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'Analog/Digital Conversion'
1995\12\15@135735 by

I am using a pic16c71.  My goal is to be able to measure the voltage
created by a pot.  How can I get the pot to show 0 to 5 volts as a
voltage dropper?

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Ben Kwok-Yiu Li wrote:
>
> I am using a pic16c71.  My goal is to be able to measure the voltage
> created by a pot.  How can I get the pot to show 0 to 5 volts as a
> voltage dropper?

Connect 1 end to ground, the other end to 5V, and the slider (center pin
on nearly all pots) to one of the A/D pins on the PIC.  Also, I would
reccommend putting a 1K resistor between the slider and the PIC.  This
will prevent the PIC from being damaged if the pin inadvertently gets set
as a digital output.  A small capacitor (470 pF is a good value to start
with) will help keep the A/D from picking up noise.  This is especially
important if the pot will be more than a couple of inches from the PIC,
or if there will be a lot of electrical noise.  The reccommended circuit
is below:

+5V
-----
|
---------                      |
|                     \
|                     /
16C71   |---/\/\/\----------->\
|   |                 /
|   |                 \
---------  -----               |
-----               |
|                 |
|                 |
-----             -----
---               ---
-                 -

The resistor and capacitor should be as close to the PIC as practical.
The value of the capacitor can be increased if the operating environment
is extremely noisy.  The value of the pot should fall in the range from
1K to 100K.  Lower values give better noise immunity but will dissipate
more power.

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