I'll add two more:

1) Twiddle pots cost money and take up space.

2) Twiddle pots need adjusting and then they fail.

Best to avoid them if at all possible.

--Tom Rogers

-----Original Message-----
From: Andrew Warren <fastfwd@IX.NETCOM.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Wednesday, December 10, 1997 4:28 PM
Subject: Re: Adjusting Contract w/PWM ?


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