Feedback pin issue on Parallax 900-00360 servo

[00.salon.flyer]

I am able to continuously spin the Parallax 900-00360 servo using the required 50Hz control signal at 3.3VDC logic level, with the servo powered by a 6VDC supply. The ground (GND) of the 6V supply is correctly connected to the Raspberry Pi 5’s ground.

When the feedback pin is not connected to any load, the servo provides a 3.3V PWM feedback signal. However, when I connect this feedback pin to an input pin on the Raspberry Pi 5, the feedback signal level drops to 2V. Furthermore, when I connect the feedback signal through only a 10K resistor to ground, the signal drops to less than 1.2V.

These signal levels were measured with an oscilloscope. I could not find any information about the output impedance of the feedback signal in the servo’s datasheet, but these voltage drops don’t seem right. Am I missing something that could be causing this issue?

Thanks,
Tom

[APDahlen]

Hello @00.salon.flyer,

With 75% confidence, I’m led to believe that this is normal operation for the Parallax 900-00360 servo.

This Adafruit video identifies the Hall sensor as a type AS5600-ASOM.

New Products 9/27/2017

At this point we make an assumption. If I were to design the product, I would guard against inadvertently connection of the feedback signal to 5 VDC. We therefor assume a current limiting feedback resistor is installed.

Knowing that the design max for the AS5600 is 0.5 mA, we can expect a series resistor of approximately 10 kΩ. This assumption is supported by your data.

Thoughts?

Best wishes,

APDahlen

[00.salon.flyer]

Thank you, APDahlen. You are correct. Using the RPi 5 with the gpiozero class with DigitalInputDevice(feedback_pin, pull_up=None, active_state=True) is required. The input logic level is now correct.