On Thu, 24 Jun 1999 00:09:00 +0930 Ross Bencina <rossb@AUDIOMULCH.COM>
writes:
>Hi PICsters,
>
>I have a 12 position single pole rotary switch that I'd like to
>interface to
>a 16F84 and I don't have 12 spare IO pins ;) (Ideally I'd like to use
>4 pins
>or less). I've seen examples of using a resistor lader and an RC timer
>circuit (uses too much cpu time for my purposes), presumably there's
>also a
>logic chip (demux?) that will do the job, I'm just wondering if I've
>missed
>any other obvious, minimal, and/or clever solutions to this problem.
>
>Thanks in advance.

        I'd probably use the switch to tap off a 12 resistor voltage
divider, then go into a single analog input pin.  However, since the 84
doesn't HAVE an analog input, you'd end up doing A/D with an RC circuit,
as you suggest, then dismiss based on CPU time.  There ARE 15 bit
encoders, but they tend to be pretty big.  Also, this'd use 4 I/O lines.
A 16 bit shift register could bring in 16 lines using 3 I/O pins (data,
clock, load).  You could hang other shift registers on these same lines
for even more I/O.

Harold



Harold Hallikainen
harold@hallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

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