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 !!!
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? :)
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 :)