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Yet another home/limit switch GRBL problem

Discussion in 'Control Software' started by JammyJulien, Apr 2, 2017.

  1. JammyJulien


    Apr 2, 2017
    Likes Received:
    Hey all,

    I'm hoping for someone to give me some advice. I've build my own CNC machine which works well. Recently I decided to add home and limit switches, but I just cannot get them to work properly.

    I have been googling all morning and completed a lot of testing - but bCNC just brings up a homing alarm as soon as Z axis has homed (It's homed, and moved 5 mm off the homing switch). It doesnt appear the X and Y even tries to move.

    If I move any axis onto their home or limit switches, bCNC gives me limit alarms correctly.

    I have used 47uf capacitors connect to the home switches, which are wired as suggested on sites I have seen (I could try using 330 ohm resistors, but I have seen both used so guessed they are both suitable).

    I'm using GRBL 0.9j.

    As far as testing as gone, Ive set $10=255 and testing the switched. The ? Lim: settings reflect the status of the home and limit switches correctly (they are all wired in parallel). So all off in a normal state - and each switch pair reacts as expected.

    Any advice would be greatly appreciated, I can send pictures or explain the wiring in more detail if required.

    My GRBL settings are :

    Grbl 0.9j ['$' for help]
    $0=10 (step pulse, usec)
    $1=25 (step idle delay, msec)
    $2=0 (step port invert mask:00000000)
    $3=0 (dir port invert mask:00000000)
    $4=0 (step enable invert, bool)
    $5=0 (limit pins invert, bool)
    $6=0 (probe pin invert, bool)
    $10=255 (status report mask:11111111)
    $11=0.010 (junction deviation, mm)
    $12=0.002 (arc tolerance, mm)
    $13=0 (report inches, bool)
    $20=0 (soft limits, bool)
    $21=1 (hard limits, bool)
    $22=1 (homing cycle, bool)
    $23=3 (homing dir invert mask:00000011)
    $24=25.000 (homing feed, mm/min)
    $25=300.000 (homing seek, mm/min)
    $26=250 (homing debounce, msec)
    $27=3.000 (homing pull-off, mm)
    $100=50.000 (x, step/mm)
    $101=400.000 (y, step/mm)
    $102=400.000 (z, step/mm)
    $110=1900.000 (x max rate, mm/min)
    $111=300.000 (y max rate, mm/min)
    $112=300.000 (z max rate, mm/min)
    $120=100.000 (x accel, mm/sec^2)
    $121=10.000 (y accel, mm/sec^2)
    $122=10.000 (z accel, mm/sec^2)
    $130=500.000 (x max travel, mm)
    $131=500.000 (y max travel, mm)
    $132=140.000 (z max travel, mm)

    Thanks all,

  2. JammyJulien


    Apr 2, 2017
    Likes Received:
    I've resolved this problem by creating a circuit as per attached picture.

    Attached Files:

    Rick 2.0 likes this.
  3. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder Resident Builder

    Aug 6, 2013
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    MaryD likes this.
  4. Rodm

    Rodm Well-Known

    Jan 3, 2017
    Likes Received:
    David the swarfer likes this.

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