Well, you're in the ball park but in the dugout!  Just kidding.....

Check this Microchip app note:
  http://www.microchip.com/Download/Appnote/Category/12CXXX/Sensor/3_001.pdf

This is the circuit someone refered me to and one I would like to try.  I
just don't know what L and C to use (or how to calculate the length of an
etched coil).  It was suggested that each mm of trace would be about 1uH (I
think).

I don't necessarily need to use 333khz either.  I do realize that the lower
F the longer "antenna" coil.  But I need to watch how high I go using PIC at
4mhz crystal.

Since this circuit is simple and I only 6-12" useful range,
what do you think I should use as an F - C - L combination???

John Mullan

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Stouchton
Sent: Tuesday, December 05, 2000 1:23 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE] Inductive signalling


Hi folks,

        I'm jumping in mid-post here and might have missed something.  If
one is
attempting to xmit some fixed distance via magnetic field, then inductance
is bad.  It complicates the ability to get the desired current in a given
time.  However, it all depends on how far one needs to transmit.

        For short distances (about 2' or less) a simple trace (or 2 or 3)
around
the outside of a 4"x4" pcb should do the trick.  You can use Biot-Savart law
to calculate the current requirements to develop a particular flux
density... however you do need to know your overall receiver sensitivity to
start.

        If there is a current limitation, then you will need MANY turns and
considerable inductance will be present.  Then you will need to series
resonate the inductance so one is left only trying to drive current through
the resultant resistance.  Beware of Q and other nasty things that change
the rise and fall time and limit communication rates.

        If I'm in the right ballpark and you need more info just email...
I've had
in excess of 10 years experience in this area and might be able to help.

        If I'm on the football field with my goalie pads on, just ignore me.

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of David VanHorn
Sent: Tuesday, December 05, 2000 12:54 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE] Inductive signalling


>The track can be zigzagged to fit it into the required space, but according
>to your earlier post, you need to fit 150mm of track onto your board for
>150uH.


Use the cores luke!

Put holes in the board to accept an RM-4 or RM-6 core.
Now, you use the AL value of the core to determine the inductance. :)
Turns as needed, printed on the board.
--
Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9

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