Hood's advice to use MachMad is good. It only costs $10. Then you can have all sorts of remote triggers.
However if you want to do it this way, here is a copy of an old post of mine regarding having a manual button for a macro.
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A brain can not trigger a macro on it's own. So the macropump does that.
However brains are a no brainer to implement safety timers and lockouts. (pun intended)
The auto tool zero macro needs to be placed in the macro folder with the name of your profile. Eg. Mach3Mill. Call it M615.m1s
The macropump calls the relevant macro when a user LED goes active.
It basically is one which Poppabear wrote for me a while ago. Much the same as posted above.
The brain sets the LED when the switch is pushed and held for 1.5 seconds but only if there is no motion, the spindle is not running and reset is not active.
Being an external momentary switch I think the 1.5 second delay is a good safety measure.
This means you must push and hold the switch for 1.5 seconds before anything will happen.
You do not want unintentional activation of the macro.
So the addition of the brain is just to allow for easy implementation of the safety lockouts.
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Have the momentary switch activate OEMTRIGGER#5
Remove any initial delay in the auto tool zero script. The brain now handles that.
Try it if you wish,
Greg