I thought I would do a side project. I was looking at gauss meters and they are $90 for a cheap one and go up from there. Admittedly they are calibrated and mine isn't, but it works well enough. I basicly wanted to be able to check north vs south and to check magnet strength. I have a stack of magnets that are supposedly N52. At least that's what I ordered, but without a real way to test them, I've never known. Now I can try them out and see if they really are N52 or not.
I used an S49E linear hall, a small 1 cell charge controller that includes a BUCK to 5 volts and a 150mah cell from a nano quad of mine. I super glued the hall to the end of a 6" long dowel and ran the 3 wires down the dowel. The +V and gnd wires go to the BUCK output to power the hall. The signal line and gnd come out to a 2 pin connector for connecting to a volt meter. These are the main components that power the gauss probe. I think I have $5 all told into this. The lipo cell cost about a dollar. I bought 5 of the buck/charge controllers for $3 and another dollar for the hall.
This is the completed gauss meter. It's 7" long. I could have made it a lot shorter, but the length makes it into a probe that can be stuck down inside places. I added a micro USB connector to the charge connections on the controller board so I can charge via any USB port. I covered the hall wires down the dowel in heat shrink, wrapped the battery and charge controller in kapton and strategically used hot glue to secure the dowel and USB port to the board and battery. A liberal use of heat shrink and a couple of small zip ties holds it all together. The linear hall with no magnetic field present outputs 2.583 volts. With the north face of an N52 magnet touching the hall it goes down to .78 volts. With the south face of the N52 magnet touching the hall it goes up to 4.3 volts. There's a simple equation to do to take the output voltage and convert it to gauss.
Gauss = 1000*(V0-V1)/k
V0 is the qiescent voltage or 2.583 volts.
V1 is the measured voltage
k is the mV per gauss or 1.4 mV/G for the S49E hall.
The north side measures .788 volts and the south side 4.29 volts. That calculates to 1280 gauss for the north side and -1221 guass for the south side.
I also have a stack 20 neo's I bought on ebay. They were advertised as N50, but I got them and just doing strength tests with them, I knew it was BS. Anyway north measures .857 volts and south 4.28 volts. Definitely weaker than the N52 magnets. I checked a few motors to see how strong the magnets are and none of them measure as high or as low as the N52's. Looks like it's working.