Adding a z probe

I built my X-Carve on a budget, so left out the Z-Probe.
I would like to retrofit one.
Could someone give me advice on how to proceed?
Martin Gutzmer

I have the complete x- carve machine 1000mm with a dewalt 611.

I Bought one from “Ghina” - that is actually what it said on the pkg!!
It has an - in theory - a block that is “EXACTLY 1.000 inches.”
plus - I had to laugh - “A nut to adjust it”
Two wires - one for a clip to the bit, and the other to the metal block - enclosed in a plastic base!

old style arduino with g shield

A5 on the Arduino is the probe pin. Connect that to your probe block, connect your endmill to ground.