saltylab-firmware/jetson/docs/pinout.md

Jetson Nano — GPIO / I2C / UART Pinout Reference

Self-Balancing Robot: STM32F722 Bridge + RealSense D435i + RPLIDAR A1M8

Last updated: 2026-02-28 JetPack version: 4.6 (L4T R32.6.1)

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40-Pin Header Overview

The Jetson Nano 40-pin header is physically compatible with Raspberry Pi HATs. Pin numbering below follows physical board pin (1–40) and the Jetson GPIO BCM-equivalent name.

 3.3V  [ 1] [ 2] 5V
SDA1  [ 3] [ 4] 5V         ← I2C SDA (i2c-1)
SCL1  [ 5] [ 6] GND        ← I2C SCL (i2c-1)
 GPIO [ 7] [ 8] TXD0       ← UART TX (ttyTHS1)
  GND [ 9] [10] RXD0       ← UART RX (ttyTHS1)
 GPIO [11] [12] GPIO
 GPIO [13] [14] GND
 GPIO [15] [16] GPIO
 3.3V [17] [18] GPIO
 MOSI [19] [20] GND        ← SPI0 MOSI
 MISO [21] [22] GPIO       ← SPI0 MISO
 SCLK [23] [24] CE0        ← SPI0 CLK / CS0
  GND [25] [26] CE1        ← SPI0 CS1
  ID_SD[27] [28] ID_SC     ← I2C ID EEPROM (reserved)
 GPIO [29] [30] GND
 GPIO [31] [32] GPIO
 GPIO [33] [34] GND
 GPIO [35] [36] GPIO
 GPIO [37] [38] GPIO
  GND [39] [40] GPIO

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1. STM32F722 Bridge (UART)

The STM32 acts as a real-time motor + IMU controller. Communication to Jetson is via USB CDC serial (primary) with hardware UART as fallback.

USB CDC (Primary — Recommended)

Connection	Detail
Interface	USB Micro-B on STM32 dev board → USB-A on Jetson
Device node	/dev/ttyACM0 or /dev/ttyUSB1
Baud rate	921600 (configured in STM32 firmware)
Protocol	Custom binary framing (see src/comm/)
Power	Powered via Jetson USB 5V (500mA max from host)

Hardware UART (Fallback)

Jetson Pin	Signal	STM32 Pin	Notes
Pin 8 (TXD0)	TX →	PA10 (UART1 RX)	Cross-connect TX→RX
Pin 10 (RXD0)	RX ←	PA9 (UART1 TX)	Cross-connect RX→TX
Pin 6 (GND)	GND	GND	Common ground required

Jetson device node: /dev/ttyTHS1 Baud rate: 921600, 8N1 Voltage level: 3.3V — STM32F722 is 3.3V tolerant; Jetson GPIO is 3.3V Do NOT use 5V — Jetson GPIO max is 3.3V

# Verify UART on Jetson
ls /dev/ttyTHS1
# Check permissions (add user to dialout group)
sudo usermod -aG dialout $USER
# Quick loopback test (connect TX→RX)
picocom -b 921600 /dev/ttyTHS1

ROS2 topic mapping (STM32 bridge node):

ROS2 Topic	Direction	Content
/stm32/imu_raw	STM32→Jetson	IMU data (accel, gyro) at 500Hz
/stm32/motor_state	STM32→Jetson	Motor RPM, current, temperature
/cmd_vel	Jetson→STM32	Velocity commands (m/s, rad/s)
/stm32/estop	Jetson→STM32	Emergency stop signal

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2. RealSense D435i (USB3)

The D435i provides RGB-D (depth + color) and IMU (accelerometer + gyroscope).

Connection

Parameter	Value
Interface	USB 3.1 Gen 1 (USB-A on Jetson)
Device node	/dev/bus/usb/... (udev-managed)
USB PID:VID	0x8086:0x0b3a (D435i)
Power draw	~1.5W active, 3.5W peak during init
Cable	USB 3.1 — use short cable ≤1m for stability

Note: The Jetson Nano has 4× USB-A ports — use a USB3 port (blue) for D435i.

# Verify detection
lsusb | grep Intel
# Expected: Bus 002 Device 003: ID 8086:0b3a Intel Corp. Intel RealSense D435i

# Install udev rules (required for non-root access)
sudo cp /etc/udev/rules.d/99-realsense-libusb.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules && sudo udevadm trigger

# Test with realsense-viewer (if installed)
realsense-viewer

ROS2 topics published:

Topic	Type	Rate
/camera/color/image_raw	sensor_msgs/Image	30Hz
/camera/depth/image_rect_raw	sensor_msgs/Image	30Hz
/camera/aligned_depth_to_color/image_raw	sensor_msgs/Image	30Hz
/camera/imu	sensor_msgs/Imu	400Hz
/camera/color/camera_info	sensor_msgs/CameraInfo	30Hz

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3. RPLIDAR A1M8 (UART via USB adapter)

The A1M8 uses a CP2102/CH340 USB-UART adapter (included in kit).

Connection

Parameter	Value
Interface	USB Micro-B (via included USB-UART adapter)
Device node	/dev/ttyUSB0 (first USB-UART device)
Baud rate	115200
Power draw	~2.6W motor on, 0.4W idle
Motor control	DTR line (handled by rplidar_ros driver)

# Verify detection
ls /dev/ttyUSB*
# Expected: /dev/ttyUSB0

# Set permissions
sudo usermod -aG dialout $USER

# Test — should output scan data
ros2 launch rplidar_ros rplidar_a1_launch.py serial_port:=/dev/ttyUSB0

ROS2 topics published:

Topic	Type	Rate
/scan	sensor_msgs/LaserScan	10Hz

udev rule (set consistent device name):

# /etc/udev/rules.d/99-rplidar.rules
KERNEL=="ttyUSB*", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", \
  SYMLINK+="rplidar", MODE="0666"

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4. I2C Bus (i2c-1) — Pin 3 / Pin 5

Available for future peripherals (IMU breakout, OLED display, etc.).

Parameter	Value
Jetson I2C bus	i2c-1 (pins 3 = SDA, 5 = SCL)
Voltage	3.3V pull-up
Max clock	400kHz (Fast Mode)
Current source	Jetson 3.3V rail (max ~500mA shared)

# Scan i2c-1 bus
i2cdetect -y -r 1

Note: i2c-0 (pins 27/28) is reserved for EEPROM ID — do not use.

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5. GPIO Summary Table

Physical Pin	Jetson GPIO	Voltage	Current Used For
3	SDA1	3.3V	I2C data (i2c-1)
5	SCL1	3.3V	I2C clock (i2c-1)
8	TXD0	3.3V	UART TX → STM32 (fallback)
10	RXD0	3.3V	UART RX ← STM32 (fallback)
USB-A (×4)	—	5V	D435i, RPLIDAR adapter, STM32 USB

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6. Device Enumeration Notes

USB devices may enumerate differently across reboots. Use udev rules for stable names:

# /etc/udev/rules.d/99-saltybot.rules

# RPLIDAR A1M8 (SiliconLabs CP2102)
KERNEL=="ttyUSB*", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", \
  SYMLINK+="rplidar", MODE="0666"

# STM32 USB CDC (STMicroelectronics)
KERNEL=="ttyACM*", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="5740", \
  SYMLINK+="stm32-bridge", MODE="0666"

Apply rules:

sudo cp docs/99-saltybot.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules && sudo udevadm trigger