Hi
Most scales use a device called a load cell which is like a Z shaped chunk
of metal that gives an output proportional to load.  These use a strain
gauge principal.  Try the South Africa branch of Maplin Electronics.  They
should get you strain gauges or try RS Components.  Remember to use at
least two sensors.  It gives the best readings.

The CPR practice doll I was using during a heartstart course used a large
spring and a slotted opto switch with a very fine scale that went through
it vertically.  This gave amazing accuracy and was cheap and easy.  As below

___________Surface____________
///             -               ///
///             -               ///
///             -               ///
///             -               ///
///             -               ///
///             - _____ ///
///           |-|_____| ///Spring
///                     |       ///
///                     |       ///
///                     |       ///
///                     |       ///
///                     |       ///
///                     |       ///
///                     |Post   ///
_____________________|_________


   _____
|-|_____| Represents slotted opto switch

As pressure is put on spring, a pulse train is output.  The post limits
maximum weight and should come to half total height.


Tim


At 08:46 25/08/97 +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
>
>


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