Servo control from Z_Probe_Mod pin for probe.



  • Hello,

    I designed this ZProbe that I am using since then with good reliability and results. It uses a simple 9g servo for deploy and retract of the probe and a simple optical endstop to trigger it.

    I did not test it yet but by searching and reading about I am confident that both, servo and endstop, can be powered by 3.3v. I use four wires for my probe: +v, ground, servo signal and probe signal that I plan to connect directly to the dedicated probe connector of the Duet Ethernet (not delivered yet).

    My questions are:

    Is it possible to control the servo from the "Z_Probe_Mod" pin?
    There is enough current to power a small 9g servo from the +3.3v pin? Is it risky to test it?

    Thank you very much!


  • administrators

    1. The Z probe MOD pin cannot be used to control a servo because it is not a PWM- or timer-capable pin. See https://duet3d.dozuki.com/Wiki/Using_servos_and_controlling_unused_IO_pins for the pins you can use.

    2. It would be very risky to run a servo from the 3.3V supply, not only because of the current draw but also because of the energy that servos feed back into the power supply when decelerating. However, many 5V servos will work if they are powered from 5V but given a 3.3V control signal.



  • Thank you very much!!

    Then I'll connect the endstop wires to the Z endstop plug and wire the servo to the correct 5v supply and signal pin.

    I would prefer a nice and clean one plug solution though 😄

    Would you recommend an external 5V supply due to the servo load (My Arduino could not handle it) or the 5v regulator from the Duet can handle the current of one 9g servo?


  • administrators

    By "9g servo", do you mean the servo weighs 9 grammes?

    The 5V regulator on the Duet can easily provide enough current for a small servo. The servo I test with weights around 50g. The Duet powers that easily enough, but that servo delivers a big kick into the 5V power rail when it stops.



  • Not sure if the 9g refers to the weight or torque of these small servos. But it is a "SG90 tower pro" micro servo that people refer to them as 9g servos.

    Is there any recommendations to protect the 5v rail from the big kick when it stops?

    Thank you very much!


  • administrators

    @brunofporto said in Servo control from Z_Probe_Mod pin for probe.:

    Is there any recommendations to protect the 5v rail from the big kick when it stops?

    Yes, connect a 220uF capacitor across the 5V supply to the servo.



  • Thank you! Will do.


 

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