Every now and then I need to know basic climate data, mostly temperature and humidity. Often, I like to see how the behaviour is over time, so logging (to MQTT) is also welcome.

I built a small device using well-known building blocks: ESP8266 (Wemos D1 mini), BME280 sensor and a small OLED display. With an old phone battery, it can be operated anywhere.

The software is quite basic (code is on codeberg.org). If the metering mode is selected using the switch on the back, every 5s the data is measured and updated on the display. In logging mode, the data is collected every 15min and sent to the MQTT broker. In between the sensor and the display are switched off and the ESP goes into deep sleep.

The battery doubles as stand. Using the jumper on the back, the device boots (after reset) into OTA mode. So the software can be updated easily.

The perfboard has the size of a credit card. Openings into the board reduce the overall thickness and protect both display and sensor.