DIY Solar-Powered Xiaomi Bluetooth Sensor

If you're interested in DIYing a Xiaomi Bluetooth temperature and humidity sensor, this article is for you.

The Xiaomi Bluetooth sensor that uses a CR2032 battery often runs out of power quickly, meaning you have to replace the battery frequently. So how can you fix this?

If you have a small solar panel and a 5.5V 2.2F supercapacitor, you can combine them with a Schottky diode to DIY a Xiaomi Bluetooth temperature and humidity sensor with virtually unlimited battery life.

The solar panel's short-circuit current indoors is about 1mA, and the maximum voltage can reach around 4 volts.

After testing, running it overnight results in about 2.5V in the morning, enough for the display to work normally. However, by noon, the display starts to show some ghosting, and the voltage measures around 3.8V at that time.

To stabilize the voltage, you can add a voltage clamp. You'll need a small LED—at around 2.4V, the current drops to zero—and then add a 1N4007 diode in series, which starts conducting at about 3V, connected across the capacitor terminals.

With this setup, the temperature and humidity sensor will run properly and continuously.

Done!