Solution Architecture
The solution will have two variants:
Variant 1: Node-RED Low-code Platform
The first, simpler variant will have three circuits, two with the Arduino Nano and one with the Raspberry Pico. Each microcontroller board will be connected to a Raspberry Pi or a personal computer running the Node-RED low-code platform. The boards will send data to Node-RED over simple serial communication. Node-RED will connect to a WiFi network and exchange data with the MQTT broker on the cloud which will exchange data with the mobile IoT app. In this variant there will be no data exchange with the IoT app over BLE, hence the fourth cricuit using the ESP32 will not be required.
Variant 2: Inter-board Communication
The second, more complex variant will have four circuits, two with the Arduino Nano, one with the Raspberry Pico, and one with the ESP32. The ESP32 will be programmed to connect to a WiFi network and exchange data with the MQTT broker on the cloud which will exchange data with the mobile IoT app. The ESP32 will also be programmed to exchange data with the mobile app over BLE. One Nano and the Pico will use the UART protocol for inter-board data exchange with the ESP32 and one Nano will use the LoRa protocol for data exchange with the ESP32.
The diagram below illustrates both variants.
