This is a simple 2020 extrusion mount for an emergency stop button. I wanted something that would immediately cut motor power in case something got stuck for example. While other methods such as a button to cut printer power was an option I didn't like the fact that the fans would also be stopped. This can lead to clogs due to heat creep. My solution was a software one, hooking into Marlin to Kill the printer but keep the fans running.

This can be done by defining a 'KILL_PIN' in the Marlin firmware and your board's pins file.

This is an example of the pin I used on the SKR v1.3 mainboard. I used the X-MAX end-stop pin as it was unused.

If your button is reversed, i.e. is triggering when not pressed, then you can reverse the pin trigger state in the MarlinCore.h file. Change LOW to HIGH:

The button I used can be bought here: https://www.aliexpress.com/item/32800114918.html

I've also included a contacts cover for the button to prevent debris from triggering the KILL state.

Hopefully this is useful to someone. :)