Hall effect sensors (by )

At the Bristol Hackspace this evening, I powered up a Hall sensor.

The Allegro A1321 takes a 5v supply and outputs 2.5v - plus or minus 5mV per gauss of magnetic field in the sensor.

It turned out that small magnets don't produce many gauss, so I added a 741 op-amp with a gain of about 100 to get more useful output voltage deflection!

Here's the experimental setup:

Allegro A1321 5mV/G hall sensor and a 741 op-amp

WIth no nearby magnets, we read about 3v:

Quiescent: 3v

But with a very nearby magnet, we get a large deflection, which drops as we get the magnet many cm away, but is still significant:

Magnet brought very close Magnet a few cm away Magnet many cm away, still showing a reading

Clearly we still get significant readings a good distance away, and the nonlinearity isn't too bad; it doesn't max out with the magnet very close but still varies many cm away.

For my next trick I'll make a few of this circuit on some veroboard and hook the outputs up to an AVR with several ADCs that I have lying around, and try comparing the results to measure position (and maybe orientation?) of a magnetic probe...

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