PCA9685 Servo Driver Not Working on Jetson Orin Nano

Robotics & Edge Computing Jetson Systems Jetson Orin Nano
1

I cannot get servos to move using the PCA9685 servo driver on my Jetson Orin Nano, despite successful I2C communication and proper register configuration. The servo works fine when tested on Arduino, so it isn’t broken.

What Works:

  • PCA9685 detected on I2C bus 7 at address 0x40
  • sudo i2cdetect -y -r 7 shows device at 0x40
  • Can read/write PCA9685 registers successfully via smbus2
  • Register values verify correctly (MODE1, MODE2, PRESCALE, channel PWM registers)
  • Servo confirmed working on Arduino
  • Power verified: 3.7V measured at PCA9685 V+ terminal
  • Common ground established between battery, PCA9685, and Jetson
  • Permissions all set (groups includes both gpio and i2c)

What Doesn’t Work:

  • Servo does not move at all (no sound, no twitch, no resistance)
  • Tested with two different servos - neither works
  • Both smbus2 and Adafruit ServoKit (via gpio) library produce no movement

Here’s my setup:

  • Board: Jetson Orin Nano Developer Kit “Super” variant
  • JetPack Version: 6.2.1
  • OS: Ubuntu (based on JetPack 6.2.1)
  • Python: 3.10
  • Servo Driver: Adafruit PCA9685 (genuine board) on pins 3 and 5 on the Jetson
  • Servo: MG90S micro servo (tested and confirmed working on Arduino)
  • Power: Single 3.7V LiPo battery (9800mAh) connected to PCA9685 V+ terminal
  • I2C Bus: PCA9685 detected on bus 7 at address 0x40

The code runs with no errors but the servo does not move at all.
Here’s the script I’ve tested (+ some variants of this structure):

from smbus2 import SMBus
import time

bus = SMBus(7)
addr = 0x40

# Configure MODE2 (OUTDRV bit for totem-pole outputs)
bus.write_byte_data(addr, 0x01, 0x04)
time.sleep(0.01)

# Initialize for 50Hz
bus.write_byte_data(addr, 0x00, 0x10)  # Sleep
bus.write_byte_data(addr, 0xFE, 0x79)  # Prescale for 50Hz
bus.write_byte_data(addr, 0x00, 0xA0)  # Wake + restart
time.sleep(0.01)

# Set channel 0 to 90 degrees (~1500us pulse)
bus.write_byte_data(addr, 0x06, 0x00)  # LED0_ON_L
bus.write_byte_data(addr, 0x07, 0x00)  # LED0_ON_H
bus.write_byte_data(addr, 0x08, 0x33)  # LED0_OFF_L (307 ticks)
bus.write_byte_data(addr, 0x09, 0x01)  # LED0_OFF_H

time.sleep(2)
bus.close()

And for the ServoKit library (+ variants of this structure):

from adafruit_servokit import ServoKit
import board
import busio

i2c = busio.I2C(board.SCL, board.SDA)
kit = ServoKit(channels=16, i2c=i2c)

kit.servo[0].angle = 90
2

A few extra information:

$ cat /proc/device-tree/model
NVIDIA Jetson Orin Nano Engineering Reference Developer Kit Super

$ cat /proc/device-tree/compatible
nvidia,p3768-0000+p3767-0005-supernvidia,p3767-0005nvidia,tegra234

5

Do you config the i2s pin function by jetson-io?

Thanks

6

I did! I configured and rebooted

7

Could you probe the output signal to confirm.

Thanks

8

Just did! turns out my pca9685 was broken (what are the chances!!)
I switched it for a new one and everything’s working! Thank you so much!

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