----- Original Message -----=20
From: "Mark Bellamy" <mbellamy@gmail.com>
To: "PICLIST" <piclist@mit.edu>
Sent: Saturday, March 05, 2005 4:34 PM
Subject: [PIC] 10 ohm pot to control contrast on a 16 char x 2 line LCD?


> In the book "Programming and Customizing PICmicro=AE Microcontrollers
> (2nd edition)", it shows a circuit for connecting a PIC to a 44780 LCD
> (Figure 2-25 on page 278 if you are interested).
>
> What I don't understand is it shows a 10 Ohm pot connected in a simple
> voltage divider fasion (One pin to VCC (5v), one pin ground, and the
> wiper pin to the contrast control pin on the LCD).  My understanding
> is that .5A will be wasted though the pot (I =3D E / R =3D 5 / 10 =3D .=
5).
> It will also be dissipating 2.5 Watts. My spec sheet shows that the
> max current drain of the LCD is 4 mA.
>
> So my question is doesn't 10 Ohm seem way low?  Maybe 10k or 100k?
>
> I checked the errata for the book at http://www.myke.com/pic-book.htm
> and it doesn't list this issue.

Must be an error.  10K should be fine, but 100K may work ok too.  Just
grounding the pin should work as well, but it might be a tiny bit off on
the viewing angle, it depends upon the specific LCD.

--=20
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