# 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)

---

## 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
```

---

## 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

```bash
# 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 |

---

## 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.

```bash
# 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 |

---

## 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) |

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

---

## 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) |

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

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

---

## 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 |

---

## 6. Device Enumeration Notes

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

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