226 lines
9.6 KiB
Markdown
226 lines
9.6 KiB
Markdown
# Robot Controller
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ROS 2 nodes for the Yahboom Raspbot V2 — differential-drive motor control, pan/tilt camera orientation, and ultrasonic range sensing.
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All three nodes share the same I²C bus. The Linux kernel serialises individual transactions, so they run as separate processes without additional locking.
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---
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## Motor controller
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```
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┌───────────────────────────────────┐
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│ MotorControllerNode │
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│ │
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/cmd_vel ──────────>│ Twist → differential kinematics │
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(geometry_msgs/Twist)│ left = linear − (angular × wb/2)│
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│ right = linear + (angular × wb/2)│
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│ │
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/wheel_speeds ──────>│ Direct per-wheel override │
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(Float32MultiArray │ [FL, FR, RL, RR] │
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4 × float32) │ │
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│ ▼ │
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│ raspbot_v2_interface │
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│ I²C bus 1, addr 0x2B │
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│ ▼ │
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│ /dev/i2c-1 ─────────> Motors │
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│ │
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/current_wheel_speeds│<─ telemetry @ 10 Hz │
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(Float32MultiArray) │ [FL, FR, RL, RR] │
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└───────────────────────────────────┘
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```
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### Topics
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| Topic | Direction | Type | Description |
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|---|---|---|---|
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| `/cmd_vel` | Subscribed | `geometry_msgs/Twist` | Velocity command — `linear.x` (m/s) and `angular.z` (rad/s) |
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| `/wheel_speeds` | Subscribed | `std_msgs/Float32MultiArray` | Direct per-wheel speed override `[FL, FR, RL, RR]` in library units (0–255) |
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| `/current_wheel_speeds` | Published | `std_msgs/Float32MultiArray` | Current wheel speeds read from hardware, published at 10 Hz |
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### Parameters
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| Parameter | Default | Description |
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|---|---|---|
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| `wheel_base` | `0.3` | Distance between left and right wheels in metres |
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| `max_speed` | `1.0` | Maximum motor speed in library units |
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### Sending velocity commands
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```bash
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# Drive forward at 0.2 m/s
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ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
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"{linear: {x: 0.02}, angular: {z: 0.0}}"
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# Turn on the spot
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ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
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"{linear: {x: 0.0}, angular: {z: 0.5}}"
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# Stop
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ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
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"{linear: {x: 0.0}, angular: {z: 0.0}}"
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```
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---
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## Camera orientation controller
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```
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┌──────────────────────────────────────┐
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│ CameraOrientationNode │
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│ │
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/joint_command ────────>│ JointState (names: pan, tilt) │
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(sensor_msgs/ │ position in radians │
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JointState) │ │
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│ pan → servo 1 (0°–180°) │
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│ tilt → servo 2 (0°–110°) │
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│ │
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│ ▼ │
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│ raspbot_v2_interface │
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│ I²C bus 1, addr 0x2B │
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│ ▼ │
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│ /dev/i2c-1 ──────> Pan/tilt servos │
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│ │
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/joint_states <────────│ current angles @ 10 Hz │
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(sensor_msgs/ │ position in radians │
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JointState) │ │
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└──────────────────────────────────────┘
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```
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### Topics
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| Topic | Direction | Type | Description |
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|---|---|---|---|
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| `/joint_command` | Subscribed | `sensor_msgs/JointState` | Commanded pan/tilt angles. Joint names `"pan"` and `"tilt"`, positions in **radians**. Unknown joint names are ignored. |
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| `/joint_states` | Published | `sensor_msgs/JointState` | Current angles reflected from the last command, published at 10 Hz |
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### Parameters
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| Parameter | Default | Description |
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|---|---|---|
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| `pan_servo_id` | `1` | Raspbot servo channel for pan |
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| `tilt_servo_id` | `2` | Raspbot servo channel for tilt |
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| `pan_min_deg` | `0.0` | Pan lower limit (degrees) |
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| `pan_max_deg` | `180.0` | Pan upper limit (degrees) |
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| `tilt_min_deg` | `0.0` | Tilt lower limit (degrees) |
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| `tilt_max_deg` | `110.0` | Tilt upper limit (degrees) — hardware cap |
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| `pan_center_deg` | `90.0` | Startup and shutdown park position for pan |
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| `tilt_center_deg` | `60.0` | Startup and shutdown park position for tilt |
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| `state_rate_hz` | `10.0` | `~/joint_states` publish rate |
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### Hardware interface
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The node drives the pan and tilt servos over **I²C bus 1** (device address `0x2B`). The same `/dev/i2c-1` device used by the motor controller is sufficient — no additional device node is required.
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### Commanding the camera
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Pan to centre (90°) and tilt to 30°:
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```bash
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ros2 topic pub --once /joint_command sensor_msgs/msg/JointState \
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"{name: ['pan', 'tilt'], position: [1.5708, 0.5236]}"
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```
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A single axis can be commanded by omitting the other joint name:
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```bash
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# Pan only
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ros2 topic pub --once /joint_command sensor_msgs/msg/JointState \
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"{name: ['pan'], position: [0.0]}"
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```
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---
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## Ultrasonic range sensor
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```
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┌──────────────────────────────────────┐
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│ UltrasonicNode │
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│ │
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│ Sensor off when no subscribers │
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│ Sensor on when subscribers > 0 │
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│ 1 s warm-up after power-on │
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│ │
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│ ▼ │
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│ raspbot_v2_interface │
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│ I²C bus 1, addr 0x2B │
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│ ▼ │
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│ /dev/i2c-1 ──────> HC-SR04 sensor │
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│ │
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/ultrasonic/range <────│ Range @ configurable rate │
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(sensor_msgs/Range) │ radiation_type = ULTRASOUND │
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│ range in metres (REP-117) │
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└──────────────────────────────────────┘
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```
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### Topics
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| Topic | Direction | Type | Description |
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| `/ultrasonic/range` | Published | `sensor_msgs/Range` | Distance in metres. `+inf` when beyond max range, `-inf` when closer than min range (REP-117). Only published while subscribers are connected. |
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### Parameters
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| Parameter | Default | Description |
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| `publish_rate_hz` | `10.0` | Sensor poll and publish rate |
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| `frame_id` | `'ultrasonic'` | `header.frame_id` on published messages |
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| `min_range_m` | `0.02` | Minimum valid range in metres |
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| `max_range_m` | `4.0` | Maximum valid range in metres |
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| `field_of_view` | `0.2618` | Sensor cone width in radians (~15°) |
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| `warmup_s` | `1.0` | Seconds to wait after powering the sensor on before publishing |
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### Verifying range readings
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```bash
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ros2 topic echo /ultrasonic/range
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```
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The sensor activates automatically when a subscriber connects and deactivates when it disconnects.
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---
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## Launch arguments
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Launch arguments can be appended when running the container manually:
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```bash
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docker run --rm \
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--network=host \
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--device /dev/i2c-1 \
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--env ROS_DOMAIN_ID=0 \
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raspbot_v2:latest \
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ros2 launch raspbot_v2 robot.launch.py \
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wheel_base:=0.25 max_speed:=0.8 tilt_center_deg:=45.0
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```
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| Argument | Default | Description |
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| `wheel_base` | `0.3` | Distance between left and right wheels (m) |
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| `max_speed` | `1.0` | Maximum motor speed in library units |
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| `pan_center_deg` | `90.0` | Pan angle at startup and shutdown (degrees) |
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| `tilt_center_deg` | `60.0` | Tilt angle at startup and shutdown (degrees) |
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| `ultrasonic_rate_hz` | `10.0` | Ultrasonic sensor publish rate (Hz) |
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---
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## Project layout
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```
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robot/
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├── Dockerfile # Two-stage build: colcon compile → clean runtime image
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├── src/
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│ └── raspbot_v2/
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│ ├── package.xml
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│ ├── setup.py
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│ ├── launch/
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│ │ └── robot.launch.py # Starts all three nodes together
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│ └── raspbot_v2/
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│ ├── motor_controller_node.py
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│ ├── camera_orientation_node.py
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│ └── ultrasonic_node.py
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└── raspbot_v2_interface/ # Vendored Yahboom hardware library
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└── Raspbot_Lib/
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└── Raspbot_Lib.py # I²C driver (smbus, bus 1, addr 0x2B)
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```
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