I stumbled on the XIAOMI Mijia Bluetooth Thermometer LYWSD03MMC as i wanted to monitor room temperature and humidity via bluetooth low energy.
I found two really awesome projects which enable custom software on the LYWSD03MMC.
As i really dislike the usage of batteries in low power devices (Even if they last months or years) i wanted to power this tiny devices with a mini solar panel and a supercapacitor.
The case needs minor modifications to be able to connect the solar panel with wires.
Note: When viewing the LCD the wires should be exit the case on the left side. The BLE antenna is on the right and i expierenced a worse RSSI while the first attempt to exit the wires on the right side.
Just solder GND and Voltage wires a shown. Dont forget to place in a diode, this is necessary that the solar panel does not discharge the Supercap overnight.
Remove the "-" pin from the supercapacitor. And carefully bend the "+" pin down. The capacitor fits into the slot of the CR2032.