This is a (fairly) simple meter to measure magnetic polarity and field strength. It might be useful for motor projects etc but i built it for something else.
I am trying to improve the magneto on my 1921 Ner-a-Car. Part of this is experimenting with pole pieces also magnetising the parts separately and/or in-situ. To know if this is working I needed a way to measure magnetic dield strength.
I already had a LilyGo TTGO T-Display (ESP 32 version) and a bag of suitable Hall sensors, so only needed to buy a battery and print a case.

BOM:
LilyGo TTGO T-Display ESP32 https://www.amazon.co.uk/gp/product/B099MPFJ9M
Honeywell SS49 Hall sensor (eBay, some time ago)
250mAh battery https://www.amazon.co.uk/gp/product/B08215N9R8
5.08mm square DPDT latching swith (eBay 154150955718
2 x M2 CSK screws
Case https://a360.co/38wiQvt