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'Followup: Re: Best way to interface a 12 pos rotar'
1999\07\05@140154 by Ross Bencina

Hi all,

Well it took a while but I've finally finished my first PIC project, my
first self designed electronics project too. It's a combination MIDI knob
box and voltage to MIDI converter.

A couple of weeks ago I posed the question "What are some clever ways of
interfacing a 12 pos rotary switch to a PIC", there were a number of
different responses and I'd like to thank everyone who responded for your
help - I learn't a lot just reading the different ways it could be done. I
ended up using a solution based on a 4017 (thanks Morgan Olsson for that

I connected the 11 outputs (including carry) of a standard CMOS 4017 decade
counter to 11 of the 12 switch terminals, the 12th switch terminal was tied
to ground. I tied clock on the 4017 to +5ve and connected reset and
ClockEnable to separate pic pins (I had a few spare). The common switch
terminal was connected to another PIC pin. The switch was less than 6inches
from the main PCB so I took the chance and put the 4017 on the PCB and used
a ribbon cable to connect them - I might try gluing the chip to the back of
the switch next time.

The PIC steps the 4017 though each state (1 to 10) checking the common
switch output as it goes. If the switch is switched to the carry output the
switch output will be high for the first two 4017 clocks, otherwise the
common switch output is high at only one clock phase, or at none for the
grounded switch position. I used a lookup table to remap the returned
numbers to the correct program states.

Somehow I managed to blow up RB1 on a 16F84 while working on this, it just
stopped outputing data - I guess I'll save that chip for something that
dosn't need RB0...

Thanks for your help, PICList forever!


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