Arduino Nano BLE with CN3791 charger and solar panel: step-down regulation options

Customer:

I’m planning to power an Arduino Nano BLE 33 (required for machine learning) which runs at 3.3V using a 1W solar panel and 3.7V ion battery with a CN3791 charger board. My idea is to connect the solar panel through the charger to the battery, then connect the charger output (battery) through a step-down module to power the Arduino. Is this setup correct? Am I missing any components? Can this work?

Original message (Croatian)

hvala Vam na preporuci! Imam još jedno pitanje. Radim uređaj koji koristi arduino nano ble 33 (mora biti taj zbog strojnog učenja) i on radi na 3.3 V. Da se sustav može vani sam napajati, moja ideja je spojiti solarni panel preko punjača na bateriju, a izlaz punjača (bateriju) preko step down modula na napajanje arduina. Da li je taj setup dobar, fali li mi nešto od komponenata i može li to funkcionirati? Ja sam po struci računarac, tako da se ne snalazim najbolje s elektronikom. Skica bi izgledala ovako:

Attachment omitted in migration: image.png

Originally submitted via email support on 21 July 2025. Migrated to the forum for community visibility.

Soldered Support:

It’s theoretically possible to build the device you described, but certain adjustments are needed for voltage regulation. The key challenge is finding a step-down (buck) regulator capable of reducing the voltage by such a small amount, which is difficult to achieve in practice with standard modules.

As an alternative, we recommend using an LM317 adjustable voltage regulator. With properly dimensioned resistors between the ADJ and Vout pins, you can precisely set the desired output voltage. The connection schematic and calculation formula are on the first page of the datasheet: https://www.ti.com/lit/ds/symlink/lm317.pdf

Regarding the solar panel, its efficiency depends heavily on how you use the Arduino and on available sunlight. We recommend using deep sleep mode whenever you’re not taking measurements or performing calculations, to minimize power consumption.

While the concept is viable and should theoretically provide enough energy to power an Arduino Nano BLE system, we cannot guarantee the functionality of the complete system in practice, as we have not realized such a project before. There may be deviations in actual charging efficiency and power consumption depending on conditions and components.

Original message (Croatian)

teoretski je moguće realizirati uređaj koji ste opisali, no potrebno je napraviti određenu prilagodbu u vezi s naponskom regulacijom. Ključni izazov je pronaći step-down (buck) regulator sposoban smanjiti napon za tako mali iznos, što je u praksi teško izvedivo s klasičnim modulima.

Kao alternativu preporučujemo korištenje LM317 podesivog regulatora napona, dostupan na sljedećem linku: https://soldered.com/product/lm317-adjustable-voltage-regulator/

Uz pravilno dimenzionirane otpornike između ADJ i Vout pinova, moguće je precizno podesiti željeni izlazni napon. Shema povezivanja i formula za izračun nalaze se na prvoj stranici datasheeta: https://www.ti.com/lit/ds/symlink/lm317.pdf

Što se tiče solarnog panela, njegova učinkovitost u velikoj mjeri ovisi o načinu korištenja Arduina te o dostupnosti sunčeve svjetlosti. Preporučujemo korištenje deep sleep moda kad god se ne obavljaju mjerenja ili kalkulacije, kako bi se potrošnja energije svela na minimum.
Važno je napomenuti da, iako je konceptualno izvedivo i na papiru bi trebalo biti dovoljno energije za napajanje Arduino Nano BLE sustava, ne možemo garantirati funkcionalnost cijelog sustava u praksi, jer do sada nismo realizirali ovakav projekt. Moguća su odstupanja u stvarnoj učinkovitosti punjenja i potrošnji energije ovisno o uvjetima i komponentama.