76 lines
5.8 KiB
Markdown
76 lines
5.8 KiB
Markdown
[🇩🇪 Deutsch](concept.de.md) | [🇬🇧 English](concept.en.md)
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# Concept: Modular Irrigation System
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This document describes the concept for a modular, smart irrigation system that is centrally controlled via Home Assistant.
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## 1. Architecture Overview
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The system is divided into three logical layers to ensure high flexibility and maintainability:
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1. **Control Layer (Home Assistant):** All logic, automations, and the user interface reside in Home Assistant. This is the "brain" of the system.
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2. **Gateway Layer (ESP32):** A pure protocol translator that acts as a bridge between the home network (WLAN/Thread) and the physical bus system of the plant. It contains no control logic of its own.
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3. **Actor/Sensor Layer (Slave Nodes):** Robust, specialized modules that are controlled via a bus and perform the actual tasks (switching valves, reading sensors).
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## 2. System Components
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* **Water Tank:** An IBC container serves as a water reservoir.
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* **Water Supply:** A "rain thief" on the downpipe directs rainwater into the tank.
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* **Pump:** A pump with an integrated pressure expansion tank provides the necessary water pressure.
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* **Actuators:** Motorized 12V ball valves to control the water outlets.
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* **Level Sensor (precise):** A `QDY30A` with 4-20mA output and RS485/MODBUS interface for continuous measurement of the water level.
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* **Level Sensors (Min/Max):** Optional capacitive sensors (`XKC-Y25-NPN` or similar) as redundant protection against running dry and overflowing.
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## 3. Gateway
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The central communication interface is implemented as a "dumb" gateway.
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* **Hardware:** An `ESP32C6`-based board.
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* **Function:** The gateway acts as a transparent **MODBUS TCP/IP to MODBUS RTU converter**. It receives commands from the home network and forwards them to the RS485 bus and vice versa. It does not execute its own control logic.
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* **Connection to Home Assistant:** The connection is made via the home network, either via WLAN or in the future possibly via Thread/Matter. In Home Assistant, the official MODBUS integration is used to address the gateway and the slaves behind it directly.
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## 4. Slave Nodes
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The slave nodes are the working units in the field. To keep the effort low for small series production (e.g. at JLCPCB), a universal board design for all slave types is sought.
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* **Microcontroller:** An `STM32G431PB`. Although powerful, it offers all the necessary peripherals (multiple UARTs, ADCs, CAN) and enables a uniform hardware and software design.
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* **Peripherals per Node:**
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* **Two High-Side Outputs (+12V):** Realized via a `VND7050AJ`. Perfect for controlling the 12V motor valves (`Open`/`Close`). The `Sense` line of the driver is read out via an AD converter to realize an end position detection without physical limit switches by measuring the motor current (motor current at standstill ≈ 0).
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* **Two Low-Side Outputs (0V):** Outputs switched via N-channel MOSFETs. Can be used to control 12V LEDs in buttons or to switch the solid-state relay for the pump.
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* **Two digital inputs:** Direct, protected inputs on the controller for connecting buttons or the capacitive NPN sensors.
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## 5. Bus System: MODBUS-RTU via RS485
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MODBUS-RTU is consistently used as the bus system.
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* **Reasoning:** This choice is pragmatic, as the level sensor already requires MODBUS. This means that only a single, simple and widespread protocol is required for the entire system.
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* **Physical Layer:** The cabling is done via RS485. Commercially available Cat-7 Ethernet cable with RJ45 plugs is used:
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* 1 twisted pair for the bus signals `A` and `B`.
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* 3 pairs of wires in parallel for `+12V` and `GND` to supply power to the slaves.
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## 6. Software
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* **Operating System (Slaves):** `Zephyr OS`. It is a modern, powerful real-time operating system that enables a clean and maintainable firmware structure.
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* **Logic Implementation:** The entire control logic (e.g. "If level < 20% and day of the week = Monday, then switch on valve 3 for 10 minutes") is mapped exclusively in **Home Assistant** via its automation engine.
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### 6.1. Firmware Update of the Slaves (OTA)
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The firmware of the slaves can be updated during operation via the bus without the need for direct physical access.
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* **Concept:** The `MCUBoot` bootloader is used. This is decoupled from the communication protocol.
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* **Procedure:**
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1. A script in Home Assistant reads the new firmware file (`firmware.bin`).
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2. The script breaks the file down into small data packets and sends them one after the other to the target slave via MODBUS command.
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3. The running application on the slave receives these packets and writes them directly to the secondary flash memory ("update slot").
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4. After successful transmission, the slave is restarted by command.
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5. `MCUBoot` checks the signature of the new image, copies it to the primary slot and starts it.
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* **Security:** The new firmware must mark itself as "functional" after starting. If it does not do this (e.g. due to a crash), the previous, stable firmware version is automatically restored by `MCUBoot` on the next restart by the watchdog.
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## 7. Safety and Robustness Concepts
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* **Fail-Safe Behavior:** Each slave node implements a watchdog. If no valid MODBUS query is received from the gateway over a defined period of time (e.g. 15 seconds), the slave goes into a safe state: all valves are closed and relays (e.g. for the pump) are switched off.
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* **Electrical Protection Circuits:** All external interfaces are protected. The RS485 bus lines (`A`/`B`) are protected against overvoltages with TVS diodes on each board. Inputs and outputs receive basic ESD protection.
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* **Power Supply:** The 12V bus voltage is regulated on each slave node with an efficient `TPS5430DDAR` step-down converter to the required 3.3V for the microcontroller and the bus drivers.
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