A balcony weather station with two sensors and no cloud
I wanted to know whether to take a jacket, and I wanted the answer to come from my own balcony rather than from an airport twenty kilometres away. The result is a small white box that has now survived one winter.
Parts
| Part | Why |
|---|---|
| ESP32 dev board | Deep sleep draws next to nothing |
| BME280 | Temperature, humidity and pressure in one package |
| Tipping-bucket rain gauge | A reed switch — nothing to calibrate |
| 18650 cell + small solar panel | Runs through the dark months, barely |
The board wakes every five minutes, takes three readings, sends the median over MQTT and goes back to sleep. Taking the median rather than the mean matters: about one reading in two hundred is nonsense, and a mean would smear that nonsense into the chart.
weather/balcony/temperature 3.4
weather/balcony/humidity 87
weather/balcony/pressure 1012.6
weather/balcony/battery 3.91Things that went wrong
Self-heating. With the sensor on the same board as the regulator, readings were two degrees high. A 15 cm ribbon cable to move the sensor away solved it.
Sun. A white box in direct sunlight is an oven. The sensor now lives inside a stack of upturned plant saucers, which is an ugly but respectable radiation shield.
Winter. At −14 °C the cell delivered roughly a third of its capacity. Stretching the interval to fifteen minutes whenever the battery drops below 3.6 V was enough to get through January.
What I use it for
One small dashboard, and one automation that tells me to close the window when it starts to rain. That is all, and that is plenty.