Little Bee Current Probe

[Weston]

I have mentioned in some previous posts I am working on a (relatively) low cost DC capable current probe. Since then the project has been accepted by Crowd Supply and as of today it has a pre-launch page! https://www.crowdsupply.com/weston-braun/little-bee

I am still working on finalizing the final design for the crowd funded campaign, so I figured now would be a good time to post about it in case anyone has feedback.

The key specs are a bandwidth of DC-10MHz, a sensitivity of 0.25V/A and a maximum current of +/- 5A. It also can operate in a magnetic field mode, similar to the i-prober 520.

Feedback / commentary is welcome! I am hoping to launch the campaign in the next month or so. Right now I am in the process of finalizing the design and collecting price quotes for manufacturing. Final sales price should be between $100 and $200 USD.
 

[PlainName]

Looks interesting!

I'm in two minds about the battery. Great that it is battery-powered but the 4-hour life is perhaps a bit short. That's going to mandate Ni-MH... presumably the lower 'full' voltage of these won't be a problem? Would having a built-in LiIon improve life? If so, the cost of a simple USB charge circuit may be worth it (to the user). I can appreciate that you might not want to run it when connected to a USB charger, but that situation isn't unusual enough to raise eyebrows.

[Weston]

Thanks for the feedback.

The last revision draws  ~0.35W from the battery, so 4h of battery life is probably on the conservative side. The last revision consumes more power than the previous ones because I am supplying a higher sensor voltage to increase the SNR. The boost converter runs down to ~0.7V, so a Ni-MH battery will work fine.

Lithium Ion batteries are a nightmare for small scale shipping, so that is out.

I am working on the final revision now and looking at adding a footprint for a small JST connector so people can use the probe with an optional external power adaptor.

[thm_w]

Nice to see.

Is that front loop part 3D printed or some kind of cast? How does it open?

[Weston]

The front loop is a flux concentrator which allows for sensing the current in a wire with higher accuracy than field mode. It clips on the front tip. Its 3d printed plastic, same as the tip cover, and has a gapped ferrite torroid inside.

Before you clip it on, you can put it over a wire, so there is no need to thread the wire through / cut the wire to pass it through. The opening, which determines the maximum wire you can slide it over, is 4mm. I am still working on the geometry of the plastic parts, so it might change a bit, but it's going to be something close to 4mm for the final version.

Here is a close up:


 

[salvathor]

I am working on the final revision now and looking at adding a footprint for a small JST connector so people can use the probe with an optional external power adaptor.

What about adding an USB connector? Almost any modern scope has an USB port that can be used to supply power or to charge an internal battery.

For shipping issue on Li-ion, you can simply avoid to provide battery... Simply use a standard size and left customer to add it by theirself.

[HalfSpace]

Weston, looks like a great project.

Any updates on its progress and a possible release date for crowd funding.

HalfSpace

[Weston]

Thanks for the encouragement HalfSpace!

CrowdSupply told me I need to have CE certification if I want to sell the unit outside of the USA, which was a bit of a setback. After spending a while failing to make significant progress figuring that out I have (sadly) decided not to sell outside the United States. If market demand is high enough I might do a followup campaign to make fully certified units, but right now its not worth it.

The hardware is basically entirely done, I am just working on finishing some documentation and the campaign webpage. I am hoping to have it launched by the end of the year. 

[HalfSpace]

That's a bit sad that it will only be released in the USA but I understand the cost and time issues with CE certification.

I have a question regarding the the clip/push on ferrite core. In EEVblog #296 (AIM-TTi I-Prober 520 Current Probe Review) at about the 27.50 time mark, Dave moves a current carrying wire back and forth within the attached core of the probe and noted that the current reading changed.

Does this happen with the little bee current probe?

[HalfSpace]

That's a bit sad that it will only be released in the USA but I understand the cost and time issues with CE certification.

I have a question regarding the the clip/push on ferrite core. In EEVblog #296 (AIM-TTi I-Prober 520 Current Probe Review) at about the 27.50 time mark, Dave moves a current carrying wire back and forth within the attached core of the probe and noted that the current reading changed.

Does this happen with the little bee current probe?

If this does happen, maybe a modification to the ferrite assembly could reduce any change in readings.

If a plastic bush with a slot like the attached photo is inserted in the hole of the ferrite cover so that it locks in but can be rotated, would reduce the movement of the wire being measured when the plastic bush is rotated covering the ferrites slot.

The flange on the plastic bush could be increased in diameter to match the size of the ferrite cover to make it easier to rotate.

HalfSpace

[harrimansat]

I would like to buy one as a DIY kit

Do you think it would be possible?

[Weston]

The Little Bee has officially launched on Crowd Supply! Unfortunately, I can not ship to the EU due to CE certification. However, Crowd Supply recently changed their policies so they will ship to countries outside the USA that do not explicitly require CE approval. I am currently looking into what it would take to make a future version that is CE certified, but it seems pretty complicated (and expensive...).

https://www.crowdsupply.com/weston-braun/little-bee

I also now have all the project files on github:

https://github.com/westonb/little-bee-B1

That's a bit sad that it will only be released in the USA but I understand the cost and time issues with CE certification.

I have a question regarding the the clip/push on ferrite core. In EEVblog #296 (AIM-TTi I-Prober 520 Current Probe Review) at about the 27.50 time mark, Dave moves a current carrying wire back and forth within the attached core of the probe and noted that the current reading changed.

Does this happen with the little bee current probe?

The current sensing attachment for the Little Bee is based on the same principal as the current sensing attachment as the iprober, so it has the same issue with the location of the wire shifting. I am planning on generating a sensitivity plot for the wire location. The idea of a bushing to center the wire is interesting. At this point I dont really want to change the design of the current sensing attachment, but I will have to see if I can find some existing part that works. It also should be not that hard to 3d print something out of flexible plastic.

I would like to buy one as a DIY kit

Do you think it would be possible?

Kitting everything up is a fair amount of work ( and technically does not avoid CE regulations). The whole project is open source so it should be possible for anyone to make one themselves (I think at least one ebay seller has the sensor). After the crowd supply campaign is finished I am going to see what I can do for people in the EU besides CE certification.

[harerod]

CrowdSupply told me I need to have CE certification if I want to sell the unit outside of the USA, which was a bit of a setback. After spending a while failing to make significant progress figuring that out I have (sadly) decided not to sell outside the United States. If market demand is high enough I might do a followup campaign to make fully certified units, but right now its not worth it.

A colleague and I just ordered one i-prober 520 each, which are in the mail right now. Your project would have been a nice alternative. I will follow your progress with keen interest.

I have been doing UL and CE certification for my designs for over two decades. If there is even a remote chance that the product will be sold outside the EU and might require UL, I prepare the electronics for both.
CE is different from UL in several aspects, one of those is important to you: For many applications you are permitted to do your own declaration of conformity, even without consulting a notified body. For the aforementioned applications, CE is mostly about EMC. If you know what you are doing, which I imply after looking at your design's specs, you can avoid undue emissions. Looking at your schematics, as long as the analog parts don't oscillate and forwards the signal to the oscilloscope, the PIC is the only possible, quite low power, HF-source.
As far as immissions are concerned, you simply state what your device can stand. I mean, this is an EM-field probe, so it is likely to react to EM-fields...
CE for a device like yours could be covered by a simple declaration of conformity from you. If you involve a notified body, it is still you who issues the declaration of conformity, but back it up by reports from the notified body.

Another loophole was mentioned earlier: a self-assembly kit might require no CE at all.
You might even consider just shipping certain components (mechanics, sensor, PCB). Electronics and even PCB could be sourced by the buyer through the usual channels, albeit at higher cost.

Remark regarding usability: I don't care much for batteries and wallwarts. My i-prober 520 is going to be powered by the auxiliary output of my lab power supply. USB could be a feasible connector, but we might want to provide a clean power source.

From a business standpoint I think that you made a sensible decision - feel the local market and deal with abroad later. Good luck!

[harrimansat]

I am working on the final revision now and looking at adding a footprint for a small JST connector so people can use the probe with an optional external power adaptor.

What about adding an USB connector? Almost any modern scope has an USB port that can be used to supply power or to charge an internal battery.

For shipping issue on Li-ion, you can simply avoid to provide battery... Simply use a standard size and left customer to add it by theirself.

Hi! I like your project!, thanks for share, I want tu build one, I have just buy one HMC1041Z.

It would be possible to buy you a flux concentrator and PCB´s without components?

[natman69]

Hi Weston! Congratulations it is a very interesting project!

I have some questions to ask:

1- Which are the physical dimensions of the probe tip?
I have watched your video on Crowd Supply about using the probe. I think it will be useful if you will post more examples of using the probe to measure signals on pcb in real applications. For example, how much traces on pcb must be spaced to have good measurements? Can probe tip or magnetic sensor dimensions be a limit for taking measurements on pcb in every day applications on real circuits?

2- Will you add a power connector in the final version of the probe?

3- Do you plan to design an ergonomic plastic case for the probe so users can make on their 3D printers?

Thank you!




 

[nikifena]

Great design!

Since a AA battery lasts for 4 hours what do you think about USB powering? Usually, most of the modern scopes have a USB input for an external flash drive and this could be used as a power source as well.
The well-known Micsig diff probes for example use this method for powering their units.

[RedFantom]

This indeed looks like an awesome project!

Just wanted to chip in here and say that if you were to do an EU run with either a kit or even just the sensor as it appears to be an unobtanium-type thing, I would be interested. As it stands, I will first be experimenting with some in-circuit current sensors, but I'm studying your project with interest and will hopefully learn a thing or two .

[dougg]

I have ordered one of these through CrowdSupply. On 19 March I received this notification:
https://www.crowdsupply.com/weston-braun/little-bee/updates/production-delays-due-to-difficulty-sourcing-sensors

So my April delivery has been pushed back till July. Hmm, several of my projects are being held up by this "IC shortage" (or sensor shortage in this case). And I'm getting sick of sales engineers answering a query about availability with 'How many do you expect to sell in your product' ... NONE if you don't produce them.

[harerod]

@dougg: while I am still following this thread, I am really happy with the "i-prober 520". It has really proven helpful on multiple occasions. We are so swamped with work that I am happy with anything that helps in getting the job done in less time.

[RedFantom]

That's a rough set-back indeed. The only places I found the HMC1041Z to be available was on eBay (in very small quantity, and I bought the last from the only seller I could find) and with a seller named NAC Semi, but the shipping turned out to be prohibitively expensive.

Right now I'm in the process of finding all the other components in the low quantity I need so that I can build up to three probes myself, although knowing me I'll be happy to have one properly functioning one . The AD8129 in SOIC-8 package is eluding me, for now...

[Weston]

I actually ended up ordering the sensors from NAC Semi. They have a partial reel that they acquired from someone. I checked the first and last sensors on the section of the reel that I bought and the parts from them work fine.

A lot of people are having production problems right now, but all the other important parts managed to stay in stock. The only changes I had to make were switching out the dual mosfet (for the 2nd time...) and some MLCCs.

There should be a campaign update posted on Crowd Supply and sent out to the backers as soon as the crowd supply staff review it, but the Little Bee PCBA assembly is now in production at Macrofab! All the parts have been ordered and they are currently waiting for the PCBs.

Right now the priority is fulfilling all the orders for the Crowd Supply backers, but I tacked an extra 20 units on to the PCBA order and I am going to figure out how I can get some of those extra units to interested people in Europe.

[technogeeky]

I got the notice today that the units have been shipped to Crowd Supply for distribution. I'm excited! I've wanted this kind of tool for a while!

[harrimansat]

Put me on the list for one kit to Europe!

Thanks

[piotrekd]

The front loop is a flux concentrator which allows for sensing the current in a wire with higher accuracy than field mode. It clips on the front tip. Its 3d printed plastic, same as the tip cover, and has a gapped ferrite torroid inside.

Before you clip it on, you can put it over a wire, so there is no need to thread the wire through / cut the wire to pass it through. The opening, which determines the maximum wire you can slide it over, is 4mm. I am still working on the geometry of the plastic parts, so it might change a bit, but it's going to be something close to 4mm for the final version.

Here is a close up:

Which ferrite core was used in the probe? What is the core material?
What do you think about the use of the HMC1021Z-RC in the project? Is available.

[dougg]

Received my Little Bee today and I'm trying to read the documentation. It is not obvious where the doco is in https://github.com/westonb/little-bee-B1 . My first guess was under the doc folder. When I navigated to the getting-started folder the rendered README.md file had broken links in it. For example the first link is:
https://github.com/westonb/little-bee-B1/blob/main/getting-started/doc/images/little_bee_v4_attachment.jpg
but should be:
https://github.com/westonb/little-bee-B1/blob/main/doc/images/little_bee_v4_attachment.jpg
Since all the links give blank images in my rendered README.md , I guess they all have the same path problem.

Since you have a github account, you could take some extra steps and put up that documentation in html at westonb.github.io (github has tutorials).
For example my repositories are at: https://github.com/doug-gilbert/ and the associated html documentation is at: https://doug-gilbert.github.io/ . I use LibreOffice Writer to generate (edit) html.

[Weston]

Received my Little Bee today and I'm trying to read the documentation. It is not obvious where the doco is in https://github.com/westonb/little-bee-B1 . My first guess was under the doc folder. When I navigated to the getting-started folder the rendered README.md file had broken links in it. For example the first link is:
https://github.com/westonb/little-bee-B1/blob/main/getting-started/doc/images/little_bee_v4_attachment.jpg
but should be:
https://github.com/westonb/little-bee-B1/blob/main/doc/images/little_bee_v4_attachment.jpg
Since all the links give blank images in my rendered README.md , I guess they all have the same path problem.

Since you have a github account, you could take some extra steps and put up that documentation in html at westonb.github.io (github has tutorials).
For example my repositories are at: https://github.com/doug-gilbert/ and the associated html documentation is at: https://doug-gilbert.github.io/ . I use LibreOffice Writer to generate (edit) html.

Sorry for not having this documentation up by the time the units shipped. I have a full set of operation instructions here now: https://github.com/westonb/little-bee-B1/blob/main/getting-started/README.md  Please let me know if anything in the instructions can be improved.

I have been meaning to get some sort of website up for a while now. I also have beefield.io registered. I ran into some issues last time I worked my way through the github.io hosting, I will have to try again sometime.

Which ferrite core was used in the probe? What is the core material?
What do you think about the use of the HMC1021Z-RC in the project? Is available.

The core is 5943001301 (fair-rite type 43 material) with a 8.25mm cut. I modeled a few different things and tried a few different materials. Given the gap size the material is not that critical.

The HMC1021Z is much physically larger and has 1/3 the magnetic field range. It does have the advantage of availability though.

I am not sure how many units I am going to end up making in total, but for now I have the part sourcing under control. If I were to think long term I would focus on switching to a TMR magnetic sensor. They do not have the saturation issues that AMR sensors have.



Also, just a heads up for anyone who is interested, the Little Bee units are now available for general sale through Crowd Supply and Mouser. I think there is ~35 units still left from the initial batch of 200 units I made.

[ANTALIFE]

Hey Weston

Quick question, does the sensor get damaged if it experiences saturation? By saturation I mean being in an excessive magnetic field to the point of having to be reset (RED indication LED)

Right now I am trying to measure the rise time of a solenoid current waveform, this solenoid sees a peak current of 10A and looks like it's large enough to throw the sensor off

Cheers, Anton

[e0ne199]

hello, is there any 10A-100A version of your probe? 5A is way too small for me anyway

[harrimansat]

I got the notice today that the units have been shipped to Crowd Supply for distribution. I'm excited! I've wanted this kind of tool for a while!

Hi

Can you send pcb kits to Spain?. I have boutght a magnetic sensor, i have two HMC1041Z for this project.


I have tried to buy on your page and it says that it cannot send to Spain

Thanks

Regards

Miguel

[graybeard]

Is the Little Bee project dead? 

I ordered one last year.  I received a email notice yesterday from Crowd Supply that I am being issued a refund.

Hello,

This is Tanner over at Crowd Supply! I am reaching out to you today to inform you of the latest update with the Little Bee project. Unfortunately, the expected batch has no current ETA and production has been halted for various reasons. We can always alert you, for if and when they do eventually are made available again to purchase.

So I am going to issue you a full refund and cancel your order! You should see that refund in 2-5 days. The total refunded amount is 189.91

Sorry for the inconveniences!

Regards,
Tanner
Customer Support Team
Crowd Supply

Whats up?

Chris

[natman69]

Maybe shortage of HMC1041Z magnetic sensor or other component? 

I've received the little-bee current probe with the first batch and I'am very happy with it!!!

[Weston]

Sorry for the late replies, I noticed I was not being alerted by the forum notifications.

The Little Bee has indeed been discontinued. To be honest, I was really surprised to get so many orders and am happy to have received only positive reports.

This project fell prey to CE regulations and the supply chain shortage.

CE regulations make it so the probe can not be shipped to Europe without some pretty extensive certification. As a current probe the Little Bee would be subject to even more testing than is required for generic products. Its a few hundred pages of requirements. Crowd Supply is really clamping down on this too. Despite claims to the contrary you can not say your item is a kit or development board. If you look on Crowd Supply this is pretty heavy effecting most of the recent projects.

Secondly, the supply chain shortages hit this project pretty hard. About half the active parts are out of stock. The availability of the HMC1041Z magnetic sensor is the biggest issue. I was never able to obtain the parts directly from Honeywell and the reseller I was buying small quantities from ran out of stock. This leaves 3k reels as the only option and the likelihood of making close to 3k units and recouping that is pretty small.

[harerod]

Weston, sorry to read about your problems. Chipageddon is real and I am not going into that at this point. You know that I have the TTi I-prober 520 in my lab, but I would have liked to see how your device compares.

However, regarding accreditation, I can only assume that you have fallen prey to the wrong consultants.
Both UL and CE should be pretty straightforward for a device like yours. CE will cost you a single fee, if at all, where UL, by its very nature, will produce recurring cost.
Without knowing the details, I see a typical pattern for anybody who has first, unprotected contact with a notified body. If you contact them and don't know the procedures, they have a tendency of selling you a premium package, which may prove a financial killer. This is not completely their fault. The "trick" is to know the procedures and standards, ask the correct questions and give the right answers.

It is a fact that an experienced guide will save you lots of time and frustration. What's even better, if your product meets certain requirements, you could even do a self declaration of CE CE declaration without involving a third party.

At any rate, should you want to have another go at this, I'd recommend that you look for a consultant. This forum is teeming with knowledgeable people. There is nothing magic about accreditation. However, it is important to have an idea about the pertinent standards (be it UL or CE) and build your design with those in mind.

[thm_w]

Hopefully crowd supply lets sellers simply choose to not ship to the EU if they decide.

https://www.crowdsupply.com/guide/about-ce-certification

[harerod]

thm_w - thanks for the link. I was simplified too much, in my last post. These days I mostly do medical stuff that require third party involvement. Other designs, and the Little Bee might fit in that category, do not require a notified body to become involved. However, many producers decide to get a third party certificate anyways, to reduce the potential of gross fault.
UL doesn't give us that option. With UL you pay up front and you keep paying as long as you want to keep "den Stempel" ("their seal of approval", as we lovingly say in Germany).

[Neutrion]

It makes me wonder how come that this project doesn't seems to come to fruition. Is there really no chinese company to produce it under a different name, maybe only as a self-build kit? There seems to only one overpriced seller on aliexpress.
Or everybody is taking the hard way here, downloading the plans, and buying the component one by one?