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Joulescope: Precision DC Energy Analyzer

作者:淘博工业设计整理发布 日期:2019-03-20 人气:100

About

Measuring energy consumption during product development is crucial, especially for battery powered and always-on devices.  However, measuring energy consumption accurately has been expensive, tedious or error-prone.

We've designed something better.  Meet Joulescope®!

Joulescope is the most affordable and easy-to-use precision DC energy analyzer.  It measures current and voltage, then computes power and energy. 

Joulescope displays instantaneous voltage, current, power and energy, like a multimeter:

And Joulescope displays waveforms of voltage, current, and power over time, like an oscilloscope: 

Oscilloscope ViewOscilloscope View

Joulescope enables you to see what your target device is doing in real-time so that you can create better, more energy efficient products.

What people are saying

Joulescope's precision and fast sample rate enabled me to discover unexpected processing, and I reduced my device's energy consumption by removing this unnecessary processing.  Joulescope is now a valuable part of my toolset for debugging and verifying designs.

- Frank Hunleth, VP Hardware Engineering, SmartRent Inc.

Joulescope helped me get my firmware to much lower power states faster.  Having the Joulescope’s multimeter and oscilloscope view open while developing low-power firmware is now an essential part of my workflow.

- Alvaro Prieto, Firmware/Hardware Engineer

While developing a library to conserve power in embedded devices, I needed a tool to prove its effectiveness. Joulescope was all I needed to easily and accurately record device power consumption and performance. It is now an indispensable part of my embedded projects.

- Chris Freeze, Software Engineer, DockYard Inc.

As seen on

How to use Joulescope

Connect Joulescope's USB port to your host computer.  

Connect the Joulescope IN to your power source.

Connect Joulescope OUT to your device under test.  

Run the open-source Joulescope software on your computer.

Measure, explore, innovate.

Why Joulescope?

Amazing dynamic range:  Joulescope accurately measures electrical current over 9 orders of magnitude from amps down to nanoamps. This wide range allows accurate and precise current measurement 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 effects 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:  Joulescope measures current and voltage 2 million times per second with 250 kHz bandwidth.  This high sampling rate makes the power consumption of interrupt service routines, inrush currents and other short events visible. 

Easy to use:  Joulescope reports cumulative energy 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 Joulescope 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.  We ❤ open source.

Portable: Joulescope fits in your backpack and only needs a small part of your desk.  Take Joulescope wherever you want to use it!

Affordable:  Joulescope is affordable and priced so that every developer on the team can have one at their desk.  With such convenient access, Joulescope empowers 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! 

How does Joulescope work?

Joulescope simultaneously measures current and voltage, and then computes power and energy.  Joulescope combines a voltmeter and a fast auto-range current shunt ammeter. 

Both the voltage and current are sampled 2 million times per second, and the sample data is sent to the computer.  As the current changes, the ammeter selects the optimal shunt resistor value.  The shunt value selection uses the ADC output, dedicated over-range comparators, and a unique algorithm that runs in an FPGA.

The sensor side of Joulescope is electrically isolated from the host computer.  This allows you to insert Joulescope into your test system without worrying about ground issues including ground loops and ground noise.   You don't need to worry about settings or affecting your target device.  Joulescope just works. 

Specifications

  • -1V to 15V voltage range

  • -1A to 3A current range, continuous

  • Up to 10A pulses (< 10 ms, < 3A average per second)

  • Down to 1.5 nA resolution, equivalent to 32-bits of dynamic range

  • Synchronously measures voltage and current at 2 million samples per second

  • 250 kHz bandwidth

  • Rapid 1 μs switching between shunt resistors for seamless dynamic current measurement

  • Computes power and total energy

  • Operates with minimal voltage disturbance between IN and OUT ports

  • Up to ±48V common mode voltage between USB ground and IN-, IN+, OUT+, and OUT-

  • Two general purpose inputs (GPI) and two general purpose outputs (GPO) for synchronizing Joulescope captures with your target device and other equipment

  • Programmable operational/off selection for power cycling the target device and measuring inrush currents

  • USB 2.0 high-speed host connectivity with full-rate data streaming

  • Host software support for Microsoft® Windows®, Apple® Mac® OS X® and Linux®

  • Host software provides real-time graphs of current, voltage, and power over time

  • Host software is open source and available on github

  • Swappable front panel with open source designs on github

  • Firmware upgradable

See the Joulescope User's Guide for more detail.

Why is Joulescope Different?

Compared to a multimeter: The classic low-cost approach to estimating total energy consumption is to use a normal multimeter.  If the voltage is changing, you need two multimeters, but if the voltage is constant, you just need one multimeter to measure current.  Since the device has multiple power states, you need to put the device into each state and measure the current for that state.  You then need a model of how long the device is in each state.  You multiply the state currents times their duration and add them all together to estimate total energy.  This approach is very tedious and error-prone.  What happens if you accidentally change something that drastically effects energy consumption while using this method?  Are you performing this energy test every day?  Hardly.  You usually don't find out for weeks or even months which is really bad for the project.

Compared to an oscilloscope: Another classic approach is to use an oscilloscope with a shunt resistor.  This approach is limited to the oscilloscope's dynamic range, often just 10 or 12 bits, which is not sufficient for modern devices.  Let's take an example device that has 1 A active current and 1 µA sleep current.  To measure sleep current to 5% accuracy requires 24-bits of dynamic range, way more than any oscilloscope.  Joulescope provides the equivalent of approximately 32-bits of dynamic range!  The oscilloscope approach also requires you to measure the voltage across the shunt resistor, and you often need to float your circuit, float your scope, or use a differential probe.  Each option has disadvantages.  Another option, customized current probes, are expensive and still lack the dynamic range. 

Compared to customized equipment: The major test vendors have expensive equipment that allow accurate measurement under these conditions.  This equipment is great, but is priced closer to a new car than a multimeter.  Even if it fits into your budget, it is usually shared by the team.  If equipment is not convenient, developers rarely use it.  Developers need quick, accurate and cost-effective energy consumption measurements so that they have immediate feedback on the consequences of their changes.

The Backstory

At multiple times during his career, Matt Liberty, the creator of Joulescope, has been frustrated trying to measure the energy consumption of products.  With the increase in IoT, AIoT and wearables products, accurately measuring energy consumption is even more critical.  Nearly two years ago, Matt got fed up and decided to solve the problem.  Matt set out to democratize energy measurement by developing an instrument with a comparable cost to a multimeter but with the capabilities of the customized high end equipment.  

The initial target was to support up to +12V systems and +3.8V lithium-ion batteries with currents up to 2A and sleep currents down to 1 μA.  In order to measuring meaningful changes of 1 μA sleep currents, an accuracy of at least 100 nA was needed.  Matt knew that this high dynamic range would be an engineering challenge.

We developed Joulescope using an iterative approach so that we could quickly refine the design.  The conflicting goals of low cost and high precision required careful engineering.  Over the course of development, we built 17 different prototype boards.

Prototypes!  The many iterations that refined Joulescope.Prototypes! The many iterations that refined Joulescope.

Each prototype allowed us to improve the Joulescope design and to develop a cost-effective yet accurate way to measure this wide range of currents.  Due to the demanding and cutting edge requirements, we built even more test boards to fully characterize Joulescope's performance, especially the 250 kHz bandwidth and transient response.  

Some custom test boards that supported Joulescope developmentSome custom test boards that supported Joulescope development

In January, we completed the Joulescope beta build of 25 units.  This build allowed us to test the manufacturing process and get Joulescope into the hands of reviewers and a few eager engineers. 

Joulescope beta build: 25 unitsJoulescope beta build: 25 units

After nearly two years of work, we now have a product that is easy-to-use, affordable and exceeds our original performance goals.  

Rewards

Joulescope is now ready to help you build more energy efficient products.  We need your support to raise money for the Joulescope manufacturing run.

The "Kickstarter Special" Joulescope reward includes a Joulescope for $499 USD, a $300 discount from the retail price.  Each Joulescope reward includes the Joulescope instrument, a 6' USB cable and a sticker.

Joulescope is designed to empower every member of the development team to improve energy consumption.  We are offering three different team rewards that contain multiple Joulescopes.  The "Team Pack x5" reward includes 5 Joulescopes at a reduced cost.   The "Team Pack x10" reward includes 10 Joulescopes at a reduced cost.  The "Sponsor" reward includes 10 Joulescopes with one day of on-site training by Joulescope's creator, Matt Liberty, so that your team gets maximum benefit from this new tool.

The "Thank You!" reward allows you to join the Joulescope community and the Kickstarter ride!  If you think Joulescope is awesome, but not for you, please back this reward.

All backers of any reward become a member of the Joulescope community.  Although Joulescope is already a capable product, we plan on adding more features before shipment.  As a member of the community, you can help direct the future of Joulescope by recommending and prioritizing features that are most valuable to you!

When do I get my Joulescope?

Your Joulescope will ship the end of June 2019.  We already have our manufacturing partner selected and Joulescope beta units in the field.  After the Kickstarter campaign completes, we will be busy ramping up production so we can ship your Joulescope.  

The Team

We have assembled a great team that has the experience and knowledge to successfully manufacture Joulescopes and get them to you.

Matt Liberty is the creator of Joulescope, and also the project lead and engineering lead. Matt is a hardware and software engineering consultant focused on creating high-quality embedded systems. Matt has over 20 years of experience creating and manufacturing products.  Over the last 8 years as a consultant at Jetperch LLC, Matt has developed a number of successful products for a range of companies.  Before Jetperch, Matt was a Director at Hillcrest Labs.  He is also renown for his earlier work on Hillcrest Lab's Freespace motion sensing where he was granted 27 US patents related to motion sensing technologies.  Matt was a speaker and adviser to the Embedded Systems Conference for several years.  Matt is based in Maryland, USA.

Custom Electronic Co. (CEC) is the Joulescope manufacturing partner.  CEC assembles the circuit boards, performs top-level assembly, programs the units, and calibrates each unit. CEC is conveniently located near Jetperch, and works in close collaboration with Jetperch to ensure manufacturing success.

Allied Component Works provides design for manufacturing reviews, feedback and process improvements to ensure that every Joulescope meets our exacting standards.

Joulescope would not be possible without OSH Park, OSH Stencil, PCBWay, MacroFab, Protolabs, Storey Store Media, McMaster-Carr, Mouser, and Digikey.  StickerMule makes our spiffy stickers.

Risks and challenges

We have a skilled and dedicated team that has successfully brought products to market. All hardware products, including Joulescope, have risk going into manufacturing. We have worked diligently to minimize these risks so that we get your Joulescope to you on time.

Development: 
The Joulescope shipping box and packaging still needs to be developed. This often neglected step delays many products. We have identified a partner and have started this process. We plan on keeping packaging simple to reduce risk.

Hardware: 
Joulescope beta units are already being used by actual people in the field, which drastically reduces the engineering risk. Although unlikely, an issue discovered during beta testing could require additional time to resolve, likely require a PCB respin, and delay manufacturing.

Compliance: 
We have not yet performed official CE, FCC or USB certification. Any unexpected issues raised during certification could require additional engineering which would delay manufacturing.

Software: 
The firmware & FPGA code in Joulescope is fully upgradable in the field. The host computer software is easily upgradable. The only potential software issue that would halt production would be in the custom bootloader on the USB microcontroller. We have already developed and tested this bootloader, so any critical errors are unlikely, but the possibility still exists.

Production: 
Products may prove to be too difficult, time-consuming, or costly to manufacture. To reduce this risk, we have already built the beta units with our selected contract manufacturer. However unlikely, unanticipated manufacturability challenges could arise during the production build which would delay production.

Supply chain: 
Component shortages, especially for MLCC capacitors, are a global concern now. Parts shortages and long lead times are common with components going in and out of stock every day. We have no control over this. We have designed Joulescope to accept standard components to allow substitutions. We will place parts on order immediately (and already have ordered a few critical components!), but delays in component availability could delay manufacturing.