Schematics Build Your Own Gauss Meter | Electronic Circuits

Schematics Build Your Own Gauss Meter

Have you ever wanted to find out how strong a magnet really was, or how the strength of the magnetic field varied as you changed the distance from the magnet or the temperature of the magnet, or how well a shield placed in front of the magnet worked? Voltmeters are fairly inexpensive and easy to find, but where do you purchase a Gaussmeter (also known as a magnetometer). I built a hand-held Gaussmeter for measuring the polarity and strength of a magnetic field. It uses a linear Hall effect device and some op-amps and resistors and things from Radio Shack.

Here's a schematic of the Gauss meter circuit (using the 3503 Hall-Effect Device):

With no magnet near the Hall device, measure and note the output voltage reading. Call this V0. It should be about 2.50Vdc.

Now, with a magnet near the Hall device, you will see the output voltage change. If it is a South pole, the voltage will increase. If it is a North pole, the voltage will decrease. Call this voltage reading V1. We will say that the sensitivity of the Hall device is 2.50mV/G as found on their data-sheet. Call this k. Therefore, the Magnetic Flux Density you are measuring from that magnet can be calculated as:
B = 1000*(V0-V1)/k, in Gauss.
Please note that with a calibrated Hall device, you would be given actual data measurements for the V0 value and for the k value.

For example, suppose you measured 2.48Vdc for V0 and 1.32Vdc for V1.
Then B = 1000*(2.48-1.32)/2.50 = 464Gauss, North pole (because it is positive).

For another example, suppose you now measured 4.56Vdc for V1 with the same Hall device.
Then B = 1000*(2.48-4.56)/2.50 = -832Gauss, South pole (because it is negative).

See how easy that is? You can make your own plot using Excel so you don't have to calculate all the time. If you're taking measurements, just write down the output voltage and do the calculations later.
You can simply use it to tell you if you have a North if the output voltage decreased from V0, or a South pole if the voltage increases from V0.

Here are some photos of this simple, inexpensive Gauss meter.

Assembly was easy and exciting, and here is what I've found so far (NOTE: You may know all of this already):
  1. Pickup covers do affect the magnetic field that the strings vibrate in. The most pronounced drop in gauss is over the slug polepieces. The adjustable polepieces have significantly more power than covered ones.
  2. Strat magnets can have a significant difference in gauss in the same pickup.
  3. All magnets are not the same, and PAF pickups have a significant difference in gauss from pickup to pickup.
  4. The Dimarzio PAFs have almost exactly the same magnetic characteristics of a Gibson PAF.
Download Gaussmeter Circuit Documentation

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