Joulescope JS110: Precision DC Energy Analyzer

[mliberty]

Hi All!

The Joulescope JS110 Precision DC Energy Analyzer launched today on Kickstarter. (Full disclosure - I created this instrument!)



Joulescope is the most affordable and easy-to-use tool that enables you to create better, more energy efficient products.  Joulescope measures current and voltage, then computes power and energy.  A few features set Joulescope apart:

• Dynamic range: 10 amps down nanoamp resolution
• Low voltage drop: 25 mV @ 1A (20 mV max across shunt resistor up to 2A)
• Great bandwidth: 250 kHz bandwidth with 2 MSPS
• Easy to use: Simple multimeter view and more detailed oscilloscope view with waveforms over time
• Customizable: Host software is open source.  Swappable front panel is also open source!
• Portable: Light and small - can travel.
• Affordable: $499 on Kickstarter ($449 early bird) with $799 retail (USD).

You can download the User's Manual.

You can think of Joulescope as a very fast auto-ranging version of µCurrent combined with a voltmeter, 2-channel isolated 14-bit scope and open-source software for your computer.

Here's a high-level block diagram:



I sent one to mailbag, and I know that it arrived a couple weeks ago.  Let's hope that Dave gets around to checking it out soon!


Let me know what you think about the features, and hopefully the teardown when we see it.  If you're interested, check out the Kickstarter!

[lucazader]

Very interested in this.
Have been looking for a good solution that has higher dynamic range than the uCurrent.
We have a battery operated device that controls a motor, So we often see peak currents ~3A or so, but only briefly. And then we need to see the idle and sleep currents of the uC's.
Just need to convince the boss that we need this now!

Definitely would be awesome if dave has a look into this!

[mliberty]

@lucazader That's a great application for Joulescope!  I'm happy to answer any questions you may have!

[lucazader]

I See that the front panel with the banana connectors is opens source and swap-able.
This is great for designing our own more convenient connectors.

However, will you be designing and selling alternate front panels?
Eg: A USB-C in and out panel? Would be great for measuring charging/discharging current of devices.

[mliberty]

I do plan to design and sell some front panel variations.  I already have USB 2.0 and BNC.  I can easily add binding post and terminal block.  For the Kickstarter, I will see what backers want as I described in the FAQ. 

A USB-C front panel with only high speed support would not be too difficult, but I am not sure about SuperSpeed.  It could probably work but it would need carefully controlled impedance and routing.  For the application you have in mind, do you need SuperSpeed, or just high speed with USB Power Delivery?

[2N3055]

Don't make specialist front panels. Make adapters.
You need to optimize product and manufacturing to be able to actually deliver good product on time.
Adapters for few 10s of euros are additional product, good for customer (buy instrument and then adapters they need, if any) and to you it is additional source of income, albeit small.
And them make kits , just instrument, instrument with adapters for this and that and deluxe kit with many adapters.
For special purposes people can make their own..

[jeremy]

I’m in for an early bird. You got me at “open source host software”. I just hope that the plan is to maintain the software, and not to rely on community maintenance.

Frankly, I was planning on designing a product like this myself, but now you’ve saved me the hassle! If you need an extra beta tester, please let me know as I would be very keen; I am constantly measuring and testing devices going between full RF transmit and ~10uA sleep mode.

[lucazader]

@2N3055
Thats exactly what the front panels are: adaptor boards to the internal connectors.
I expect commonly used front panaels such as the includedbanana plugs, and mentioned BNC and binding posts and probably some usb ones the a lot of people would use would be a good idea for jetperch to offer.
But great that the front panel will be open source so anyone can make their own version for in-house testing with non commonly used connectors.

@mliberty
Yea I would suspect HS would be fine for most applications (at least mine), but Maybe would be better to poll the community.
Something to help monitor current with USB-PD would be great, as going through a standard USB 2.0 port you would loose PD.

However I can definitely wait for more boards to be brought out over time as interest picks up for a certain connector or format.
Just good to know that you are planning to make them going forward!

[mliberty]

@jeremy Excellent & thanks!  I do plan on developing and maintaining the host software.  I would love to get community engagement & contributions, but I plan to lead either way.
Thanks for the beta tester offer.  I'm out of units now but should get some back in the not too distant future.

@2N3055 & @lucazader
Ignoring terminology, I think that the focus is on creating simple ways that allow people to connect their stuff up to Joulescope.  I call this a "front panel".  The reason I decided not to use only external adapters is that they introduce yet more voltage drop and add more parasitics that reduce bandwidth.  I have attached a picture of the three existing front panels so that you can see how simple they are.  The front panel is just a PCB, connectors and a press-fit light pipe.  A new front panel would make a great first PCB design project!  You are right that I don't want to get distracted with lots of front panel designs for the Kickstarter.  The USB A/B is very popular with people using the beta units since it works with most development boards while allowing USB/UART programming and power monitoring.  Think Raspberry Pi, Arduino, ESP32, and more.

@lucazader
USB-C with PD (no SuperSpeed) should be easy to design, just like my existing USB A/B front-panel adapter but with the two PD signals.

[luma]

How would you compare this against existing instruments like the Qoitech Otii which offer similar features and (in this case) a license upgrade for battery simulation.

[mliberty]

Hi @luma,

You can check out the Joulescope User's Guide, available here, which you can compare against the Otii features URL you referenced.  Joulescope is a test measurement instrument only.  Otii includes a power supply and electronic load so that it can do battery simulation.  Otherwise, the performance specifications are not even close.  For example, Joulescope has 250,000 Hz analog bandwidth while Otii has 400.  Even RTOS ticks are typically 1 kHz.  I hope that I get a third party to do a proper comparison.  Are you interested?

[2N3055]

Thank you for clarification, that is in line of my thinking.
I would still call it "front panel adaptor" for less confusion.

[mliberty]

@2N3055 Yeah, naming things is hard.  Sorry for the confusion!

[mliberty]

@BitWrangler1001 asked in this thread to see the Joulescope step response in much closer detail.  I am replying here since it seems to be a more appropriate topic for this response.

I used a custom load board as the Joulescope target.  The load board was specifically designed for the sole purpose of creating very fast, repeatable edges.  It has a 1 MΩ resistor in parallel with a 1Ω resistor.  The board contains a momentary pushbutton and debouncer which is the input to the MCP1416 MOSFET driver.  The MCP1416 drives the FDMC7678 MOSFET which enables or disables the 1Ω resistor.  The entire circuit is powered by a 9V battery and connected to the Joulescope OUT.

I used a Siglent SPD3303X-E bench supply configured for 1.00V and 2.9A.  The supply is connected to Joulescope IN.  Any bench supply with reasonable transient performance should do.

I have attached a picture of the setup.

I then used the normal Joulescope software to capture data while pressing the target board's switch to toggle the MOSFET & 1Ω resistor.  I created a Python script to read the data, process the data, and create plots.  The python script finds each edge and aligns them so that they can be plotted together.  The plots show rising edges in the left column and falling edges in the right column. 

The first capture "step_2A.png" is the baseline with Joulescope autoranging disabled and set to a fixed 2A range.  The rise time you see is due to the Joulescope bandwidth.  The actual edge is much, much faster. 

The second capture "step_autorange.png" is with autoranging.  The two samples after over-range tend to contain "garbage" data that messes up the y-axis range, so I have omitted them.  These samples are captured at 2 MSPS (500 ns).  Joulescope's stated bandwidth is 250 kHz (4 µs = 8 samples). 

The Joulescope specification says that range switching occurs within 1.2 µs max.  This spec determines how much (or in the case of Joulescope, how little) voltage drop happens when the target changes current demands.  The Joulescope specification gives over-range settling time is 1.5 µs typical with 3 µs max.  This specification determines how well Joulescope can measure data through the transition.  Any autoranging ammeter needs to be VERY fast to limit voltage variations at the target device, and Joulescope was designed to meet these demanding requirements.

Comments?

[mliberty]

How do you synchronize Joulescope with your microprocessor and other test equipment?  A number of backers and beta users have asked this question, and we have an answer!  The production Joulescope will include 2 general purpose inputs (GPI) and 2 general purpose outputs (GPO).  You can read more in the Joulescope Kickstarter campaign updates:
Update #2: New Joulescope Feature
Update #5: GPI/O Feature Update

The Kapton tape that you may have seen on the beta units will also not be needed for the production units.  The production unit PCB design will have the proper 1 mm clearance from the enclosure to maintain sensor isolation.

[mliberty]

Attached is a rendering of the new Joulescope rev E PCB which includes the new GPI/O feature (top right 2x3 connector) and edge rails.  The edge rails with 1 mm clearance to the sensor side eliminate the need for the Kapton tape.  The prototype rev E boards are in fab at OSH Park now, and should be ready by Feb 25.  The Joulescope Kickstarter is 123% funded with 9 days remaining!

[SilverSolder]

Does the impedance / burden voltage of the Joulescope change when it auto-switches range?

[mliberty]

Does the impedance / burden voltage of the Joulescope change when it auto-switches range?

Joulescope normally performs shunt resistor autoranging to achieve its very high dynamic range.  Joulescope switches ranges (shunt resistor values) to keep the total burden voltage over the shunt resistor below 20 mV.  The User's Guide (download) contains more detailed information.  I have also attached the table below as an image.  You can manually set Joulescope to a fixed current range if desired.

[EEVblog]

I sent one to mailbag, and I know that it arrived a couple weeks ago.  Let's hope that Dave gets around to checking it out soon!

I have shot the video opening it but have not played with it. This weeks mailbag contained a few items that need setup and experimenting with, so it's taking longer than usual.

[LapTop006]

I sent one to mailbag, and I know that it arrived a couple weeks ago.  Let's hope that Dave gets around to checking it out soon!

I have shot the video opening it but have not played with it. This weeks mailbag contained a few items that need setup and experimenting with, so it's taking longer than usual.

... and now a whole lot longer.

[mliberty]

The most recent EEVblog mailbag included Joulescope!  If you filter Dave's frequent rants about software, I think he was impressed with Joulescope, even if he can't recommend it for competitive reasons.  I explained in the video comment (which Dave was nice enough to pin) how to use the software and how it will be improving. I am happy to address any questions.

Optimizing energy consumption and maximizing battery life has never been easier or more affordable.  Back the Joulescope Kickstarter campaign and be one of the first to own this great new instrument.  But be quick to get Joulescope at $499, a $300 discount off the future retail price.  The campaign is fully funded and ends on Thursday, March 21 at 9 am EDT (1 pm UTC)  -- that's only hours from now!

[drescherjm]

I am interested in the reason for the delay that Dave saw in the review. Is it processing speed of the PC? Buffering? Software needs optimized? Or some other reason?

[Kean]

I am interested in the reason for the delay that Dave saw in the review. Is it processing speed of the PC? Buffering? Software needs optimized? Or some other reason?

There is some info on this in the response from Joulescope on the video (edit: removed the YT comment link as it just sticks in a preview)

The Joulescope oscilloscope display allows you to pan around in time, which explains the delay you were seeing. The buffer is 30 seconds long by default, and the "present" time is at 30 seconds. Although this is useful for some applications, I will add a new option enabled by default that will follow the "present" view. That way, you will not get "behind time" and will always see present data.

[mliberty]

I am interested in the reason for the delay that Dave saw in the review. Is it processing speed of the PC? Buffering? Software needs optimized? Or some other reason?

The existing Joulescope software maintains a fixed length RAM circular buffer on your computer which is 30 seconds by default.  This buffer allows you to pause the recording and pan & zoom to older data -- a very good thing.  When you press play, the existing software keeps this offset from the present time.  If Dave had used the controls to pan to the right, he would have eventually "caught up to" present time.  My son gives a good demonstration of the very small actual delay in the full Joulescope software in this YouTube video.

While there are some uses for keeping the offset, it is confusing to some who think Joulescope is just an oscilloscope.  I will be adding a feature enabled by default that will return the view to zero time offset when you press play.

Dave's other main confusion was also related to the assumption that Joulescope is a traditional triggered, fixed memory oscilloscope.  Joulescope data sampling is always-on at 2 MSPS.  Every sample gets transferred to the host computer.
 After (or even while) you collect data at full rate, you can pan & zoom in the User Interface to explore features of interest at up to the full 2 MSPS.  Traditional oscilloscopes with limited memory buffers typically sacrifice time resolution when you are zoomed out in time.  Joulescope keeps full time resolution even when zoomed out.  The max/min lines help you find areas of interest that may otherwise be hidden due to the zoomed out timescale.