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IndustryArena Forum > OpenSource CNC Design Center > Arduino > GRBL touch probe noise problem???
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  1. #1
    Join Date
    Sep 2013
    Posts
    9

    GRBL touch probe noise problem???

    Hi!

    I've recently finished to make a mini CNC mill for PCB routing with GRBL 1.1f firmware version. Last week, I've installed an aluminium block on it for automated Z zero tool lenght. The block has two wire, one corresponding to the aluminium block (A5 probe pin in Arduino) and the other end, to GND in Arduino and motor chasis.

    I've tested continuity between the tool and motor chasis and all is ok! I tested the probe and all works well.

    The problem comes when I send M3 command to activate the 12V DC motor spindle throught the rele. All 3 steppers begin to rotate, with any signal sended by me. If I disconnect the GND wire on the motor chasis, all works fine.

    My question is? Must I disconnect every time I use the probe the GND wire attached to motor chasis?
    Is a way to leave the wire attached to DC motor chasis without these steppers movements? Must I connect something between A5 and GND on Arduino??

    I hope you can help me with this. Thanks in advance!!

  2. #2
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL touch probe noise problem???

    The A5 from the arduino must be connected to the touch plate. The GND from the arduino must be connected to the chassis as close as possibly to the spindle motor. By this, the spindle motors (chassis) ground current, will try to flow through the arduino GND line, resulting in noise. To avoid this, an easier (lower resistance) current path has to be made, a thick ground wire, connected to the motor chassis (not the paint, use toothed washer) and a central ground point.
    This is not GRBL related, you will have this on every controller.

    You should use a central ground point (star configuration). This ground is not a safety ground but a shielding ground be sure to use thick ground wires.

    All your equipment should have only one ground wire. If there are 2 ground wires, current will flow through these ground wires resulting in noise.

    Keep the low voltage signals like probe, step, dir, etc far away from the high voltage/power lines like A+, A-, Supply.

    If possible, shield all wires and connect those shields to the ground line on one side only.

    Connect the GRBL low voltage signals shielding on the arduino side.

    Use only one Wall Outlet that go's to one distribution box to power your equipment.

    Disconnecting the motor GND wire could destroy the arduino and even the connected PC!!!!



    Let me know the results,

    Huub

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