Author Topic: Little Bee Current Probe  (Read 2279 times)

0 Members and 1 Guest are viewing this topic.

Offline Weston

  • Regular Contributor
  • *
  • Posts: 107
  • Country: us
Little Bee Current Probe
« on: September 25, 2020, 10:44:17 pm »
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.
 
 
The following users thanked this post: thm_w

Offline dunkemhigh

  • Super Contributor
  • ***
  • Posts: 2393
Re: Little Bee Current Probe
« Reply #1 on: September 27, 2020, 12:33:02 am »
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.
 

Offline Weston

  • Regular Contributor
  • *
  • Posts: 107
  • Country: us
Re: Little Bee Current Probe
« Reply #2 on: September 28, 2020, 06:07:39 pm »
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.
 
The following users thanked this post: dunkemhigh

Offline thm_w

  • Super Contributor
  • ***
  • Posts: 2405
  • Country: ca
Re: Little Bee Current Probe
« Reply #3 on: September 28, 2020, 08:48:01 pm »
Nice to see.

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

Offline Weston

  • Regular Contributor
  • *
  • Posts: 107
  • Country: us
Re: Little Bee Current Probe
« Reply #4 on: September 30, 2020, 02:35:14 am »
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:


 
 
The following users thanked this post: thm_w

Offline salvathor

  • Contributor
  • Posts: 9
  • Country: it
Re: Little Bee Current Probe
« Reply #5 on: October 09, 2020, 07:12:24 am »

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.



 

Offline HalfSpace

  • Regular Contributor
  • *
  • Posts: 115
  • Country: au
Re: Little Bee Current Probe
« Reply #6 on: November 20, 2020, 11:00:22 pm »
Weston, looks like a great project.

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

HalfSpace
"He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever."
 

Offline Weston

  • Regular Contributor
  • *
  • Posts: 107
  • Country: us
Re: Little Bee Current Probe
« Reply #7 on: November 21, 2020, 10:56:14 pm »
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. 
 

Offline HalfSpace

  • Regular Contributor
  • *
  • Posts: 115
  • Country: au
Re: Little Bee Current Probe
« Reply #8 on: November 22, 2020, 02:36:35 am »
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?
"He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever."
 

Offline HalfSpace

  • Regular Contributor
  • *
  • Posts: 115
  • Country: au
Re: Little Bee Current Probe
« Reply #9 on: November 24, 2020, 06:39:59 pm »
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
"He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever."
 

Offline harrimansat

  • Regular Contributor
  • *
  • Posts: 138
Re: Little Bee Current Probe
« Reply #10 on: December 21, 2020, 04:43:31 pm »
I would like to buy one as a DIY kit

Do you think it would be possible?
 

Offline Weston

  • Regular Contributor
  • *
  • Posts: 107
  • Country: us
Re: Little Bee Current Probe
« Reply #11 on: December 23, 2020, 04:59:50 am »
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.
 
The following users thanked this post: thm_w

Offline harerod

  • Newbie
  • Posts: 3
  • Country: de
Re: Little Bee Current Probe
« Reply #12 on: December 23, 2020, 08:43:29 pm »
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!
« Last Edit: December 23, 2020, 08:55:46 pm by harerod »
 
The following users thanked this post: harrimansat

Offline harrimansat

  • Regular Contributor
  • *
  • Posts: 138
Re: Little Bee Current Probe
« Reply #13 on: January 02, 2021, 06:10:07 pm »

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?
 

Offline natman69

  • Contributor
  • Posts: 29
  • Country: it
Re: Little Bee Current Probe
« Reply #14 on: Yesterday at 06:51:20 am »
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!




 
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf