Hall effect sensors: read the !@#$%^& manual

Other Hardware Sensors
1

Kicking myself....

I have a ratiometric hall effect sensor, works as expected. That is to say, apply 5V and Gnd, measure 2.5 at output. That then drops gradually to 0V or rises gradually to 5V in the presence of a magnetic field, depending which way the magnet faces as it approaches.

Then I bought a unipolar switch one, expected Vout to switch high and low as the magnet approached or receded. I knew as a unipolar it would work only on one face of the magnet but it worked with neither.

Lots of head scratching.... same test rig as with the ratiometric one and 'scope settings the same, why it not working?

Resorted to reading past page 2 of the datasheet.... 820R pullup on the output to Vin and voila!

Lesson learnt (again).... RTFM.

2

That wasn't just a self-kicking rant, btw, else I'd have put it in Bar Sport. It might actually help other folk using these things.

Datasheets:

Ratiometric

Switch (see circuit (pic B) on p7)