At 09:40 PM 3/15/02 -0500, you wrote:
>Thanks!  This suggestion was about the fastest to implement and it worked
>first try.

Always good to hear.

>  The display is extremely dark with a 0% duty and unreadably
>light at a 100% duty.  It looks great at 48-55%.  It made no difference with
>or without a cap.  Is there any reason this method should pull significantly
>more power than the datasheet's method?  Both are voltage dividers using
>resistors...  The datasheet suggests a 10k-20k pot and the circuit below
>uses about 1.5k total.  With a 10k and 1k instead of 1k & 470, the display
>looks good from 25-35% duty.

With the pot you can crank it all the way down in voltage and the source
impedance drops to zero, yet the pot draws only 250-500uA. With the divider
you're stuck with the 320 ohms output impedance with my suggested method or
with 900 ohms with yours. The problem is that there is significant current
flowing *out* of the  contrast adjust pin, so if your source impedance is
too high, the display can't be made dark enough at low temperatures (even
with a PWM of 0%, you'll still see a lot of voltage at the contrast pin).
With a pot, it just makes the setting a bit more non-linear near the
minimum voltage setting (maximum contrast).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.