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[DPRG] OT: Electronics questions (Long)

Subject: [DPRG] OT: Electronics questions (Long)
From: Chuck McManis chuck.mcmanis at gmail.com
Date: Mon Feb 28 16:06:56 CST 2011

This one is useful to roboticists as well so not OT :-)


On Fri, Feb 25, 2011 at 3:03 PM, David M <oicurmt at charter.net> wrote:

> For a personal project, I have a hard-to-reach device occasionally
> needing up to 8 buttons/switches manipulated (none concurrently).
> I would like to do this via a tethered control, or wand-like device
> (kinda like a teaching pendant I guess). Normally, I'd just open it up
> and tap the existing traces out to a header, but lack of space is a
> factor, so I was wondering if this would be a good application for
> an I2C interface. If so, how small could I get a controllor board for 8
> or so switches, and what kind of cost am I looking at? Would it require
> one at each end? The 2 or three-wire I2C comm. standard is what
> attracts me to using it. I am wanting to avoid coding anything.
> (Unless it's simple; I'm a hardware guy, not software. And yes,
> the device needs to stay where it is, even if hard to reach)
>

i2c sucks. Point blank, it just does. If you want to go serial, and this
seems like you do, then use SPI (serial peripheral interface) which is also
a standard but 4 wires instead of 2 and much more reliable.

That being said, your remote device has 8 buttons/switches, so they are
switching something. Are you trying to interpose on those switches (which is
to say your device will replace them) or are you driving a remote actuator
(some sort of mechanical actuator) or something else entirely?

I point out that CAT5 cable (network cable) has 8 conductors (4 pairs). You
could mechanically wire up two sets of four SPST switches/buttons remotely
using pieces of CAT5 cabling to carry the signals to the remote unit through
the remote switch, and then back again. This tecnique was used in the
Petster robots for their "leash" where the teaching pendant just connected
to ground one of 7 inputs (the 8 lines were hooked up to ground and the 7
I/Os) as I recall.

I've seen people use bike cables (like brake cables for caliper brakes) to
create remote actuators for things like hot tub switches where there wasn't
any electrical path between the switch and the tub.

--Chuck
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