PLC?

"Karl Townsend" fired this volley in news:4b1c5b0f$0$77551$ snipped-for-privacy@auth.newsreader.octanews.com:

I think you'll find you don't need any electronics, at all. Most wenches can think (albeit, just a little) on their own. And all have the requisite strength to open and close a roll-up blind.

If the wench can't do the job, fire her and get another. If you're still not pleased, there are all sorts of tiny PLCs out there with most of the requirements a wench could satisfy.

LLoyd

There are some of the little (micro, Pico, Nano) PLC's that have a LCD display and some keys used for configuration. That way you don't need to get programming software, cables, etc.

The Automation Direct PLC looks like it would take programming software and cable.

You can get a couple of 12VDC relays to control your gear motor.

RogerN

I like the price of this one best, its the cheapest. And, Automation Direct has always been good to me. I see the software is free for 100 words max. I have no clue, would this be enough for my application? Room to spare?

Karl

I'm thinking it would. Download the manual and start coding. The documentation should tell you how to count the words you are using.

You might want to look here:

I never got a chance to use one since I the thing I needed done was easy enough to wire up using dicrete relays but it was looking like quite a deal at the time.

Wes

>

I think it would be plenty, not sure if they consider each bit instruction as a word or not.

You want open for a couple of seconds if not on open limit and high temp.

You want close for a couple of seconds in not close limit and low temp.

Another timer could reset the open and close timers if still hot/cold after XX minutes. Maybe if it's hot, opened for a couple of seconds, maybe 15 minutes later if it's still hot open for a couple more seconds.

I'm sure you could get it going in less than 100 words, probably in less than 20 words.

Some of those other PLC's had analog inputs. If you were to use a temperature sensor to an analog input you wouldn't need the thermostats. A thermistor could possibly be used but may need an amplifier to get better resolution.

RogerN

>

Also worth a mention, the more expensive ones have the display and keypad built in. That could be handy for modifying the timers for open/close jog times. With the Automation Direct software you can make the changes but you would have to use a PC. .. Unless you programmed it to change time based on jumpering spare inputs, maybe using spare outputs as indicators.

RogerN

You beat me to it. :-) That sort of spelling just JUMPS out at me for some reason. :-) ...lew...

You should have a field day, then, playing with variations on the idea of Liquid Wench. d8-)

You must lead a boring (or very odd) life if most of your requirements for a wench can be satisfied by a PLC!

Tim Wescott fired this volley in news:xumdnd- UkvHXiIDWnZ2dnUVZ snipped-for-privacy@web-ster.com:

Hell! PLC's can cook and clean, and fetch a beer. For the other things, one can find a 'temporary wench'.

LLoyd

Hey Karl,

A local farmer here won an award very recently for his "high tunnel greenhouse" farming, and here you are doing the same stuff. Local media didn't attempt to explain what is special about it. We buy "retail" from their farm, and I don't see anything different about either the crop or the greenhouses they have, other than maybe an extended season. Lots of agriculture around here under plastic "glass", maybe several hundred acres. Not as much as in the Leamington area, known as the Ontario Sun Belt, where that would be in the thousands of acres I would think. So, in a few short words, can you tell me what a "high tunnel greenhouse" is, and why it is special anyway?

Take care.

Brian Lawson, Bothwell, Ontario.

ps....lot's of older and "NOS" PLCs available on the internet auctions to try. I'd like to give some a go, but the availability of the programmers required is not so easy to find at "that looks like fun" prices.

XXXXXXXXXXXXXXXXXXXX

For some ideas [and to avoid reinventing the wheel] see

google on for c.

21k hits.

also see

?section=17 Please let the group know how things work out.

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Think simple greenhouse exept $/sq.ft. must be lower. Usually no to limited electric. Most important crops are planted in soil. The aim is to produce a crop such as tomato, etc. that harvests much earlier in the season.

Karl

Reminds me of the 3F Rule. If it flies, floats, or f----, rent it. Told to my cousin at a dermatologist's conference by an old thrice divorced attendee.

Pete Keillor

Thanks for all the links. I surfed them and they all seem to violate KISS and cost too much. I've been surfing the web for days on this subject and just came from a growers conference. Nobody (growers) there was using automatic ventilation except the university types.

So far the simplest unit I found costs $700 each (need four per house) and fails if 110 Volt isn't there. I got the mechanical part designed at under $50 per unit that would run days on a deep cycle battery. Control is my weak subject so I'll spend way more time figuring on this.

Karl

--For a good time you might want to mess with a Basic Stamp. Building the circuit and understanding the process will make it much more fun.

There are a number of advantages and disadvantages to this (I was going to suggest it as a last resort).

- per-piece price will be lower, if you can find a home for it in an existing enclosure.

- It'll be way more versatile than a PLC

- It may be harder to wrap your brain around than PLC programming (although maybe not -- relay logic is good if you already do relay logic, but if you're new to it Basic may be better).

- It'll be easier to put a display on it if you want.

In the final analysis, though, my knee-jerk reaction is to avoid PLCs 'cause I've never used one, yet for this project I'd give it serious thought.

Your control rule sounds like it could result in continual oscillation given the right combination of hysteresis, outside temperature, and inside temperature ('continual' in this case being up - wait - down - wait - repeat).

Can you find a dead time that will let these things cycle continuously without draining the batteries, yet will still give you quick enough response when the sun comes out from the clouds or a cold front blows in?

Instead of a fast motion and then a wait, you could use smaller motors geared down more, and just let them grind things open or shut really slowly. This definitely increases the delay and therefore the potential for oscillation without a fancier control rule -- but then you don't have to struggle with the 'wait' logic.

======= This is one of the reasons I suggested using a PC as controller in the links. "Fuzzy logic," to minimize system oscillation/hunting, is relatively easy to implement and the other parameters such as minimum open/closed time are simple to set/vary.

?id=603724 Another reason is the ability for easy expansion to simultaneously control many more inputs, for example not watering during full sun [if that is important].

Inexpensive UPS are now available to maintain the control PC in cases of a power outage.

google on for c 4.7k hits

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).