In a setup where an ESP32 reads a BME280 sensor and a laptop shows temperature, humidity and pressure live, what does each part do?

The BME280 measures, the ESP32 reads it over I2C and sends the readings on, and a client on the laptop receives and displays them in real time.

The chain has three stages, and each one does a single job:

1. Sensor (BME280). Measures temperature, relative humidity and barometric pressure, and keeps the latest readings in its registers. It does not decide when anyone reads them.
2. IoT device (ESP32). Is the bus master. It asks the sensor for fresh values over I2C, converts the raw register values into units with the sensor's calibration data, and forwards the readings off the board.
3. Laptop. Runs the receiving client (in the demo an Arduino-based one) that shows the three values as they arrive.

The split is the usual IoT shape in miniature: a cheap, dumb sensor; a small device that does the measuring and the talking; and a bigger machine that collects and presents the data. Scaling it up means a gateway or a cloud service instead of the laptop. The device in the middle stays the same.

Go deeper:

• Random Nerd Tutorials — ESP32 with BME280 — the same demo end to end, with wiring and the Arduino code that reads the sensor.
• Bosch Sensortec — BME280 — the manufacturer's page with the datasheet and measurement ranges.