• RE: 💬 The Harvester: ultimate power supply for the Raybeacon DK

    @Mishka Looks as though an array of BPW34 can actually be packaged together fairly tightly.
    alt text
    It still wastes some real estate, but not as badly as what I had imagined.

    I suspect they wouldn't do well under indoor LED lighting though, as they seem to have peak sensitivity at around 900nm, which is infrared.

    posted in OpenHardware.io
  • RE: 💬 The Harvester: ultimate power supply for the Raybeacon DK

    Maybe the reason solar cells like the SC-1338-4 are so elusive to find in the usual parts market is that the manufacturer is basically just buying a relatively cheap 5x5 or 6x6 inch slice of monocrystal that probably looks like:
    alt text
    and then carefully breaking it into bits of such a size that when wired together they exactly fit whatever net size the buyer wants. Though I've never tried it, I presume that you or I could be doing very small scale "manufacturing" ourselves if we were so inclined. Obviously some people make their own DIY 100w panels this way, but from what I've seen those people do so by soldering foil tapes across the front face of the monocrystalline slices, which presumably these cells would be too small to do. Hmmmm...., this now has me curious as to exactly how the bits get wired together. Anyway, provided they're not too hard to make, the upside to DIY'ding small solar cell planels would be getting any size/voltage combination we want plus freedom from having to scavenge pre-made cells from pricier consumer products.

    posted in OpenHardware.io
  • RE: What did you build today (Pictures) ?

    @xmonika Nice work! I really like how you very artfully leveraged pre-made boards into such a compact assemblage. Is the backplane something that you self etched or CNC'd?

    posted in General Discussion
  • RE: Everything nRF52840

    It turns out that the very first solar powered watch, made by Seiko in 1969, had a side read display:
    alt text
    Though it gives up valuable display real estate, maybe that style would be easier to DIY in a form that wouldn't be too large to wear without embarrassment. I kinda like it myself: in theory I could check the time without having to turn my wrist.

    posted in Hardware
  • RE: 💬 The Harvester: ultimate power supply for the Raybeacon DK

    @Mishka Looks very promising!

    Thanks for posting the charts and the photo. I tried googling the "SC-1338-4" but found no datasheet, no sellers, nothing. I'm guessing the SC probably stands for "solar cell". Is it by any chance 13mm x 38mm in size? I'm only guessing, but perhaps the 4 is a reference to 4v, which is perhaps the voltage at maximum solar illumination. In that case, what appears to be a part number ("SC-1338-4") is actually just a generic description of the part, not a true manufacturer part number.

    The only other clue as to which solar cell is might be is perhaps a barely visible logo in your photo of the cell. The logo looks like the mirror image of "CAT" with a kind of triangle pushing up the bottom of the "A" letter.

    By the way, it looks like an interesting source for truly tiny scavenged solar cells might be solar watches:
    alt text
    That solar cell looks tinier than any that I've ever seen for sale.

    posted in OpenHardware.io
  • RE: 💬 The Harvester: ultimate power supply for the Raybeacon DK

    @Mishka Well, since you ask, I think the EM8500 would be interesting to try: https://www.emmicroelectronic.com/sites/default/files/products/datasheets/8500-ds.pdf

    I only recently discovered it, but the datasheet says it can self-start with an input voltage of 300mv and a mere 3 microwatts. Once started, the datasheet says it can continue functioning on as little as 100mv and 1 microwatt. It also claims to include MPPT.

    The other one that would be interesting to try would be the EM8900, which can self start with an input voltage as low as 5mv, which is, AFAIK, the lowest of any available commercial chip.
    https://www.emmicroelectronic.com/sites/default/files/products/datasheets/8900-ds.pdf
    However, for a solar cell as small as your solar bit, it would require extra circuitry to operate it in burst mode, because at 5mv the micro-ampere requirements would likely exceed what your solar bit could deliver on a continuous basis. It's the same issue as with the LTC3108: https://www.openhardware.io/view/732/Extreme-Energy-Harvester

    I haven't yet tried a solar cell scavenged from a solar calculator, but that might be interesting to try as well, since presumably those are well designed to work with indoor lighting and have been perfected over decades for that use since the 1970's. Unfortunately, I don't know of any that can be purchased outright instead of as part of a solar calculator, like say the FX-260 or similar. Maybe someone reading this knows of a source?

    Though it's cheating, the last option would be to use a long-lived button battery purely to avoid cold-boot scenarios and to manage the collection of real solar power during those times. I imagine that such a battery could be quite small if limited to that type of use. Some such batteries might last as long as 40 years, such as Tadiran. That said, if it were deprived of light for long enough, it would probably run the battery down sooner than desired, so I don't like this option.

    posted in OpenHardware.io
  • RE: What did you build today (Pictures) ?

    @monte I think it may run into the same barrier I encountered with both uPython and FORTH and uLISP. I got them all to do FOTA with nRF52, which is easier because they are interpreted, but in none of the cases could I easily leverage the wonderfully extensive arduino sensor libraries because those are written in C. Apparently there do exist ways to do it with linkers and such, but I wouldn't classify it as easily done. More like "easier said than done." uLISP would have been the easiest to adapt C-libraries, but it's a slow inefficient implementation of LISP, so that was a downside. Although practically anything can be made to work given enough time and effort, there's something to be said for staying within the Arduino framework so as to minimize time and effort.

    That said, maybe your idea is different. Sometimes it's hard to really know until you explore it a bit.

    posted in General Discussion
  • RE: What did you build today (Pictures) ?

    @Nca78 Just FYI, I looked into attempting a FOTA on the nRF52 but at the time I didn't feel as though I had enough easy-to-follow information to do it within the limited spare time available. I think adafruit may have some kind of FOTA for the nRF52 with their circuitPython project, but that language's runtime is awfully slow compared to C or FORTH.

    posted in General Discussion
  • RE: What did you build today (Pictures) ?

    @zboblamont Ah, you got bit by my main reason for not liking Domoticz: Domoticz would be so much more useful without that 5 minute minimum between recorded datapoints. It's a wonder they've never fixed that.

    posted in General Discussion
  • RE: What did you build today (Pictures) ?

    @NeverDie said in What did you build today (Pictures) ?:

    @Nca78 Looked at another way, once installed and sealed up it will also be a sort of time capsule. 👍

    I said hidden and not sealed. Unless you have worked really hard on the FOTA for nrf52 ? 😛

    posted in General Discussion