Re: Changing photo resistor resistance range.


"Endoscope" <looking@xxxxxxxxxx> wrote in message
news:SNeae.1360$p06.1085@xxxxxxxxxxxxxxxxxxxxxxx
>
> "John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
> news:0ifi61d12qfbpm9vslp6rqr175lh4cuuh2@xxxxxxxxxx
> > On Fri, 22 Apr 2005 10:27:02 -0700, "Larry Brasfield"
> > <donotspam_larry_brasfield@xxxxxxxxxxx> wrote:
> >
> > >"Chris W" <1qazse4@xxxxxxx> wrote in message
> news:Siaae.375$XA2.65@xxxxxxxxxxxxx
> > >>I have a photo resistor that varies from about 400 ohms to about 15
> million ohms in the desired light conditions. However I need
> > >>something that varies in resistance from 1k to 5k. Is there a way to
do
> this with a transistor? The circuit will always be
> > >>supplied with a 100mV supply which I suspect will effect the design of
> what I am trying to do.
> > >
> > >
> > >What's wrong with the following?
> > >
> > > o
> > > |
> > > .-----o-----.
> > > | |
> > > .-.
> > > | |
> > > | 6.2K | |
> > > .-. '-'400 to >1M
> > > | | |
> > > | | |
> > > '-' .-.
> > > | | |
> > > | | | 620
> > > | '-'
> > > | |
> > > '-----o-----'
> > > |
> > > o
> >
> >
> >
> > ---
> >
> > R1 = 6.2k
> > R2 = 400 -> 15M
> > R3 = 620
> >
> >
> >
> > R1 (R2 + R3)
> > Rt = --------------
> > R1 + R2 + R3
> >
> >
> >
> > 6200 (400 + 620)
> > Rt1 = ------------------ = 875.9 ohms
> > 6200 + 400 + 620
> >
> >
> >
> > 6200 (15e6 + 620)
> > Rt2 = ------------------- = 6197.4 ohms
> > 6200 + 15e6 + 620
> >
> >
> > 875.9 ohms to 6197.4 ohms isn't 1k to 5k.
> >
> > --
> > John Fields
> > Professional Circuit Designer
>
> To which Barry should reply.
>
> Whoops! Sorry, Brane Fart...... Try 5K1 and 820R.....
>
> Don't hold your breath though.
>
> DNA
>
>

Oh ***, Barry might be Trolling/Teaching. His question was......

'What's wrong with the following?'

Oh ***..... I've just given him the opportunity to write 300 lines of
explanatory dribble.

Argggggghhhhhhhhh!!!!!!!!!!!!

Kill Me NOW.

DNA


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