Hi Jinx:

What I'm trying to do has not been done before.
Hall effect devices are typically used with strong magnetic fields, i.e. ne=
ar magnets.
The Allegro app notes are all aimed at that application.

Yes, the circuit at magnet.htm is using a couple of pots to generate curren=
t to buck out the Hall offset.  This circuit uses a split (+ and -) power s=
upply but they are only using a positive output, don't know why.  But again=
 here the magnetic field driving the Hall effect device is from a nearby ma=
gnet, not the earth's magnetic field.

I think I have figured out how to do the subject circuit.  Step one is to t=
ake the PWM output through a simple voltage divider changing the output to =
zero to 0.2 volts (i.e. divide by 25) and place a very large cap that's goo=
d at the PWM output frequency across the bottom resistor, now the output is=
 a DC voltage with some ripple that can be added to 2.4 volts from another =
voltage divider.

Have Fun & Happy Holidays,

Brooke Clarke, N6GCE
-- =

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com



Date: Tue, 27 Dec 2005 11:30:25 +1300
From: Jinx <joecolquitt@clear.net.nz>
Subject: Re: =

To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Message-ID: <005e01c60a6b$f924ba30$0100a8c0@ivp2000>
Content-Type: text/plain; charset=3Diso-8859-1


>> It is a Hall sensor.  The quiescent voltage spec with no magnetic field =

>> is about 2.5 =B1 0.1 V
>  =

>

Have you tried specific interest groups ?

http://www.magnetometer.org/

http://www.pacificsites.com/~brooke/Sensors.shtml (??!!)

http://www.uksmg.org/magnet.htm

Is the resistor-based adjustment in that circuit something like
what you have now ?

634SS2 datasheet (169kB)

http://www.farnell.com/datasheets/34553.pdf

Did you see the thread "[EE] Use 405x instead was 4066 help" from
the third week of 12/05 ? In it was described the technique of using
PWM to make a variable resistor with a 4066, Perhaps you could
forget about making a variable V and make a variable R instead

-- =

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