Andy, I understand your points but if a user has to adjust the
display, I should think a pot would be more intuitive. I still use
a Radio Shack graphics calculator for quick calculations and it has
a contrast menu where you use the left and right arrow keys for
adjustment. It get's in my way... You can scale the pot value with
a resistor or two to ensure that there is a minimum display.
Temperature compensation can easily be added for any method of
adjustment. For water-tight applications you are dealing with
hermetically sealed components be they switches/keys or pots.
If you already have the switches/keys and available program
memory then I can see a software approach. It just seems like a
lot of overhead for such a simple task.

   The reason I jumped in on this thread is that it seems to be a
classic case of `over PICifying' which I have been guilty of ;-)
I tend to step back from code solutions and take a hard look at
just what the heck I'm trying to accomplish here.

   What this really boils down to is human factors. One customer
may prefer peas and another carrots ;-)

   - Tom

At 01:25 PM 12/10/97 -0800, you wrote:
>Tom Handley <PICLIST@MITVMA.MIT.EDU> wrote:
>
>> LCD contrast is very subjective based on ambient light, viewing
>> angle, and user-preference. If you are going to provide adjustable
>> contrast why not just use a pot?
>
>Tom:
>
>I can think of a couple of reasons...
>
>1.  Although it's often used to adjust for viewing angle, the MAIN
>    reason for the contrast adjustment is to compensate for
>    temperature... If the contrast is controlled by software, you
>    can do things like, for example, display "Press a key when the
>    display is most readable" and cycle through the contrast range.
>    Without software control of the contrast, a new user faced with
>    a blank (or black) display might not think to turn the contrast
>    knob.
>
>2.  If the product needs to be water-tight, it's difficult to include
>    an externally-adjustable pot.
>
>-Andy
>
>=== Andrew Warren - fastfwd@ix.netcom.com
>=== Fast Forward Engineering - Vista, California
>=== http://www.geocities.com/SiliconValley/2499
>
>