A friend has some stationery engines - a few with weak magnets in the magneto, we are planning a remagnetiser and to try to make the project more technical I built this gauss meter so we can check our progress without having to resort to assembling motors etc to test for spark - I had all of the bits in my 'spares' bin except for the hall effect device, the info came from this web site.

https://rimstar.org/science_electron...display_ba.htm

Not having a digital panel meter that can be used with a single supply( ie effectively measure it's own supply voltage) I used a salveged 50uA moving coil meter that still worked fine but had seen better days. At power on the meter indicates 1/2 scale and deflects either to the left or right depending on the magnet polarity that is bought close to the hall device - the stronger the magnet field the greater the deflection, the LED's red or green are a quick indicator of the either N or S. I'll eventually get some nylon tube to protect the wires and hall device socket, being in a socket I can plug in more sensitive hall devices - the current device outputs approx 1.5mV/G, a strong neodymium magnet gives a deflection of around 2V either plus or minus depending on the magnet polarity. The hall device is not calibrated - the 1.5mV/G is only the typical output voltage for that device so all meter reading are only relative to each other - I believe calibrated hall devices are available so a calibrated meter could be made.

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