I can think of two possibilities:

[1] They may be using an optical encoder.  If so, then the LED's on
the encoder will need to be powered somehow.  While the design could
use four pins [use a common terminal for the LED's and for one leg of
the phototransistors] some applications may require switching the LED
on and off [e.g. turning it off while not looking at it]; this is
much easier if both legs of the LED are "exposed".

[2] They may be using a 16-position encoder.  While 16-position
encoders [which have a 4-bit output] are a little more expensive than
4-position ones, they can be more reliable when moved quickly.  On a
4-way encoder, if you move more than one click between samples the
device will be misread; on a 16-way encoder, you can move seven
clicks per sample time without missing counts.





I just took the switch out.

1. it is potentiometer.
2. pin number 2  not used
3. measuring between 1 to 5 has 8.5 k resistance.
4. pin 3 which is middle one works like regular potentiometer.

basically the way I understand it is based on resistance value
probably something like this

using ADC PIC16C73 can be done but what about pin 4?

changing the value with this method I think it is Advanced way of
doing it of course you can use 2 buttons too.

any idea will appreciate.


        thank you

Andre





















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