Triggers for bed leveling



  • I want to use 2 microswitches to level my bed. I would attach one switch to the left of the X carriage and one to the right. The X carriage would move to the left edge of the glass and lower until it activates the right switch and report the Z height. It would then move right of the glass and use the left switch to measure the Z height. It would do this front and back. I would then end up with a set of 4 readings that i can adjust to level the bed.

    Would these work in a routine to do that?

    M581: Configure external trigger
    M582: Check external trigger

    Basically what the BCN guys do on the sigma

    https://youtu.be/SZ232J-dnkA


  • administrators

    If you use NC switches and wire them in series, you can use them just like a single switch Z probe.



  • Ok fair point. So if i have multiple Z switches how can i use those switches to read the Z height against 0. For example my printer starts with a Z height of 0. Then i move along the bed edge and probe with the switch but as soon as the switch hits the bed it reports 0 Z height.

    G1 Z-200 S1 F100 will stop fine when it hits the bed but this command sets the height to 0?. How do i read the actual height? If i can manage to read the height i can then do the simple math for adjustment.

    Thanks for your help!



  • When you say "How do I read the actual height?", is your intent to determine the Z probe offset from 0?



  • Sounds like he needs to make a macro to use G30: http://reprap.org/wiki/G-code#G30:_Single_Z-Probe



  • Thanks guys. I won't defend myself, I was thinking G30 is strictly for an IR probe…



  • Just to confirm I can use P5 on the M558 command and use the pins on the IR probe connector for the switches is series instead of going the E0 route?


  • administrators

    I normally recommend using E0 for a switch-type Z probe because it has filtering, an indicator LED and a lower value pullup resistor. However, using the GND and IN pins of the Z probe connector will probably work OK with NC switches.



  • Thanks for all your help guys. I've now got a working bed leveling system. I'm just starting to write the Javascript now that reads the 4 point output and calculates how many turns in what direction of what knob to turn to level the bed 🙂

    Thanks again!


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