At 08:46 AM 8/25/97 +0200, you wrote:
>Hi to all.
>
>I was wondering if anyone out there has attempted to make an
>electronic scale using PIC's. I have a few ideas for the PIC side
>of things but 'What to use for a SENSOR??' I was thinking of
>strain guages but over here in sunny South Africa, these are either
>hard to come by or very costly. I'm considering a LVDT (Linear
>Variable Differential Transformer) option but I wan't to keep
>mechanics to a minimum. I was wondering if any of you out there have
>some idea's that you would like to share on the topic.
>
>Thanks.
>
>P.S. Thanks to Mal Goris, Andrew Errington and Don McKenzie for
>their help, my programmer is now up and running!
>
>Jacques Vrey
>Iscor Profile Products Newcastle
>Tel:27-(0)3431-48759
>jvrey@it.new.iscorltd.co.za
>
I was at a customer's place one day and he explained to me how his Metz__r
scale worked.  The principle is pretty slick.  A balance is attached to the
plate.  A sensor ( i forget, magnetic or optical) sensed when the balance
was centered.  The other end of the balance has a low tech solenoid
attached.  The circuit adjusts the current through the solenoid until the
balance balances, and voila, the current being sent to the solenoid is
proportional to the weight.  I am sure there are issues, such as
temperature compsation, but Metzler (oops) solved it, that scale was super
accurate and not cheap.  But on that principle, you could develop a
reasonably cheap version.  I was tipped off to ask him about the darned
thing when I noticed that the platter did not apear to deflect at all.
Word of warning, I would check and see if they have a patent on the
principle.  It is too neat not to.

Chris Eddy
Pittsburgh, PA