Can you parallel a small value resistor?
David

PicDude wrote:

> Need some assistance with using a photocell to control the
> brightness of an LCD backlight.
>
> I don't know the current drawn by the backlight, only that
> the datasheet says to use a 5.1-ohm resistor from 5V.  I've
> determined that the proper brightness I need is 10 ohms at
> night, and 5 ohms during the daytime.  The actual curve or
> transition from the high to low value is not critical, but
> I want to use a photocell (rather than a phototransistor,
> etc) so the transition is gradual as it gets darker.
>
> The resistance of Cadmium Sulfide photocells goes down with
> increasing light, which is the correct trend.  However, the
> resistances I can find are all in the K-ohm range.  So now
> I need to figure out how to (simply) translate this into the
> correct resistances.
>
> I can think of many ways to do this "digitally" using PICs,
> PWM, comparators or switching-transistors, etc, but can't
> seem to figure out what to do for a simple linear circuit.
>
> Any ideas?
>
> Thanks,
> -Neil.
>
> ---
> [This E-mail scanned for viruses]
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
David Harris
  OmniPort Home Page:  http://www3.telus.net/OmniPort1/
    Discussion egroup: http://groups.yahoo.com/group/OmniPort
    Swiki:  http://omniport.swiki.net/1

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads