On 10/14/2006 1:07 PM, Richard W. Ernst wrote:
Barry Gershenfeld wrote:
A mechanical actuator has something like a clock motor with cams that
push electrical contacts together--you can't do much with that except
maybe make the motor run faster or stop it. Remember Armitron? A
robot arm toy. That turned out to be cams and levers inside. Or
consider animating a manual typewriter (not that any of us ever did
*that*).
A relay can be controlled by switching a current on and off. So, you
just rip out the factory brains, and drop in your own. Because the
factory designed the right electronics to drive the valves for
you--and they give you a proper power supply along with it. (Assuming
you trust the factory design...from people who name their stuff
"Ecxtra"...) What I call the "brains" just decides *when* to open
the valves.
As nobody was willing to touch "sun synchronous" :-) What happened
here was that I am aware that micros don't keep very good time, unless
you add some more hardware. So I thought, with a light sensor, you
could watch the sun rise and set, and that would be close enough.
I think you're the ONLY one who thought Joe's project was related to the
subject.... :)
got the difference re: actuator and relay now. It's electronic with
relays (I'm assuming relays).
as for naming, I suspect the engineer that gets to name the final
product is VERY rare... or we'd have cats named gizmo, or websites
named google. Oops, that is a website... :)
Again, I did miss your meaning of "sun synchronous". I suppose I could
hook a sun dial to it... :) I've no idea what cpu it runs inside, but
there's a reminder setting you can vary to check your own settings
(software utilizes internet for weather averages, temp, humidity and
wind), I suspect it'd get re-sync'd any time you re-connected the
updated interface.
and, of course, my crippled (no idea what's wrong at this point) Windows
XP won't recognize the USB part of this thing, so now I'll have to fixt
THAT before I can program it... :)
Sorry I'm coming into this way after the thread has gone another way and
come back. FWIW, here's my input. I think in hardware, so that's where
this is headed.
I've worked with several commercial sprinkler controllers (non
computer-controlled) and have about a dozen valves operated by three
controllers. The shortcomings I see with commercial controllers are
software, software, and software. Made to be set up by gardeners, with
severe lack of flexibility in programming. Building a
computer-controlled one has been on my mind for years.
The commercial controllers I've used have a 24-volt AC transformer and
an SCR to drive each vzlve. There is a fuse in case of a short in the
wiring. To connect a computer to the valves you would probably want
some kind of isolation (optical or relay). The serial interface would
be quite simple from a hardware design point. I would bit-bang the
interface -- have one line as the serial data line, one as the clock and
another as the latch. No need for speed here, send the data out slowly
to improve noise immunity. Use the handshaking lines of the serial port
for clock and data. Use TxD as the latch.
I would dedicate an old computer (Pentium I?) running Linux. These take
about 25 watts continuous, less if you do network boot with no hard
disk. Program it in whatever language you want, so long as it can talk
to the serial port. Use a text file for config, have the program that
does the work read it each time it runs (cron job). Locate it in the
garage or wherever is close to your sprinkler valves, and program it
from elsewhere.
So, for each channel (or station, sprinkler-controller parlance) you
would need one isolator and one SCR. And serial-to-parallel converters
(shift registers). Those come 8 channels to a chip, and you can string
together as many as you want by lengthening the serial word that you
send out. A few odd components, a 24-volt AC transformer for each
station you want on simultaneously, put it in a box, and you're done.
Karl
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