Powering mote 24/7 using only a supercap and solar


  • Hero Member

    Anyone already doing it?

    Seems like all that's needed is a supercap with low enough leakage current such that harvested solar energy exceeds leakage current per 24 hour cycle.

    Yesterday I ordered a few boost converters to play around with: an AAT1217, an LTC3105, an MP3418, and an L6920DTR. Out of those four different boost converters, hopefully at least one will prove adequate. Maybe all of them will. Either way, I'm sure to learn something about what's ultimately needed.

    I checked the unloaded voltage on an el cheapo solar cell (scavanged from a $1 garden light), and it came out around 1v under indoor ambient light conditions, near a window on a darkly overcast, rainy day with no indoor lights on. That's higher than what I was expecting. Of course, how much of that is ephemeral and how much of it is solid under load remains to be seen, and I guess that's part of what I'll be learning.

    alt text
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    For illustration purposes, I put a little TH mote inside it.


  • Hero Member

    For a blocking diode, I'll probably use this: http://www.digikey.com/product-detail/en/toshiba-semiconductor-and-storage/CUS520,H3F/CUS520H3FCT-ND/5114381
    because it's only 21 cents, quantity 1. 280mv forward voltage drop. At most 1uA reverse flow current.

    That said, a more interesting (though a lot more expensive) choice would be: http://www.ti.com/lit/ds/symlink/sm74611.pdf
    which has a forward voltage drop of just 28mv, and a similar maximum reverse current.


  • Hardware Contributor

    one of the best part i know for this is also the BQ25504. One of the most efficient i think.
    I'm designing a board for solar ;) so i've studied a bit alternatives for my usecase.
    Best is to fit an app, because there are always lot of dilemma and compromise regarding solar panel used, input voltage, effiency not always the same with MPPT, and cost...not so simple,
    There are also multiple solar charger boards which exist like the adafruit or the lipo rider, more simple but can do the job too etc...
    Lot of articles about this on internet too.
    These low input voltage are nice, but it's not a big harvest. for indoor, with all packet exchange we have for a transmission can be critical. Then you can do battery extender etc.. but add cost.
    For outdoor a bit easier, and perhaps does not need expensive ic to run etc..


  • Hero Member

    @scalz said:

    one of the best part i know for this is also the BQ25504. One of the most efficient i think.
    I'm designing a board for solar ;) so i've studied a bit alternatives for my usecase.
    Best is to fit an app, because there are always lot of dilemma and compromise regarding solar panel used, input voltage, effiency not always the same with MPPT, and cost...not so simple,
    There are also multiple solar charger boards which exist like the adafruit or the lipo rider, more simple but can do the job too etc...
    Lot of articles about this on internet too.
    These low input voltage are nice, but it's not a big harvest. for indoor, with all packet exchange we have for a transmission can be critical. Then you can do battery extender etc.. but add cost.
    For outdoor a bit easier, and perhaps does not need expensive ic to run etc..

    Yeah, the BQ25504 does appear to offer nice functionality. But at 3x3mm in size, I'm afraid it would be challenging to solder it. Is it available in a larger package or pre-soldered onto a breakout board?


  • Hero Member

    Well, answering my own question, it looks as though there is at least one breakout board for it: https://www.tindie.com/products/onehorse/bq25504-solar-cell-lipo-charger/
    Sticker shock though.

    Also, there's this breakout based on the LTC3108, but be prepared for sticker shock again: https://www.crispytronics.com/collections/energy-harvesting/products/energy-harvester-breakout-100-mv-startup?variant=882155101


  • Hardware Contributor

    yep i know these, look nice ;) all depends of the usecase like i said


  • Hero Member

    I'm quite impressed with Digikey. I ordered the above parts on Tuesday (2 days ago), for just regular First Class mail delivery, and the parts arrived today already. Cool!

    Anyhow, all these parts are so small that I'll need to create some custom breakout boards for each of them in order to do any testing. I do hope that regular tack and drag hand soldering works on parts this small. Otherwise, I'll have to build a reflow oven out of a toaster oven, and that might mean further delay.


  • Hero Member

    @NeverDie said:

    @scalz said:

    one of the best part i know for this is also the BQ25504. One of the most efficient i think.
    I'm designing a board for solar ;) so i've studied a bit alternatives for my usecase.
    Best is to fit an app, because there are always lot of dilemma and compromise regarding solar panel used, input voltage, effiency not always the same with MPPT, and cost...not so simple,
    There are also multiple solar charger boards which exist like the adafruit or the lipo rider, more simple but can do the job too etc...
    Lot of articles about this on internet too.
    These low input voltage are nice, but it's not a big harvest. for indoor, with all packet exchange we have for a transmission can be critical. Then you can do battery extender etc.. but add cost.
    For outdoor a bit easier, and perhaps does not need expensive ic to run etc..

    Yeah, the BQ25504 does appear to offer nice functionality. But at 3x3mm in size, I'm afraid it would be challenging to solder it. Is it available in a larger package or pre-soldered onto a breakout board?

    I've changed my mind. I want to try the BQ25504. Why? Well, it turns out a guy in Switzerland has already done more or less the experiment that I was going to do, and this is his conclusion:
    alt text
    (http://www.limpkin.fr/index.php?post/2011/12/07/Indoor-solar-energy-harvesting%3A-a-platform-to-(finally)-get-some-numbers)

    LOL. So, regardless of soldering difficulty, the BQ25504 looks like it's sufficiently better that it's worth pursuing.

    However, TI's eval board for the BQ25504, is a totally insane $99. So, it's either DIY, or else find some other BQ25504 board that's priced more sensibly. There is one on Tindie that I've already mentioned (above). Any others worth considering?


  • Hero Member

    Fortunately, I notice that the author of the Tindie product has posted his PCB on OSH PARK: https://www.oshpark.com/shared_projects/tksisJZ6 An order for 3 PCB's costs a total of just $1.25. Nice!


  • Hero Member

    As for soldering the BQ25504 chip, must I use a reflow oven, or will careful hand soldering (e.g. tack and reflow) be effective?


  • Hero Member

    OSH PARK is the gift that keeps on giving. I found an even simpler BQ25504 breakout board here: https://oshpark.com/shared_projects/CYdxpE9S
    Costs just $0.65 for 3 boards.
    The design files are here: https://github.com/bootchk/BQStripped


  • Admin

    @NeverDie And bootchk designed it using KiCAD - well done! As a side note, in the very early days of the MySensors core team (@hek, @tbowmo, @Anticimex and I) decided that, in the spirit of open source, to abandon commercial / proprietary CAD programs for the MySensors official board designs, hence why SenseBender Micro is in KiCAD and the forthcoming gateway will be too. We wanted to ensure that all board designs would be available to users freely for modification and improvements. While KiCAD is the standard for the official MySensors board designs, it would be nice to see broader adoption by the MySensors community as well (as I step down from my soapbox) ;)


  • Mod

    @NeverDie said:

    As for soldering the BQ25504 chip, must I use a reflow oven, or will careful hand soldering (e.g. tack and reflow) be effective?

    At first sight the footprint looks identical to that of nrf24 (on phone, so didn't check).
    These can be handsoldered, with a fine soldering tip.


  • Hero Member

    @NeverDie said:

    https://www.tindie.com/products/onehorse/bq25504-solar-cell-lipo-charger/

    I ordered the OSH PARK boards, but I also ordered one of the pre-made BC25504 boards from Tindie (https://www.tindie.com/products/onehorse/bq25504-solar-cell-lipo-charger/). Considering that it's already fully assembled, and considered how much time it took me to layout the LTC3105 board, I think the price isn't unreasonable. If it "just works" right out of the box, then it's worth it to me. Also, the OSH PARK boards will take about two weeks to arrive. Hopefully the Tindie arrives a lot sooner than that. If I like it, then I'll order the BC25504 components from Digikey, which should arrive quickly.

    Anyone else here used or tried the BC25504?


  • Hero Member

    @blacey said:

    @NeverDie And bootchk designed it using KiCAD - well done! As a side note, in the very early days of the MySensors core team (@hek, @tbowmo, @Anticimex and I) decided that, in the spirit of open source, to abandon commercial / proprietary CAD programs for the MySensors official board designs, hence why SenseBender Micro is in KiCAD and the forthcoming gateway will be too. We wanted to ensure that all board designs would be available to users freely for modification and improvements. While KiCAD is the standard for the official MySensors board designs, it would be nice to see broader adoption by the MySensors community as well (as I step down from my soapbox) ;)

    I'm using Diptrace, but it isn't very good for sharing source files with other users, not even other Diptrace users. Doing so involves some rather cumbersome export and inport of components and patterns, and then re-linking the two afterward. On the plus side, though, it was very easy to learn. Anyhow, it seems that all the major PCB design tools have free versions for hobbyists. Hopefully if you know one, it's much easier to learn another if the need arises.


  • Hero Member

    @Yveaux said:

    @NeverDie said:

    As for soldering the BQ25504 chip, must I use a reflow oven, or will careful hand soldering (e.g. tack and reflow) be effective?

    At first sight the footprint looks identical to that of nrf24 (on phone, so didn't check).
    These can be handsoldered, with a fine soldering tip.

    Thanks! Your optimistic post motivated me to pull the trigger on ordering the OSH PARK boards.


  • Hardware Contributor

    @NeverDie
    good choice ;)
    i also read this article. i have some BQ25504 sample, but for the moment i'm not using (even if i did the eval board!) as it was not fitting my usecase, and cost goals. And for a simple button mote, i would prefer a power supply without regulator...enough years lifetime for me and no additional cost with ic + supercap (which need to be mF or F!) + solar cell (and it's size even for small). Add to this that sun/light exposure/placement is critical indoor or harvesting nothing.

    Another sidenote, we also need to take in account the power it needs for packet transmission including retries + signing (which can be n*100ms..). no problem if there is an additional batt or if it's a simple sensor without ack. otherwise, it may need an additional batt in the cost.

    But it's still a cool ic, nice project :)


  • Hero Member

    @NeverDie said:

    @NeverDie said:

    https://www.tindie.com/products/onehorse/bq25504-solar-cell-lipo-charger/

    I ordered the OSH PARK boards, but I also ordered one of the pre-made BC25504 boards from Tindie (https://www.tindie.com/products/onehorse/bq25504-solar-cell-lipo-charger/). Considering that it's already fully assembled, and considered how much time it took me to layout the LTC3105 board, I think the price isn't unreasonable. If it "just works" right out of the box, then it's worth it to me. Also, the OSH PARK boards will take about two weeks to arrive. Hopefully the Tindie arrives a lot sooner than that. If I like it, then I'll order the BC25504 components from Digikey, which should arrive quickly.

    Anyone else here used or tried the BC25504?

    To his credit, the Tindie seller shipped it the same day I ordered, and tracking shows I should be receiving the pre-made BC25504 board tomorrow. :)


  • Hero Member

    I received the BQ25504 pre-made board from Tindie, and gosh it's small:
    0_1479601957884_BQ25504_pesky.jpg
    I guess my purchase of the PCB's from Osh Park was a waste, because I don't see how I could solder discrete parts which are that tiny. Any ideas?


  • Admin

    @NeverDie said:

    I guess my purchase of the PCB's from Osh Park was a waste, because I don't see how I could solder discrete parts which are that tiny. Any ideas?

    Reflow oven - http://makezine.com/2015/04/15/diy-open-source-reflow-oven/ As an aside, I just had lunch with Peter Easton last week, the inventor of ControlLeo, and he owns the DIY reflow oven market so you can't go wrong. Of course, I built one a couple years ago :+1:


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