An interesting new accessory appeared on my desk recently in the form of a solar power supply for the micro:bit.
The power supply, designed by Seenov, consists of a rechargeable battery with a associated circuit board and solar cell and provides a regulated output of 3.3 volts. Their aim was to provide a environmentally friendly way of powering a micro:bit to reduce the dependency on single use batteries.
So whats in the box?
- 1600mAh Lithium Polymer battery
- Control circuit with:
- Battery Voltage Monitor
- Solar Voltage Monitor
- Solar Current Monitor
- USB charging circuit
- Charger on/off
- Solar Panel
The battery is contained in a small case with the controller circuit attached on top. The solar panel attaches via a JST connector to the board.
For ease of use an old DVD case was press-ganged into service. The solar cell was placed between the case and the cover with the battery and circuit being placed inside the case. To keep the solar cell angled a small straw was used to prop the case open.
Placing on the window ledge with the solar panel facing the sun, a LED lit up showing that power was being generated and the battery was being charged. After a few hours charge a micro:bit was connected which ran the 'out of the box demonstration code' function as expected.
For times when the sun is not sufficient for charging, the charger circuit has a micro USB connection to charge from a USB connection.
The controller circuit breakouts the battery voltage and the voltage and current being supplied from the Solar panel. This allows the monitoring of the state of the power supply via the micro:bit.
The original plan was to connect the micro:bit to a BME280 i2c weather sensor but the one that was in the spares box appeared to have died and would not respond to any commands. Another one has been ordered and, once arrived, will form the basis of a weather monitoring station.
However using a micro:bit playground with the traffic lights posed no problems to the battery.
In essence this is no different to running the micro:bit from two 'aaa' batteries but with this you can, as long as there is sunlight, power your micro:bit for nothing. It's going to be interesting to see what ideas will be thought of and where this solar battery will turn up.