Extremely simple but accurate bed leveling probe.

thingiverse

As is, fits Creality Sprite Pro extruder assembly. Requires a 17mm microswitch, a few small magnets,, a couple m2 bolts and a couple m3 bolts. Also a couple v-slot rail nuts for attaching it to your rails. Depending on the printer you may need to re-shape the deploy pedestal. Small magnets (with or without a metal plate) are glued to the switch holder so that they can hold up the switch's lever. Depending on the switch lever's material, you may need to solder something magnetic to it (I used a couple staples). Bigger magnets (with or without an iron plate) are attached to the pedestal piece (easiest to superglue a piece of metal to it first then stick the magnets on for adjustment, then superglue magnets in place). Bigger magnets should be able to pull the lever away from the smaller magnets; that is most easily accomplished by placing them in opposite polarity. If you have trouble getting probe deployment to work, you can put a piece of thin tape over the smaller magnets to add a slight gap. The probe is auto-deployed by touching down on the pedestal, and stowed by ramming it into the build plate. It also get stowed as part of homing, in the event that printer is powered down with the probe still deployed. Wire the probe to normally-closed contacts on the switch, use INPUT_PULLUP on it. Microswitch break contact before they make contact, so detecting break is slightly more accurate (less speed dependent), allowing faster probing. I connected it between ground and signal line for bltouch, using the connector already present on the sprite extruder. Accuracy: 0.01mm or better. Test results with deploy/stow cycle for each probe: Mean: 0.519500 Min: 0.517 Max: 0.527 Range: 0.010 Standard Deviation: 0.003500