Hi All. Sorry for the long subject line. I am working on two loosely
related projects, and I am looking for some part reccomendations for
each, so I though I'd combine them into one email.

First off, I am looking to interface a few pushbutton switches to a PIC
over a length of cable. I figured that Ethernet cables are plentiful and
cheap nowadays, so I would use one of them. I'd like to use more
switches then I could if I was just using one wire per switch. I tried
something sort of similar a few years ago with a BCD to Binary discrete
logic chip, and it didn't work as well as I'd hoped. Now, I might have
been using it wrong, but to prevent that type of problem from happening
again, I figured I'd ask for help. For argument's sake, lets say I want
to use up to 30 feet of cable. The output of the encoder chip will drive
the cable, which will drive the inputs to a PIC. I  don't really see the
need in adding a dedicated decoder to the circuit. BCD would be ideal,
as I could squeeze 16 pushbuttons in 4 lines. Any suggestions?

My second question is about ADC. I need 24 channels of ADC in another
circuit, and I am unsure of the best way to go. I just need 8 bit
resolution, so that isn't really a stumbling block. My two thoughts are
to either use an external ADC, or multiple ones, or to use an analog
switch to multiplex the PIC16f877's internal 8 channel ADC. The only
problem here is that I am measuring a 50K pot, and the input inpeadence
of the f877's convertors is 10K right? I don't really want to have 8
impeadance matching circuits, and I wouldn't even know where to start
designing one (well, opamp, I know that much). If I was to go the switch
route, I was looking at Maxim MAX336 (16:1 switch), or more likely, the
MAX337 (2x 8:1 switch). Any thoughts on these? My other idea, the
external ADC also has some merit. I've never used an external ADC, so it
would be a learning experience. I figure I'd want one that has an
internal reference, and for simplicity's sake, a parallel interface. I
have the spare pins, and it will make my coding a lot easier. I still
have to trigger a conversion right? The ADC doesn't just sit in a loop
converting and then when you ask it, it dumps off the current value? I
suppose that would be too easy. So for the ADC option, I was looking at
the MAX1290 (8ch Parallel) or the MAX197 (8ch Parallel). Any thoughts on
these devices? Any suggestions on which way to go.

Sorry for the long email. I'd appreciate any advice on either or both
questions. Thanks!

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
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