From: Keith R. Williams
Subject: Re: Alternative design to this?
Date: Mon, 23 Sep 2002 22:13:06 -0400
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
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In article <firstname.lastname@example.org>, email@example.com
> On 20 Sep 2002 18:03:25 -0700, firstname.lastname@example.org (Rich Grise)
> >Tony Williams wrote in message news:<email@example.com>...
> >> In article <firstname.lastname@example.org>,
> >> Peet Grobler wrote:
> >> > What does shift registers do? Maybe I should go find a datasheet and
> >> > have myself a look.
> >> Peet, I have been investigating a remote control
> >> system recently. It does (isolated) remote DAC/ADC,
> >> and digital i/o, all based on a very simple serial
> >> shift register.
> >[excellent art snipped]
> >I just had a thought - you could do it with one wire, with the
> >cheapest microcontroller you can get at each station. When it's
> >energized, it sends its code down the wire. You'd need collision
> >detection, of course, or maybe the PC could send out an "Are you
> >activated?" query, maybe even one per each, and each uC is always
> >listening - when it sees its ID, it sends its state. At first I
> >thought, just one shift register per station - when the switch
> >goes active, you load the shift register, start the clock, and
> >shoot it down the line. But then you've got collisions. Or, you
> >could have a serial-in shift register that's triggered by the
> >above-mentioned interrogation byte, and a comparator. Yup! That's
> >me! And it sends its byte and goes back to listening on the line.
> >Admittedly, with a uC, the parts count is about half of doing
> >it with shift registers and glue. :-)
> Yes... But the cost of the uC is a bit more than the shift registers
> and glue...
Depending on what you're constraints are, a uC may be far less
costly than shift regs and glue. A uC like an 8051 derivative
may be less than a buck. In many cases the uC is there anyway.
Glue is expensive!