Roxy,

I have 2 Lulzbot TAZ 4's and I'm trying to implement auto bed leveling using Marlin the way Lulzbot does with their newly released TAZ 6's as shown here starting at 33 seconds:

https://www.youtube.com/watch?v=JKkerkp3l5w

My TAZ 4's are set up similar to the TAZ 6 in the video except I don't have the button switch which is the first thing you see being tapped in the video. I'm currently using Marlin's G29 to tap the four corner washers and create a print plane and I'm getting great prints, but first I have to wipe the nozzle w/ a Scotchbrite pad to make sure it's clean for electrical contact with the washers.

I want to implement tapping the button switch, but Lulzbot created a lot of new wiring so the switch and the corner washers are on separate circuits. The button is tapped by the hot end to approximate the bed height so if the nozzle is not clean it will not continue to drill down into the washers; instead it will back off and try wiping again.

I would like to keep it simple and keep the button switch and the corner washers on the same circuit. Is it possible to set up Marlin to start w/ a G28 to tap the button switch and then if a G29 on the corner washers causes the nozzle to go x mm below the G28 tap then the hot end will back off and try the wipe again? Thank you.