Background
The automated cleaning system for solar fields is built from two types of boards. Slave boards sit on the cleaning units themselves and operate them. The master board is the brain of the site: it talks to all slave boards over LoRa and connects the whole network to the server over Wi-Fi.
The challenge
- Two networks on one board: LoRa for long range inside the field, and Wi-Fi to the server. Both radios must work together without interfering with each other.
- Many units: each master board manages 10 to 20 slave boards, and one site can have several master boards.
- Industrial environment: 24 V cabinet power, connections to external equipment and exposure to interference.
- Field operation: a technician must see the system status immediately, without a computer.
What we built
- Processor and Wi-Fi: an ESP32 module with an external antenna connector, for a stable link to the server.
- LoRa: an SX1276 module at 917 MHz with an SMA connector for an external antenna, for maximum range in the field.
- Power supply: a 24 V input with protection and a resettable fuse, and a DC/DC converter for the board's working voltages.
- Inputs and outputs: two 24 V relay outputs, each with its own fuse, and two opto-isolated inputs for site equipment.
- Local interface: three status LEDs (link, run, status), three buttons and a buzzer.
- Service: a USB connector, a UART connector for flashing and diagnostics, and PROG and RESET buttons.
- Firmware: managing the network of slave boards, and passing data and commands between the server and the field.
- Remote updates: the master receives a new version from the server over Wi-Fi and passes it to all slave boards over LoRa. The LoRa channel is very slow and allows transmitting only 1% of the time, so the master broadcasts the update to all units in parallel, at a fixed rate under the limit, and completes for each unit only what it is missing. About the update mechanism.
The result
One board that connects a whole field of cleaning units to the server, allows the entire site to be managed remotely, and updates the version of every unit without going to the field.
