Don Foreman wrote:

On Fri, 16 Jan 2009 18:29:57 -0500, Wes wrote:

Don Foreman wrote:

Many industrial sensors integrate this function with a circuit that
switches at some level of field intensity, providing a binary or
"on-off" signal. I'm using a linear hall sensor that provides a
voltage proportional to field strength, about 4.25 millivolts per
gauss. It's the HAL400C from Micronas. Current product would be the
HAL401:

http://www.micronas.com/automotive_a...ion/index.html

Why that one? Because I had 4 of them in my junkbox. Allegro also
makes Hall sensors, and Honeywell used to, probably still does. I
like the differential output on the Micronas for rejection of noise. 4
millivolts isn't much signal when 60 Hz is in the passband. You
probably know what happens when the ground comes loose on a microphone
or magnetic phono jack: HUMMMM! I want this sensor to sense magnetic
field but ignore E field. I'll measure that separately.



Sheesh, you have a nice junkbox. I tried newark and digikey and they
didn't carry it.

I got it from DigiKey some time ago. It's not a current part, I've
had it awhile. Parts now available from Allegro, Melexis, Honeywell
and others may well be better.

You can also often obtain them from the brushless motors of old floppy
drives, etc. They often use three hall effect sensors to determine the
angle of the magnetic rotor, in order to commutate the current to the
windings of the motor. You'd have to guess at the specifications, but if
in doubt about how to use it, you could measure the voltages with a scope
whilst it is still working in the floppy drive.

Chris