I2C Communication Issues with PCA9685 on Jetson Orin Nano

Issue Overview

Users are experiencing difficulties establishing I2C communication between the Jetson Orin Nano Developer Kit and a PCA9685 servo controller board. The main symptoms include:

• Inability to control servos despite seemingly successful I2C detection
• Inconsistent device addressing (0x40 vs 0x70)
• Errors when attempting to set servo angles or duty cycles
• Differences in I2C bus configuration compared to the original Jetson Nano

These issues are occurring during the initial setup and testing of servo control projects, impacting the ability to develop applications requiring precise motor control.

Possible Causes

1. I2C bus configuration differences: The Jetson Orin Nano has a different I2C bus layout compared to the original Jetson Nano, potentially causing confusion and misconfigurations.

2. Device addressing conflicts: The PCA9685 is not consistently appearing at the expected 0x40 address, which may be due to hardware issues or conflicts with other devices on the I2C bus.

3. Software compatibility: Libraries and code examples developed for the original Jetson Nano may not be fully compatible with the Jetson Orin Nano’s architecture.

4. Hardware connectivity issues: Improper wiring or loose connections between the Jetson Orin Nano and the PCA9685 board could lead to communication failures.

5. Driver or kernel module problems: The necessary I2C drivers or kernel modules may not be properly loaded or configured on the Jetson Orin Nano.

Troubleshooting Steps, Solutions & Fixes

1. Verify I2C bus configuration:

   • Use the correct pinout for the Jetson Orin Nano: https://jetsonhacks.com/nvidia-jetson-orin-nano-gpio-header-pinout/
   • Connect SDA to pin 3 and SCL to pin 5 for I2C Bus 7, or use pins 27 and 28 for I2C Bus 1

2. Check I2C device detection:

   sudo i2cdetect -y -r 7   # For I2C Bus 7
   sudo i2cdetect -y -r 1   # For I2C Bus 1
   

   Verify that the PCA9685 appears at either 0x40 or 0x70

3. Use a logic analyzer to verify proper I2C communication between the Jetson Orin Nano and the PCA9685

4. Implement low-level I2C communication:

   • Obtain the PCA9685 datasheet: https://www.nxp.com/docs/en/data-sheet/PCA9685.pdf
   • Write code to access the chip registers directly, bypassing high-level libraries
   • Test basic functionality like full on, full off, and PWM outputs

5. Update software and libraries:

   • Ensure you’re using the latest JetPack SDK for the Jetson Orin Nano
   • Update Python and relevant libraries (adafruit_servokit, adafruit_pca9685, etc.)

6. Modify I2C bus addressing in Python:
   If unable to use I2C Bus 7, try the following code for I2C Bus 1:

   import board
   import busio
   import adafruit_pca9685
   
   i2c = busio.I2C(board.SCL_1, board.SDA_1)
   pca = adafruit_pca9685.PCA9685(i2c, address=0x70)  # Use 0x70 if 0x40 is not detected
   

7. Implement Device Tree Overlay:

   • Research and apply Jetson Device Tree Overlay to properly configure I2C buses
   • Refer to NVIDIA documentation: https://docs.nvidia.com/jetson/archives/r35.1/DeveloperGuide/text/HR/DeviceTreeOverlay.html

8. Check power supply:
   Ensure the PCA9685 board is receiving adequate and stable power

9. Try alternative I2C libraries:
   If Adafruit libraries are problematic, consider using smbus or other low-level I2C libraries

10. Isolate hardware issues:

    • Test the PCA9685 board with a known working system (e.g., Raspberry Pi or original Jetson Nano)
    • Try multiple PCA9685 boards to rule out faulty hardware

11. Monitor system logs:

    dmesg | grep i2c
    

    Look for any I2C-related errors or warnings

12. Consider using GPIO pins for direct servo control as a temporary workaround while resolving I2C issues

If these steps do not resolve the issue, consider reaching out to NVIDIA developer support or the PCA9685 manufacturer for further assistance. The community is actively working on resolving these compatibility issues, so stay updated with the latest forum discussions and software releases.