Wiring limit switches

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  • January 23, 2015 at 6:03 pm #7306
    Jim
    Member

    Ok, I feel stupid, but how do I actually wire a limit switch. Sure, one wire goes to the proper limit pin, but where does the other wire go? Does it go to Ground or to 3.3V?

    The Wiki page Homing and Limits Setup and Troubleshooting does not actually describe wiring the switches.

    I don’t want to wire something up wrong and blow my board. Further, I was following a thread on limit switches on GrblShield and that schematic calls for wiring up a switch that can be both NO and NC and wiring up the input pin, GND, and the voltage (IOREF). Again, before I do something that I shouldn’t, I want to ask the experts.
    http://www.shapeoko.com/forum/viewtopic.php?f=26&t=4046&start=16

    Thanks

    • This topic was modified 9 years, 10 months ago by Jim.
    January 23, 2015 at 10:57 pm #7308
    cmcgrath5035
    Moderator

    Jim
    Be somewhat careful bouncing between GRBL and tinyG docs, Uno/Gshield is 5V logic, tinyG is 3.3V logic.

    So you are wiring the switches between 3.3V and ground.
    A NC switch will hold the port low normally, it will go high when the switch opens due to a pull up resistor on the tinyG board.

    Reference:Schematics for V7 and V8 can be found here

    January 24, 2015 at 1:15 am #7309
    Jim
    Member

    Thanks for the reply. Yes, I am trying to be careful, which is why I switched to the TinyG forum. That said, I am a bit confused by your response (and I am not an electronics engineer so I am not that good at reading and understanding schematics). You said I will wire the switch between 3.3v and Gnd. Don’t I need to wire it between a limit input like xMin, xMax, etc. and the other to Gnd or 3.3v? If I just hook one leg of the switch to Gnd and the other to 3.3v how will TinyG know what limit has been hit?

    Forgive my ignorance, but like I said, I am not an electronics engineer.

    January 24, 2015 at 6:23 am #7310
    cmcgrath5035
    Moderator

    You are correct, my wording is a bit confusing if you are not good at schematics.Sorry about that.

    Each of the switch input ports on tinyG are connected individually to 3.3V thru a “pull up” resistor on the tinyG board.
    If nothing is connected to the port, or an NC switch which is operated (therefore open), the port pin will be high logic level.
    If NC switch is in the normal, Closed position, the port pin will be at low logic level,GND.

    So, NC switch, one lead to GND and on lead to the port pin.

    It is best to use shielded two wire cabling for noise minimization.
    Ground the shield at the tinyG end ONLY, not both ends.

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