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John R.
02-21-2007, 11:11 PM
Fellow listers:

I'm working on some automation projects for my aquariums and associated equipment (Reverse osmosis system, water chages, etc.)· Besides the usual sensors for things like temperature, water level, pH, etc., this also involves turning things like lights, pumps, solenoid valves, etc. on and off.

I will be using the Prop and/or SX chips·as processors.

Conceptually, I'm looking at something along the lines of what Tom Sisk (stamptrol) did on this thread, with the probable addition of an LCD and and "human input" panel of some type:

http://forums.parallax.com/showthread.php?p=611540

I am leaning toward using "Opto 22" devices for high voltage i/o, like those shown here:

http://www.opto22.com/site/pr_cat_sc.aspx?qs=100310071003

There are other sources as well.· Parallax used to sell a "carrier board" for similar units.· The ones above are slightly slimmer footprint.

The reasons I'm looking at going this route are:

* My electronics background is weak, and I'm not comfortable selecting descrete components do interface between the logic level and high voltage devices.

* By setting up (or purchasing) a carrier board, I can swap the different types of I/O, including analog input/outputs.

* The actual I/O modules are replaceable, and available from multiple sources.

My questions:

* Am I full of ca-ca (doo-doo)?

* Am I making the selection of descrete components harder that it is?

* As a follow up, for a non-ee type, what process would I use to select descrete componets?· In the·projects I am working on now, input isn't an issue, and the outputs are mostly low current (< 1 Amp) 120 VAC.· Quite frankly, I go and look at Digikey or Mouser, and become "overwhelmed" (as an understatement).· I also have no idea when/if a triac,·FET or other device·is appropriate as opposed to a solid state relay.· I've tried googling, but don't seem to find the right sources of educational information (or have been too impatient...)

* Has anybody made (vs. purchased) a "carrier board" for this type of device, and if so, can you share some information?

Besides the immediate application, and either validation (or not) of my present plan, this is more of a request for "teach me how to know what fish to catch" vs. "tell me what fish to catch".

Thanks for all the help

(Edited URL Links so that they work)

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John R.
Click here to see my Nomad Build Log (http://share.crustcrawler.com/JohnR/)

Post Edited (John R.) : 2/21/2007 7:23:40 PM GMT

stamptrol
02-22-2007, 02:12 AM
John,

You're on the right path. The opto's (and Grayhill's) are a good product and Digikey (plus others) has the required devices and i/o boards.

If you'd like, PM me with what you need to control and I'll generate a parts list.

Cheers,
Tom

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Tom Sisk

http://www.siskconsult.com
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Desy2820
02-22-2007, 05:22 PM
If you just need on/off control of the loads, check these out:

http://www.efx-tek.com/topics/rc-4.html

This board will accept four Solid State Relays, but the relays are sold seperately.· It's controlled as a serial device from the microcontroller, just use SEROUT.· The documentation describes using a "BS-1", but you can also use a BS-2.

I hope this helps!