Which PIC are you using?  Most that I've worked with have a 10-bit A/D, s=
o=20
you'd actually get a range of 0-1023, and instead of 2.125, your steps wo=
uld=20
be 8.5.

I actually prefer to do the math and reduce the number of components, but=
 if=20
you need more resolution from the A/D, then how about using a 3-resistor=20
voltage divider with the 2 center points going to VREF+ and VREF- of the =
A/D=20
converter.  Something like this ...

      +V
       ^
       |
      [R1]
       |
       o----> To Vref+
       |
      [R2]
       |
       o----> To Vref-
       |
      [R3]
       |
       v
      GND

In this case, the A/D will read "0" when the sampled voltage is equal to=20
V*(R1+R2)/R3 and 255 (or 1023 if using a 10-bit A/D) when the sampled vol=
tage=20
is equal to V*R1/(R2+R3).  Remember that there is a minimum difference=20
allowed between Vref+ and Vref- (~2V for some of the 16F-series chips IIR=
C)=20
-- see the datasheet for the official spec.

Cheers,
-Neil.


On Saturday 03 January 2004 10:25 pm, reinaldo@IHUG.CO.NZ scribbled:
> sorry i was very vague
> the headlight motor is a simple DC motor, and i'm going to
> fit a resitor pot to the headlight to measure the angle of
> the headlight, say this pot gives me 80 when the light is
> down and 200 when fully open, the pot in the dash will give
> 0 to 255 ofcourse. so i'll need 0 to equal 80, 200 to equal
> 255, AND every 2.125 steps of the dash pot correspond to 1
> step of the headlight pot. i can't measure .125 from a pot.
> but, i'll measure the dash pot(say 60) divided 2.125 =3D
> 28.23.. so that's 28 steps for the headlight pot + the
> bottom position(80) =3D 108, so now i work out wich way to
> turn the motor untill i reach 108. that way i hope to use
> the full range of the dash pot.
> now you can see i need division routines, i need to store
> top and bottom levels while the power is off, and i also
> need to constantly calculate what position the dash pot
> works out to be for the headlight pot. i don't dare remove
> the current motor and replace it for a stepper, also
> remember everything needs to be done for both headlights :(
> can you think of a simpler method?
> thanks for your advice

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