I'm in the process of calibrating servos while constructing a new hobbyist robot arm. When testing the base rotation servo I noticed some unexpected noise in the PWM signal while the servo is in motion. There is no noise in the PWM signal when the servo is stationary. What causes the PWM noise? Is it likely to be significant? If so how would I filter it? The motion behaviour of the servo is exactly as expected, so the likely answer I'm expecting is to just ignore it, but I wanted to learn more about what I am seeing.
The equipment in use is:
- Arduino Uno as test MCU, powered by USB connection.
- PCA9685 I2C PWM controller with a 470$\mu$F 16V electrolytic filter capacitor
- an inline breakout in the servo connection for multimeter and oscilloscope connection
- external bench power supply 6V limited to 2A
- only one servo is connected to PCA9685 port 0
- the servo is a GoBilda 2000-0025-0002
Update: Link to video of oscilloscope trace (as per the question description - no bypass capacitor between PWM signal and ground).