Which pole, which way
One pole raises the output and the other lowers it, because the field passes through the chip one way or the other. By the data sheet's drawing for this package, a north pole over the front raises it; the same pole behind the board lowers it. The maker's drawings disagree between packages, so check yours once with a compass.
Through the chip, one way or the other
A magnet's field comes out of its north pole and goes back into its south pole. Held over the front of the board, a north pole sends the field through the chip from front to back, and a south pole from back to front. The chip's output follows that direction: one way raises it above half the supply, the other lowers it below.
Pick the pole and the side. Two changes swap the direction, and they undo each other: turn the magnet over, or move it behind the board, and the output goes the other way; do both and it goes the same way as before. The board is only 1.6 mm thick, and the field passes through it as if it were not there.
Which pole raises it
Slkor's data sheet shows its SOT-23 chip, the one on this board, with a
north pole over the top face raising the output. The same sheet shows its
TO-92 version with a north pole on the marked face lowering it. Both
cannot be the same rule for the same chip, and this board has not been
checked against a labelled magnet. This book follows the SOT-23 drawing,
and the sketches keep it in one line, NORTH_RAISES, that you can flip.
Check your own once. The end of a compass needle that points north is a north pole, so it swings toward a magnet's south pole. Find your magnet's south face that way, hold it over the front of the board, and see which way the reading moves.
The silkscreen pairs N with an up arrow and S with a down arrow. If the arrows mean the output, that agrees with the sheet's SOT-23 drawing. It is a label, not a measurement.
When it does not work
First check the magnet is on the front of the board: behind it, the field goes through the chip the other way and every name swaps. If it is on the front and still swapped, set NORTH_RAISES to false in the sketch. The maker's drawings disagree about this for the two packages the chip comes in.
With a compass. The end of the needle that points north is itself a north pole, so it swings toward a magnet's south pole. Bring the compass near one face: if the needle's north end points at it, that face is a south pole.
The chip senses only the part of the field that passes through its face, front to back. A bar magnet held edge-on sends its field across the chip rather than through it. Point a flat pole face at the chip.
Why the supply moves both, and which pin VCC goes to.
VCC sets the zero and the scale →Edit this page — content/books/linear-hall-sensor/which-pole-which-way.mdx
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