedance
10 mA
45
50
80
Ω
GPI sample rate
2
MSPS
Continuous output current
Per pin
±50
mA
Total power dissipation
Over output impedance
0.25
W
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8. Host software
The Joulescope host software runs on a host computer and communicates with the Joulescope JS220
instrument over USB 2.0 high-speed.
The software works with Microsoft® Windows® 11 and 10, Apple® macOS® 12 and 10.15, and Linux®.
For Linux, only Ubuntu 22.04 LTS is officially supported. The Joulescope software only supports 64-bit
operating systems with 64-bit Python 3.8+.
8.1. Installation
The Joulescope software is available to download at
www.joulescope.com/download/
Click on the download link for your platform. For a list of all releases for all platforms, see
https://download.joulescope.com/joulescope_install/index.html
Follow the usual process to download and install the software following the on-screen directions.
Several operating systems may require additional steps, as noted below.
We recommend installing the Joulescope software on the native operating system, not under a virtual
machine, due to Joulescope’s demanding USB communication requirements.
8.1.1. Linux
Many Linux systems, including Ubuntu, use “udev” to manage devices and grant permissions. You will
need to install a udev rule that grants Joulescope hardware access to your account. Download and
follow the instructions in this file:
https://raw.githubusercontent.com/jetperch/pyjoulescope/main/99-joulescope.rules
8.1.2. Windows
Windows 10 and Windows 11 machines should install and run without any additional steps.
8.1.3. macOS
The macOS distribution is currently signed, but it is not distributed through the Apple Store. macOS may
indicate security warnings upon installation. If you receive a security warning, control-click the
Joulescope application, then select “open” to bypass these security warnings. You will need to repeat
the control-click, “open” process several times (usually twice) until macOS finally allows the Joulescope
software to launch. After granting this permission once, subsequent runs will start normally.
8.2. Multimeter view
Upon first launching the Joulescope user interface host software, you see the multimeter view:
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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 I 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
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•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.
8.3. 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 2V range. Most measurements can use the auto setting, which allows the JS220 to determine
the best 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
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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 display 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:
Table of contents
