81 lines
2.9 KiB
Markdown
81 lines
2.9 KiB
Markdown
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# as5600_node — AS5600 12-bit Magnetic Rotary Encoder (C++, I2C)
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ROS2 node for reading AS5600 magnetic rotary position sensors via Linux I2C (`ioctl`). Publishes angle data periodically. Supports multiple encoders on separate I2C buses.
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**Platform:** linux-aarch64 only (Raspberry Pi)
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## ROS2 Interface
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| Direction | Topic | Message | Description |
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|---|---|---|---|
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| Publish | `/encoder/state` | `EncoderRead` | Periodic angle readings per encoder |
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```
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# EncoderRead.msg (as5600_node → executor)
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uint8 encoder_id # Encoder index (0, 1, 2, ...)
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float32 angle # Angle in degrees (0.0-360.0)
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uint16 raw_angle # Raw 12-bit value (0-4095)
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```
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## Parameters
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| Parameter | Type | Default | Description |
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|---|---|---|---|
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| `i2c_devices` | string[] | `["/dev/i2c-1"]` | List of I2C device paths, one per encoder |
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| `publish_rate` | double | `10.0` | Publish frequency Hz |
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## File Structure
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```
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src/as5600_node/
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├── CMakeLists.txt # ament_cmake — NO external lib dependency
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├── package.xml # depend: rclcpp, blockly_interfaces
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├── include/as5600_node/
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│ └── as5600_node.hpp # As5600Node class + I2C helpers + register constants
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└── src/
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├── as5600_node.cpp # I2C init, timer_callback, read_raw_angle
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└── main.cpp # rclcpp::spin(node)
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```
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## Build & Run
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```bash
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pixi run build-as5600 # installs system deps (apt) + builds
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pixi run as5600-node # start node with default parameters (1 encoder)
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# 3 encoders on separate buses, 20 Hz
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source install/setup.bash
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ros2 run as5600_node as5600_node --ros-args \
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-p i2c_devices:="['/dev/i2c-1', '/dev/i2c-3', '/dev/i2c-4']" \
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-p publish_rate:=20.0
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```
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## AS5600 Register Map
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| Register | Address | Description |
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|---|---|---|
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| RAW_ANGLE | `0x0C`-`0x0D` | 12-bit raw angle (0-4095) |
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| STATUS | `0x0B` | Magnet detect status |
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| AGC | `0x1A` | Automatic gain control |
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## Implementation Notes
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- AS5600 has a **fixed I2C address (0x36)** — cannot be changed. For multiple encoders, each must be on a **separate I2C bus**
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- Uses Linux I2C via `ioctl()` + `linux/i2c-dev.h` — no external library dependency
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- `I2C_SLAVE` address is set once per fd at startup (each fd is dedicated to one bus/encoder)
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- Raw angle read: write register `0x0C`, read 2 bytes → `((buf[0] & 0x0F) << 8) | buf[1]` (12-bit)
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- Angle conversion: `raw * 360.0 / 4096.0` degrees
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- Timer callback iterates all fds and publishes one `EncoderRead` per encoder with `encoder_id` matching the index in `i2c_devices`
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## Raspberry Pi I2C Setup
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The Pi has one hardware I2C bus (`/dev/i2c-1`) by default. For multiple AS5600 encoders, enable extra I2C buses via GPIO bit-banging overlays in `/boot/config.txt`:
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```
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# Extra I2C buses using GPIO pins
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dtoverlay=i2c-gpio,bus=3,i2c_gpio_sda=17,i2c_gpio_scl=27
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dtoverlay=i2c-gpio,bus=4,i2c_gpio_sda=22,i2c_gpio_scl=23
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```
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After reboot, verify with `ls /dev/i2c-*` and `i2cdetect -y <bus>`.
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