Normally when you think solar projects, you think of big photovoltaic cells. But a photodiode is just an inefficient, and usually much smaller, PV cell. Since [Pocket Concepts]’s Solar_nRF has such a low power budget, it can get away with using BPW34 photodiodes in place of batteries. (Video, embedded below.)
The BPW34 silicon PIN photodiode feeds a small voltage into a BQ25504 ultra-low-power boost converter energy harvester which stores power in a capacitor. When the capacitor is fully charged the battery-good pin is toggled which drives a MOSFET that powers everything downstream.
When it’s powered on, the Nordic nRF initializes, reads the current temperature from an attached I2C thermometer, and then sends out a Bluetooth Low Energy (BLE) advertising packet containing the temperature data. When the capacitor runs out of energy, the battery-good pin is turned off and downstream electronics become unpowered and the cycle begins again.
[Pocket Concepts] uses a Nordic Semiconductors Power Profiler Kit II to help determine charge requirements. He calculates that 37 uF would be enough power for a single cycle, then uses 100 uF to get between one and three transmissions done using a single charge.
[Pocket Concepts] finishes his video with a request for project ideas. Is this a soil moisture meter? Earrings that monitor your biometrics? Something else? If you have some ideas of your own please sound off in the comments!
[Pocket Concepts] said he was inspired by Ultra low power energy harvester from BPW34 over on Hackaday.io, be sure to check that out for some interesting low-power project ideas. If you’re interested in other applications for Nordic nRF chips check out ESP32 Turned Handy SWD Flasher For NRF52 Chips and Ground Off Part Number Leads To Chip Detective Work for some examples.
It´s a good old trick, but the star of the show here is not the BPW34, it´s the incredible BQ25504 !!!
I also like much the BQ25570, it starts harvesting energy with a low low 100mV and is more versatile, but 3x the price
Such a beautiful application of BLE utilizing the handshake procedure as a data broadcast, but would you really call this battery free if a large capacitor is used as a battery? I might just be being pedantic, cool project nontheless.
Yeah a little bit pedantic, but maybe. Solar is not known for providing a stable, set voltage so it makes sense having a cap in place to smooth things out.
Is every desktop PC then battery-operated, with built-in charger? :)
Yes it runs on battery 50 to 60 times a second
with a bridge rectifier even 100 to 120 times ;-)
I suppose everything on planet Earth (and several things outside of it) is battery-operated via chemical or nucleic reservoirs charged up by the sun or previous supernovae and quasars.
It’s a bit Neil deGrasse Tyson redditoid to say it, but at least it’s basically true
Not exactly a large capacitor… Sure it is acting a bit like a battery as it really is in use as an actual power storage device rather than the usual power smoothing role for a small cap. But calling that sort of scale of Cap ‘large’ seems a stretch to me – Not the smallest capacitor you can possibly get by any stretch, but when its still a SMD capable cap value IMO that discounts it from being ‘large’ or really comparable to battery – smallest batteries you can actually get are likely bigger than a suitable cap, and the expected image folks will have in their mind for even a small battery is something like a watch battery, maybe that through hole cap sort of size cylinder battery some wireless earbud and the like have.
It’s not a super capacitor, only 100 uF. So I’ll allow it
I need meshtastic/reticulum/meshcore node similar model. Harvesting energy, quick exange data and sleep. No problem, my message will be ‘walking’ 20 min not now, but without a battery (meybe super capacitor)
Need something that keeps the message while unpowered. FRAM?
Nice, useful. I’m putting this into my digital Must Remember file. Thx.
You could also be pedantic to argue that it is battery free, as the original use of “battery” meant a collection of multiple cells (or capacitors) and this only has one :)
Ah ha! That is how I think of battery. But I also just read a book about the tactics of the American Civil War. So after that it really feels odd to use battery in a non plural sense.
Whatever the case I probably wouldn’t call the single capacitor cell a battery but I’d be amiable to an individual who called a series of capacitor cells a battery. Also I’d just give the maker the benefit of the doubt.
I have a different definition of battery in mind, but I also just caught charges for assaulting a hobo. So after that it really feels odd to use battery in a non-beating-a-guy-up sense.. He had it coming… You might have won round two, ol’ Dancing Jiminy Jones, but we’ll see who gets the last laugh in round three…
What is that tool in the photo? Just some kind of pointer?
Nevermind, just a pen.. tip looked like plastic
I had a doodad that periodically ran a PIC16C84** from 6x BPW34’s in series across a 470uF cap when it charged up. By feeding MCLR through a diode, it would come out of reset between 2.5 and 3V. From memory they ran down to less than a volt, but the ouput fets couldn’t drive anything at that point, so you had to get the output driving done before VDD got too low.
The prototype used a germanium transistor step up with a single 10mm photodiode, but 6x BPW34’s were a lot easier and cheaper…
**(Yes it was a long time ago)
The article was good, but the youtube video is straight-up clickbait. Also, he’s not using a “photodiodes in place of batteries”, he’s using a capacitor in place of batteries, and photodiodes in place of a charger.
A very semantics and definitions argument – IMO the nature of battery powered devices is that they can function without the charger connected, which this really doesn’t if you are going to call the photodiode the charger.
And for me if its integral to the device and it functions stand alone that would make whatever its power source is that device’s ‘battery’ in common language terms even if not in technically EE approve language for the components in question – it is functioning as the source of electrical energy for the portable device in question, and that is what most people think a battery is a standalone electrical source. (at least when considering battery in the electrical sense rather than in the gun battery or any other sense of the word, as its got around a fair bit)