Check out these cnc machine images:
IMG_2217
Image by smellsofbikes
3D probe assembled. The pointy bit at the left is the touch probe itself. The blue wires are the sense, the red is the power. Power goes to the probe tip, and the blue wires measure continuity between the tip and the three screws.
IMG_2215
Image by smellsofbikes
3D probe disassembled. The pointy tip at right goes into an aluminum conic section that sits on the three levelling screws, providing a circuit from the tip to each of the three blue wires. The spring fits in the cup and pushes the probe tip downwards.
IMG_2216
Image by smellsofbikes
3D probe assembled. This is the logic board: a 3-AND chip with five LED’s (power, each of the three switches, and the logic chip output.)