INA3221 External Power Monitor for Jetson Orin Nano

Add a second INA3221 power monitor to your Jetson Orin Nano for battery/charger power monitoring or custom power rail monitoring.

📋 Overview

The Jetson Orin Nano has a built-in INA3221 (address 0x40) monitoring system power. This project adds a second INA3221 (address 0x41) to monitor three additional power rails - perfect for battery/charger monitoring or custom applications.

Use Case: Monitor battery power state - battery input, DC input to Jetson, and charge port on the three channels.

What You Get

• ✅ 6 total power monitoring channels (3 built-in + 3 external)
• ✅ Simple installation - one script to set up
• ✅ Persistent - survives reboots
• ✅ Easy to remove - no system file modifications
• ✅ Well documented - comprehensive guides for all aspects

🛠 Hardware Requirements

• Jetson Orin Nano Developer Kit
• External INA3221 power monitor module
• I2C connections to I2C-1 bus (GPIO 27/28)
• Address configuration: A0=HIGH, A1=LOW (address 0x41)
• Shunt resistors (500mΩ recommended for < 1A loads)

🚀 Quick Start

# Clone repository
git clone https://github.com/NeaveEng/ina3221-external.git
cd ina3221-external

# Install
sudo ./setup_ina3221.sh

# Reboot to test persistence
sudo reboot

# Read sensors
sudo ./read_ina3221_sensors.sh

That's it! Your external INA3221 is now monitoring your custom power rails.

📁 Documentation

This project includes comprehensive documentation split by topic:

📖 Guides

• USAGE.md - How to read sensors and integrate with your applications
• CALIBRATION.md - Shunt resistor calibration for accurate measurements
• TROUBLESHOOTING.md - Solutions to common issues
• PERSISTENCE_GUIDE.md - How persistence works and testing
• HOW_IT_WORKS.md - Technical deep-dive on I2C device creation
• TECHNICAL.md - Hardware specs, kernel details, and advanced topics

🔧 Scripts

Script	Purpose
setup_ina3221.sh	Main installation - creates systemd service
read_ina3221_sensors.sh	Read all INA3221 sensors with formatted output
calibrate_ina3221.sh	Calibrate shunt resistors for accurate readings
test_persistence.sh	Test that device persists across reboots

📊 Channel Configuration

Built-in INA3221 (0x40)

Channel	Monitors
0	VDD_IN - Main input voltage
1	VDD_CPU_GPU_CV - CPU/GPU power
2	VDD_SOC - SoC power

External INA3221 (0x41)

Channel	Your Use Case
0	Custom (e.g., DC input to Jetson)
1	Custom (e.g., Charge port)
2	Custom (e.g., Battery input)

📖 Common Tasks

Read Sensors

sudo ./read_ina3221_sensors.sh

Change Shunt Resistor Values

See CALIBRATION.md for detailed instructions.

# Quick method for 100mΩ resistors:
nano calibrate_ina3221.sh  # Change SHUNT_VALUE=100000
sudo ./calibrate_ina3221.sh

Check Service Status

sudo systemctl status ina3221-external.service

Uninstall

sudo systemctl disable --now ina3221-external.service
sudo rm /etc/systemd/system/ina3221-external.service
sudo systemctl daemon-reload
echo 0x41 | sudo tee /sys/bus/i2c/devices/i2c-1/delete_device

🔍 How It Works

This project uses a systemd service to create the I2C device at boot (not device tree overlays, which don't work reliably on Jetson).

The service:

1. Creates I2C device at address 0x41
2. Kernel driver (ina3221) automatically binds
3. hwmon interface appears at /sys/class/hwmon/hwmonX/
4. Shunt resistors are calibrated to 500mΩ (configurable)

For technical details, see HOW_IT_WORKS.md and TECHNICAL.md.

⚡ Sample Output

=== INA3221 Power Monitor Reading ===

--- Built-in INA3221 (Address: 0x40) ---
  Channel 0 (VDD_IN):
    Voltage: 5104 mV
    Current: 912 mA
    Power: 4654 mW

--- External INA3221 (Address: 0x41) ---
  Channel 0 (CUSTOM_RAIL_1):
    Voltage: 11776 mV
    Current: 160 mA
    Power: 1884 mW
  Channel 1 (CUSTOM_RAIL_2):
    Voltage: 11968 mV
    Current: -178 mA      # Negative = supplying power
    Power: -2130 mW
  Channel 2 (CUSTOM_RAIL_3):
    Voltage: 11864 mV
    Current: 17 mA
    Power: 201 mW

🐛 Troubleshooting

Having issues? See TROUBLESHOOTING.md for solutions to:

• Device not detected
• Service fails to start
• Incorrect readings
• Permission errors
• And more...

Quick diagnostic:

# Check I2C bus
sudo i2cdetect -y 1

# Check service logs
sudo journalctl -u ina3221-external.service -n 50

# Check device exists
ls /sys/bus/i2c/devices/1-0041/

🤝 Contributing

Contributions welcome! Areas for improvement:

• Support for other INA32xx variants
• Python library for easy integration
• Automated testing scripts
• Additional use case examples

⚠️ Important Notes

1. Shunt Resistor Power Rating: Ensure your shunt resistors can handle the power dissipation (P = I² × R)
2. Voltage Limits: INA3221 measures 0-26V bus voltage, ±163.8mV shunt voltage
3. I2C Address: Verify A0=HIGH, A1=LOW for address 0x41
4. No Boot File Changes: This method doesn't modify DTB or boot configuration (safe!)

📄 License

MIT License - See LICENSE file.

Free for commercial and personal use.

🤖 AI Development

This project was developed with AI assistance. All code has been:

• Validated against official documentation
• Tested on real Jetson Orin Nano hardware
• Verified for safety and reliability

Key references:

• NVIDIA Jetson Linux Developer Guide
• INA3221 Datasheet
• Linux hwmon Documentation

---

Need help? Check the documentation guides above or open an issue on GitHub.