Makerbot Limit Switch Issue



  • Hi All,

    I've just realised that these limit switches do not go open circuit but raise the circuit resistance to 10kOhm. Is there a way to adjust the config file to force the hardware to consider a higher voltage as an open active high switch?

    I've connected to the VCC can Sig pins which are 1 and 3 counting from the long edge side with the switch on it. Measuring resistance across the GND (pin2) and SIG gives a normally low response which I'd rather avoid. The LEDs on the board dim when the limit switch is pressed but do not extinguish. There is no obvious difference between the lights. Using M119 I can see the z end stop behaving as expected. Press the switch and the response is at max limit. None of the other switches work. Pulling the wire off the switch does prompt an at limit response for X and Y axis. When I move the lead from the z switch to the x switch the x switch reports at limit as expected. If anything the wires for the z limit are the shortest on the board, and the measured resistance is fractionally lower, although inside the margin of error. that'd be expected for dodgy probe to terminal contacts.

    Summary:

    • Can a specified resistance/voltage be considered an at limit signal? This would also improve physical error handling as open circuit would be a fault rather than an axis on a switch.
    • Are X/Y limit switch triggers coded different to the Z axis limit trigger? There is no z-probe specified in the config at the moment.

    Failing all this I will have to use active low until I can either modify the board or replace the switches.

    Thanks!



  • Missing information:

    Duet 0.6 running 1.19

    Found this thread which appears to discuss the same issue and confirms that the Duet usually needs the lights to fully extinguish. They used the same switches and duet.

    Odd that the z switch works but not the x/y.

    Any chance of having the resistance for triggered rather than open circuit as an option?



  • If you don't want to buy new switches, you could hack them to work.



  • Yeah, I'm going to try and remove the surface mount components. The LED and resistor are as expected but there is also a resistor-capacitor in there which I'm presuming is for de-bouncing the switch.

    The behaviour difference between the X/Y and Z axis is odd though.


  • administrators

    Those switches will probably work with a Duet without modification. Just make sure you connect them correctly, because the 3 pins are in a different order on the Duet (Vcc aka 3.3V is in the middle on the Duet endstop connectors).



  • Yeah, they didn't until I took the components off the board. I wanted to avoid normally open. The 10kOhm appears to be right on the limit of what the duet decides is off. Strip the components off and you can use normally open or closed.


 

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