ESP32 DevKit V1 (WROOM-32)

The ESP32 DevKit V1 (WROOM-32 module) is the workhorse of do-it-yourself industrial IoT: dual-core 240 MHz, Wi-Fi + Bluetooth, a wealth of I/O and a gigantic software ecosystem, all for a few euros. It reads a sensor, does some first local processing, and reports over Modbus TCP, MQTT or OPC UA — exactly the building block of the two retrofit / OPC UA tutorials.

Limits: the WROOM-32 (LX6) lacks the vector instructions of the S3, so for heavy FFT or TinyML, the ESP32-S3 is preferable. Its internal ADCs are noisy and non-linear — for a clean analog measurement, you add an external ADC (e.g. HX711, or an ADS1115). For vision or a substantial model, you step right up to a Raspberry Pi or Jetson.