Hall sensors can of course be purchased but making them yourself is far more interesting (and satisfying)! According to the theory the crucial thing is to use a touch layer that's as thin as possible; the length and width are unimportant. An 'obvious' starting point for our trials would be copper, which in the form of printed circuit board material is easy to find and handle. Copperclad board may be obvious but not ideal, because it has a very weak Hall constant. Nevertheless, we should be able to use it to demonstrate the Hall effect by using very powerful magnets in our sensor. To achieve detection, we need the highest possible level of amplification. In the circuit shown here the voltage amplification is set by the relationship of the two feedback resistors of the first op-amp, With the values given (2.2 MΩ and 330 Ω) produce a gain of 6,667. This also creates a convenient bridge connection for taking measurements. The trimmer potentiometer allows fine adjustment. With zero setting that's accurate to within millivolts we could use this test point to measure Hall voltages of well below a microvolt. Finally, in this way we could also measure the flux density of a magnet.
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