FAQ Mach3


 

 

 



Do I need to use Home or Limit Switches?

You can run your entire machine without using a single home or limit switch.

Home switches are added to only one end of an axis, so that you can zero out your coordinate system on that position, and have a repeatable known zero every time you use your machine.

Since you have that switch there, it is usually also assigned as a limit switch (positive or negative depending on your direction of travel), but you don't need to.  This will just keep Mach from commanding your machine from going any farther in that direction.  

At that point, you can chose to install another limit switch switch on the opposite end of your axis to keep Mach from commanding your machine from going any farther in that direction.  Since this switch doesn't require generating a repeatable zero position like your home switch, this one can be much cheaper.

 


 

 



Dedicated inputs and bidirectional pins set as inputs will have essentially the same 4MHz input capabilities. The one main difference to not is that the dedicated inputs have a 4.7K pull up resistor and the bidirectional pins will have a 47.K pull down resistor.  But this is just on the ESS.  If your BOB just passes inputs straight through, then this is what you need to consider.  If your BOB has electronics added to each input pin, then you would have to look and see if they are pull up or pull down style inputs.

If you are applying [b]5V [/b]to one side of a NO or NC switch, you would want that hooked up to a pull [b]DOWN [/b]input.  When the switch is conducting, the switch will source 5V, and the input pin will show as HIGH (since the current limited pull down resistor will not be able to sink all the current sourced by the switch). When the switch is not conducting the input pin's pull down resistor will sink any residual charge and the input pin will go to 0V and read as LOW.

If you are applying [b]GND [/b]to one side of a NO or NC switch, you would want that hooked up to a pull [b]UP [/b]input.  When the switch is not conducting the pull up resistor will source 5V and the input pin will show as HIGH. When the switch is conducting it will sink the (current limited) 5V from the pull up resistor; the input pin will read 0V or LOW.

You should use:
5V with NC to a pull down input, and you would set this to active LOW. - OR-
GND with NC to a pull up input, and you would set this to active HIGH.

The reason for this, is that if a wire breaks or comes lose, then the input signal will activate immediately, and you will know something is wrong.


Homing signals just act as homing signals, never limit signals.  However you can assign the same input pin to both a homing signal and a limit signal.

The same switch can be both a home and either a positive or negative limit switch.

The main reason to not have a home switch also be a limit switch, is if you have a a tool change area past the home switch, and you put a limit switch just past the tool change area.


Here is a follow on that you will probably ask about next...


The bidirectional pins set to output current is designed to drive (sink) +(-) 32 mA. The directional output pins may drive (source) up to +24mA of current (in positive logic or active high mode) or sink up to 24 mA of current (in negative logic or active low mode). As far as the ESS is concerned you can drive equally well with positive or negative logic.

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