I have been trying to design the ultimate Electronic Edge Finder (EEF) for over 4 years. It had to be low cost, work over a wide range of spindle bearing electrical resistances, and be 100% reliable. Well, maybe this time I have it.
This EEF is built on a Harbor Freight Multimeter which commonly goes for $6 if it is not being given away for free. The added circuit should cost under $5. It can detect changes in resistance as low as 0.1 milliohms but typically only needs to detect changes of tens of milliohms. The user is warned if the spindle resistance is too low to detect touchdown. A twist of the spindle brings it back into range. Low battery indicators and a bad connection indicator are also included.
If you are interested, please see
Your comments are welcome. All of us are smarter than any one of us.