My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will be
ventilating by using a rollup side curtain. I plan to automate the process
by using a small 12 volt DC gear motor and wench. I've settled on my
mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few seconds
and go to delay timer. If you make Lo unroll a few seconds and go to delay
timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there an
inexpensive simple to program unit that runs on 12 volt DC? Alternatively, I
can see a way to do it with a timer that continuously does a few seconds on
then several minutes off continuously.

Karl

"Karl Townsend" fired this volley in
anews.com:


I'm thinking this is PLC territory. I know nothing about them. Is
there an inexpensive simple to program unit that runs on 12 volt DC?
Alternatively, I can see a way to do it with a timer that continuously
does a few seconds on then several minutes off continuously.


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.

http://www.softwarecorp.com/FX2N14.htm

http://www.ab.com/programmablecontro...ontroller.html

http://www.automationdirect.com/adc/...nits/D0-05DR-D

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

http://www.automationdirect.com/adc/...nits/D0-05DR-D

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

"Karl Townsend" wrote:

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?

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 he
http://www.bb-elec.com/product_multi...TrailType=Main

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

--

"Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Running Light without
Overbyte".

"Karl Townsend" wrote in message
anews.com...
http://www.automationdirect.com/adc/...nits/D0-05DR-D

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 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

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


On Sun, 6 Dec 2009 19:31:56 -0600, "Karl Townsend"
wrote:

My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will be
ventilating by using a rollup side curtain. I plan to automate the process
by using a small 12 volt DC gear motor and wench. I've settled on my
mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few seconds
and go to delay timer. If you make Lo unroll a few seconds and go to delay
timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there an
inexpensive simple to program unit that runs on 12 volt DC? Alternatively, I
can see a way to do it with a timer that continuously does a few seconds on
then several minutes off continuously.

Karl

"Brian Lawson" wrote in message
...
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?

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

On Mon, 7 Dec 2009 10:09:26 -0600, "Karl Townsend"
wrote:


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


Yabbut what's the difference between "High tunnel" and plain ordinary
polytunnel greenhouses?

Expiring minds want to know :-)

Mark Rand
RTFM

"Mark Rand" wrote in message
...
On Mon, 7 Dec 2009 10:09:26 -0600, "Karl Townsend"
wrote:


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


Yabbut what's the difference between "High tunnel" and plain ordinary
polytunnel greenhouses?

Expiring minds want to know :-)

Mark Rand
RTFM

If you're looking at the structure the difference is blurred. Few
greenhouses use natural ventilation - large exhaust fans. most high tunnel
have huge natural vent opening.

The main difference is application. Greenhouse grow plant for resale in some
sort of medium normally on shelves. High tunnel grows fruit and vegetables
in the soil.

Karl

On Tue, 8 Dec 2009 20:54:22 -0600, "Karl Townsend"
wrote:


"Mark Rand" wrote in message
.. .
On Mon, 7 Dec 2009 10:09:26 -0600, "Karl Townsend"
wrote:


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


Yabbut what's the difference between "High tunnel" and plain ordinary
polytunnel greenhouses?

Expiring minds want to know :-)

Mark Rand
RTFM

If you're looking at the structure the difference is blurred. Few
greenhouses use natural ventilation - large exhaust fans. most high tunnel
have huge natural vent opening.

The main difference is application. Greenhouse grow plant for resale in some
sort of medium normally on shelves. High tunnel grows fruit and vegetables
in the soil.

Karl



Ok, That's what I'd know as polytunnels (not the same as the home vegetable
plot variety though...)


regards
Mark Rand
RTFM

On Tue, 08 Dec 2009 23:47:38 +0000, the infamous Mark Rand
scrawled the following:

On Mon, 7 Dec 2009 10:09:26 -0600, "Karl Townsend"
wrote:


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


Yabbut what's the difference between "High tunnel" and plain ordinary
polytunnel greenhouses?

Expiring minds want to know :-)

Who cares? With your feared AGWK, you'll soon be able to grow
tomatoes Over There, too!

--
To know what you prefer instead of humbly saying Amen
to what the world tells you you ought to prefer,
is to have kept your soul alive.
-- Robert Louis Stevenson

--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.


--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---

On Mon, 07 Dec 2009 18:39:57 +0000, steamer wrote:

--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.

--
www.wescottdesign.com

--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.

I actually hate PLCs, never got on with ladder logic very well. I'm much
more comfortable with computer programming. Are we talking about a PIC chip
here, like a 16f628A/16f877A?

Would either you or Steamer be willing to get me started with what hardware
to order? And stuff to start reading?

Karl

On Mon, 07 Dec 2009 15:08:44 -0600, Karl Townsend wrote:

--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.

I actually hate PLCs, never got on with ladder logic very well. I'm much
more comfortable with computer programming. Are we talking about a PIC
chip here, like a 16f628A/16f877A?

Would either you or Steamer be willing to get me started with what
hardware to order? And stuff to start reading?

Karl

Do you want to program in Basic, assembly, or C?

For Basic, you want to get a Basic Stamp -- these have a PIC on them, but
it's hidden behind a layer of programming, so what you see is Basic.
They're sold by Parallax, who is not pushing their "propeller" chip,
which I can't find it in my heart to recommend because it uses a
proprietary compiler, and those always end up burning you in the end.

For assembly or C you (probably) want to get a PicKit (SP?) designed by
Microchip. They have what you need to get a basic computer up an
running, and Microchip at least used to have a free C compiler for some
of their computers.

I wouldn't recommend the C or assembly route unless you have some serious
programming experience under your belt. C and assembly are each the
programming equivalent of a manual lathe -- you can do anything possible
with them, but you have a lot to learn before you can start doing
anything useful with them.

_Any_ of these routes will get you a board that only drives logic levels
out, and will leave you responsible for all of the surrounding drive
electronics to turn it into motor commands and protection to keep it from
going up in smoke during the first lightning storm. A PLC is much more
likely to have some useful drive capability built in.

Look to the Parallax website and SparkFun electronics for neato modules
that you can assemble into a working system. Used wisely, you should be
able to get away without having to design a board, at least for the
prototype system.

--
www.wescottdesign.com

Karl Townsend wrote:
Would either you or Steamer be willing to get me started with what hardware
to order? And stuff to start reading?
--Parallax has a kit consisting of everything you'll need to get
started and to get a solid understanding of what's going on. The book's
called "What's a Microcontroller" and it comes with a kit of parts that are
very well thought out. I had a UC Extension class called "Gizmology" that
used this material and it was a real eye-opener; I've used it to make a
pneumatic tapdancing robot (pretty primitive but it worked!) and lately I've
used it to drive my calliope.
--Reason I like the Stamp: they've got the most comprehensive manual
and it assumes you know NOTHING when you start out; something sadly lacking
from all the other systems I've encountered..
--You'll want to start he
http://www.parallax.com/Default.aspx?tabid=362
Ping me off list ifyawanna know more. And they have a forum at:
http://forums.parallax.com/forums/
--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---

Would either you or Steamer be willing to get me started with what
hardware
to order? And stuff to start reading?
--Parallax has a kit consisting of everything you'll need to get
started and to get a solid understanding of what's going on. The book's
called "What's a Microcontroller" and it comes with a kit of parts that
are
very well thought out. I had a UC Extension class called "Gizmology" that
used this material and it was a real eye-opener; I've used it to make a
pneumatic tapdancing robot (pretty primitive but it worked!) and lately
I've
used it to drive my calliope.
--Reason I like the Stamp: they've got the most comprehensive manual
and it assumes you know NOTHING when you start out; something sadly
lacking
from all the other systems I've encountered..
--You'll want to start he
http://www.parallax.com/Default.aspx?tabid=362
Ping me off list ifyawanna know more. And they have a forum at:
http://forums.parallax.com/forums/
--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---

Thanks for the advice. I ordered their starter kit and plan to spend several
weeks with it right after Christmas. If these can play a calliope they must
be "good stuff Maynard"

Karl

Tim Wescott wrote:


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.


Plc's are great. I had a couple 600 ton St Lawrence forming presses with about 22 control
relays, 5 cycleflex counters or timers that would not stay running.

Took a class at Allen Bradley on programming a plc and in 43 rungs of logic, I replaced
that mess and kept us from shutting down a GM assembly plant.


Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

On Sun, 06 Dec 2009 19:31:56 -0600, Karl Townsend wrote:

My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will
be ventilating by using a rollup side curtain. I plan to automate the
process by using a small 12 volt DC gear motor and wench. I've settled
on my mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few
seconds and go to delay timer. If you make Lo unroll a few seconds and
go to delay timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there
an inexpensive simple to program unit that runs on 12 volt DC?
Alternatively, I can see a way to do it with a timer that continuously
does a few seconds on then several minutes off continuously.

Karl

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.

--
www.wescottdesign.com

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.

You described the exact issue. Mechanically, I've got it geared down to
raise/lower 12"/minute with a total travel of 60 inches. Gets hard to gear
it much slower. My "plan A" is two stats so you have a dead band, then play
with % run to get response without oscillation. I suppose if you knew
exactly what percent on/off was optimum you could just gear it for 100% on.

I'm intrigued with this analog input option on a PLC. I should be able to
use a higher percent on when farther from temp target. The high end computer
systems you see on university research houses do this.

Karl

On Mon, 07 Dec 2009 13:56:56 -0600, Karl Townsend wrote:

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.

You described the exact issue. Mechanically, I've got it geared down to
raise/lower 12"/minute with a total travel of 60 inches. Gets hard to
gear it much slower. My "plan A" is two stats so you have a dead band,
then play with % run to get response without oscillation. I suppose if
you knew exactly what percent on/off was optimum you could just gear it
for 100% on.

If only...

I suspect that the optimum percentage will vary depending on the
difference between inside and outside temperature. You're essentially
setting up a temperature control system that has a constant heat input
(from the sun), and variable heat shedding (the vents). But the amount
of heat shedding that you get at any one moment is dependent not only on
the amount that the vents are open, but on the outside temperature and (I
suspect) on the amount of wind.

So the interior temperature delta that you'll see for 1" of opening will
be much bigger on a windy deep-winter day than it will on a mild day in
the spring.

This points to either needing to change your tuning manually with the
season, needing to have an external thermometer that you use to select a
control rule, some sort of adaptive controller, a heavily compromised
control rule that guarantees stability on bad days at the cost of being
really sluggish on good days, or just a happy acceptance of the fact that
your motors are always moving, but your greenhouses are always at a good
temperature and generating money.

I'm intrigued with this analog input option on a PLC. I should be able
to use a higher percent on when farther from temp target. The high end
computer systems you see on university research houses do this.

If you want to go there, let me suggest _right now_ that you forget the
PLC approach and lean toward using a PC or a Basic Stamp -- or find a PLC
that uses a real programming language. Unless you want to spend your
time working around the limitations of your controller instead of solving
your problem, you want to start out with a controller that is way more
capable than you think you need -- because with control loops, you
_always_ end up needing more smarts in the controller than you thought
when you started.

I still have this problem, and I've been doing it for 20 years. If you
look at your controller's capabilities and say "that's about right" then
you're severely undershooting your goal.

This is actually an odd case, because while I'm thinking of this as if
you were a client, I wouldn't necessarily take my own advice if I were
doing it myself. Were I doing this for myself I'd start with the simple
route that you have proposed or something close, see how it works, and be
ready to improve on it next winter. You'll learn so much about the
dependability of your mechanical arrangement, the sufficiency of your
batteries, plus all the stuff that no one has anticipated even thinking
about yet.

But if you were paying me to get it working I wouldn't do that. Instead
I'd either walk or I'd get all complex (and expensive) on you. Why?
Because when you engineer a system that shows promise but doesn't make
the customer money, they don't remember the joy of your low-ball bill --
they just remember that you built them a system that didn't @#$% work!

--
www.wescottdesign.com

....
If you want to go there, let me suggest _right now_ that you forget the
PLC approach and lean toward using a PC or a Basic Stamp -- or find a PLC
that uses a real programming language. Unless you want to spend your
time working around the limitations of your controller instead of solving
your problem, you want to start out with a controller that is way more
capable than you think you need -- because with control loops, you
_always_ end up needing more smarts in the controller than you thought
when you started.

I still have this problem, and I've been doing it for 20 years. If you
look at your controller's capabilities and say "that's about right" then
you're severely undershooting your goal.

This is actually an odd case, because while I'm thinking of this as if
you were a client, I wouldn't necessarily take my own advice if I were
doing it myself. Were I doing this for myself I'd start with the simple
route that you have proposed or something close, see how it works, and be
ready to improve on it next winter. You'll learn so much about the
dependability of your mechanical arrangement, the sufficiency of your
batteries, plus all the stuff that no one has anticipated even thinking
about yet.

But if you were paying me to get it working I wouldn't do that. Instead
I'd either walk or I'd get all complex (and expensive) on you. Why?
Because when you engineer a system that shows promise but doesn't make
the customer money, they don't remember the joy of your low-ball bill --
they just remember that you built them a system that didn't @#$% work!

Your last paragraph explains why a gear motor on a thermostat is going for
$700 a copy. its going to take some fool willing to have a few failures to
come up with a $100 solution.

OK, I'm sold on trying this basic stamp approach. Sure could use some help
on what items to purchase. I don't mind spending a few (several) weeks
learning a new subject.

Karl

Karl Townsend wrote:
...

But if you were paying me to get it working I wouldn't do that. Instead
I'd either walk or I'd get all complex (and expensive) on you. Why?
Because when you engineer a system that shows promise but doesn't make
the customer money, they don't remember the joy of your low-ball bill --
they just remember that you built them a system that didn't @#$% work!

Your last paragraph explains why a gear motor on a thermostat is going for
$700 a copy. its going to take some fool willing to have a few failures to
come up with a $100 solution.

OK, I'm sold on trying this basic stamp approach. Sure could use some help
on what items to purchase. I don't mind spending a few (several) weeks
learning a new subject.

Karl


There are a bunch of tiny little control processors on the market today.

For what you want to do, the BASIC stamp would probably be the best choice.

Start with Wiki for a good overviwew:
http://en.wikipedia.org/wiki/BASIC_Stamp

More involved:
http://www.parallax.com/tabid/295/Default.aspx

Best place to get started with the Stamp would be the Activity Kit.
(that's probably gonna wrap)
http://www.parallax.com/Store/Microc...me,ProductName

Example Projects:
http://www.rentron.com/BasicStamp.htm
Relay control example:
http://www.rentron.com/pc-relay.htm

http://www.emesystems.com/BS2index.htm

Development and info downloads:
(including Stamp and application manuals)
http://webspace.webring.com/people/a...downloads.html

"Karl Townsend" fired this volley in
anews.com:

I'm intrigued with this analog input option on a PLC. I should be able
to use a higher percent on when farther from temp target. The high end
computer systems you see on university research houses do this.


You're describing a PID (proportional-integral-derivative) control
system, which, despite being described as "fuzzy logic", is not -- it's a
software emulation of an analog, variable gain, proportional output
system.

Most decent PLCs have freely-available PID loop software available for
them. If you use one of the sorts that allows easy user programming
(usually via both ladder logic and a crippled sort of BASIC) you can
easily set one up for PID control.

You'll need to modify the curtain controller from simply on/off to a
position-sensing controller to make best use of such a system.

I'm not sure they're in the price range you'd like to spend (although
pretty cheap), but the TriLogic PLCs are both capable and easy to program
with free software that comes with them. I have a three NC machines
(dedicated automated machinery for manufacturing fireworks) operating
under control of the TriLogic boards, and have not a single breakdown in
seven years of operation (totalling 21 controller-years, 40-60 hours a
week, year-round).

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com fired this volley in
. 3.70:

Most decent PLCs have freely-available PID loop software available for
them.

oops! Forgot to say, the TriLogic boards have some user-devised, free PID
samples to play with.

LLoyd

"Karl Townsend" wrote in message
anews.com...


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.

You described the exact issue. Mechanically, I've got it geared down to
raise/lower 12"/minute with a total travel of 60 inches. Gets hard to gear
it much slower. My "plan A" is two stats so you have a dead band, then
play with % run to get response without oscillation. I suppose if you knew
exactly what percent on/off was optimum you could just gear it for 100%
on.

I'm intrigued with this analog input option on a PLC. I should be able to
use a higher percent on when farther from temp target. The high end
computer systems you see on university research houses do this.

Karl



A very cheap contol system would be 2 cheap snap acting home thermostats - 1
mounted high and 1 mounted low, although you might have to monkey with the
location. You can still get units that come with an available proportional
band adjustment, not much but usually 2-6 deg.F. Set 1 for cooling and 1
for heating. They boot up from power failure every time the power returns.

Good luck
Steve

"Karl Townsend" wrote in message
tanews.com...


You described the exact issue. Mechanically, I've got it geared down to
raise/lower 12"/minute with a total travel of 60 inches. Gets hard to gear
it much slower. My "plan A" is two stats so you have a dead band, then
play with % run to get response without oscillation. I suppose if you knew
exactly what percent on/off was optimum you could just gear it for 100%
on.

You can't know that because it will change significantly with cloud
cover, sun angle, wind, etc.

On Tue, 08 Dec 2009 22:06:17 -0600, Don Foreman
wrote:




"Karl Townsend" wrote in message
ctanews.com...


You described the exact issue. Mechanically, I've got it geared down to
raise/lower 12"/minute with a total travel of 60 inches. Gets hard to gear
it much slower. My "plan A" is two stats so you have a dead band, then
play with % run to get response without oscillation. I suppose if you knew
exactly what percent on/off was optimum you could just gear it for 100%
on.

You can't know that because it will change significantly with cloud
cover, sun angle, wind, etc.




It ain't hard, it just ain't cheap. I used a double reduction
Sumitomo cycloid drive of 3400:1 to drive the continuous filter I
invented. Web movement maximum was 60"/hour, min was close to zero.
I'd mark the web, go have a cup of coffee, come back and stick a ruler
on it to make sure it was working.

Pete Keillor

What's that Lassie? You say that Karl Townsend fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by Sun, 6 Dec 2009 19:31:56 -0600:

I plan to automate the process
by using a small 12 volt DC gear motor and wench. I've settled on my
mechanical design and plan to order parts tomorrow.

You can make an analog-ish controller to do what you want.

I had good results using two small audio amplifiers as a servo drive
to power a small gearmotor. For your project I would stick to relay
control of the motor though. If you got two standard thermostats,
and a few relays, I think you would have it.

Look at :http://www.redrok.com/electron.htm for some ideas.

If you could rig a potentiometer with the curtain, then you could have
proportional control. That is, the hotter it is, the more open the
curtain is. With the right gain, it should hold temperature well.
--

Dan H.
northshore MA.

"Karl Townsend" wrote
My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I
will be ventilating by using a rollup side curtain. I plan to
automate the process by using a small 12 volt DC gear motor and
wench. I've settled on my mechanical design and plan to order parts
tomorrow.

My query is on control. KISS is the order of the day here. I plan on
two thermostats - Hi and Lo. Also two limit switches - full open and
full closed. The control is simple - if you make Hi; roll up for a
few seconds and go to delay timer. If you make Lo unroll a few
seconds and go to delay timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is
there an inexpensive simple to program unit that runs on 12 volt DC?
Alternatively, I can see a way to do it with a timer that
continuously does a few seconds on then several minutes off
continuously.

If your goal is KISS, skip the PLC and try something like this:
http://search.digikey.com/scripts/Dk...&name=Z2695-ND

all the control logic is built in. the alarm can be used to revers the
direction of the motor.

Lots of manufacturers out there with similar options.

On Sun, 06 Dec 2009 19:31:56 -0600, Karl Townsend wrote:

My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will
be ventilating by using a rollup side curtain. I plan to automate the
process by using a small 12 volt DC gear motor and wench. I've settled
on my mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few
seconds and go to delay timer. If you make Lo unroll a few seconds and
go to delay timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there
an inexpensive simple to program unit that runs on 12 volt DC?
Alternatively, I can see a way to do it with a timer that continuously
does a few seconds on then several minutes off continuously.

Karl

The more I think about this the more I think you want the roll-up curtain
to roll down over a tapered hole, so that when you're closed you don't
get as much area change as when you're open -- because a given area
change will be much more effective when it's cold and the curtains are
closed up, and because once the curtains are mostly open a bit more isn't
going to change much.

Just a thought, but get it working first.

--
www.wescottdesign.com

On Sun, 6 Dec 2009 19:31:56 -0600, "Karl Townsend"
wrote:

My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will be
ventilating by using a rollup side curtain. I plan to automate the process
by using a small 12 volt DC gear motor and wench. I've settled on my
mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few seconds
and go to delay timer. If you make Lo unroll a few seconds and go to delay
timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there an
inexpensive simple to program unit that runs on 12 volt DC? Alternatively, I
can see a way to do it with a timer that continuously does a few seconds on
then several minutes off continuously.

Karl

If outdoor temp is higher than your minimum, if the temp ever got high
enough to open the curtain it'd stay open until outdoor temp drops.

If outdoor temp is lower than your min but there's enough sun to heat
the space to above max with curtain closed, then the system would
cycle, alternately opening and closing.

If outdoor temp is lower than min and there's not enough sun to reach
max temp, then the curtain would stay closed.

If you only partially move the curtain and then go to a delay timer
for a while to see if that move drops temp below max, might it take
unacceptably long to fully open on a high temp condition? The time
constant will be quite different on calm days vs windy days.

A PID controller with a temperature sensor would provide better
temperature stability, but at the expense of battery life because the
curtain would be making small moves very often. You'd need curtain
position feedback too.

"Don Foreman" wrote in message
...
On Sun, 6 Dec 2009 19:31:56 -0600, "Karl Townsend"
wrote:

My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will be
ventilating by using a rollup side curtain. I plan to automate the process
by using a small 12 volt DC gear motor and wench. I've settled on my
mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few seconds
and go to delay timer. If you make Lo unroll a few seconds and go to delay
timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there an
inexpensive simple to program unit that runs on 12 volt DC? Alternatively,
I
can see a way to do it with a timer that continuously does a few seconds
on
then several minutes off continuously.

Karl

If outdoor temp is higher than your minimum, if the temp ever got high
enough to open the curtain it'd stay open until outdoor temp drops.

If outdoor temp is lower than your min but there's enough sun to heat
the space to above max with curtain closed, then the system would
cycle, alternately opening and closing.

If outdoor temp is lower than min and there's not enough sun to reach
max temp, then the curtain would stay closed.

If you only partially move the curtain and then go to a delay timer
for a while to see if that move drops temp below max, might it take
unacceptably long to fully open on a high temp condition? The time
constant will be quite different on calm days vs windy days.

A PID controller with a temperature sensor would provide better
temperature stability, but at the expense of battery life because the
curtain would be making small moves very often. You'd need curtain
position feedback too.


I was wondering if he could use a string pot on the curtain for position
feedback? I've never eBayed for them but I don't think they are very cheap
new.

RogerN

RogerN wrote:
"Don Foreman" wrote in message
...
On Sun, 6 Dec 2009 19:31:56 -0600, "Karl Townsend"
wrote:

My first winter project is on my new high tunnel (greenhouse) High
temperature control by ventilation is critical for good growing. I will be
ventilating by using a rollup side curtain. I plan to automate the process
by using a small 12 volt DC gear motor and wench. I've settled on my
mechanical design and plan to order parts tomorrow.

My query is on control. KISS is the order of the day here. I plan on two
thermostats - Hi and Lo. Also two limit switches - full open and full
closed. The control is simple - if you make Hi; roll up for a few seconds
and go to delay timer. If you make Lo unroll a few seconds and go to delay
timer. Stop on limit switches. Repeat 24X7.

I'm thinking this is PLC territory. I know nothing about them. Is there an
inexpensive simple to program unit that runs on 12 volt DC? Alternatively,
I
can see a way to do it with a timer that continuously does a few seconds
on
then several minutes off continuously.

Karl
If outdoor temp is higher than your minimum, if the temp ever got high
enough to open the curtain it'd stay open until outdoor temp drops.

If outdoor temp is lower than your min but there's enough sun to heat
the space to above max with curtain closed, then the system would
cycle, alternately opening and closing.

If outdoor temp is lower than min and there's not enough sun to reach
max temp, then the curtain would stay closed.

If you only partially move the curtain and then go to a delay timer
for a while to see if that move drops temp below max, might it take
unacceptably long to fully open on a high temp condition? The time
constant will be quite different on calm days vs windy days.

A PID controller with a temperature sensor would provide better
temperature stability, but at the expense of battery life because the
curtain would be making small moves very often. You'd need curtain
position feedback too.


I was wondering if he could use a string pot on the curtain for position
feedback? I've never eBayed for them but I don't think they are very cheap
new.

RogerN




I would think a simple timing loop would do it.
Run the device and see how long it takes to go from one end
to the other. Divide that by 256 for max resolution, or more
likely by 16 - plenty of resolution for a vent.

I would like to see limit switches at each end just for safety sake.
That would take up two bits of input per vent.
But if the device has comfortable "over-run" areas, it might not be needed.

In article ,
cavelamb wrote:

[snip]

I would like to see limit switches at each end just for safety sake.
That would take up two bits of input per vent.
But if the device has comfortable "over-run" areas, it might not be needed.

I agree that limit switches are needed, but they should physically
interrupt power to the motor, and in no way depend on software.

The problem is that once these limits are hit, the computer can no
longer recover control, and a manual reset is needed.

The usual solution is to have two sets of limit switches, inner and
outer.

The inner limit switches are sensed by the computer, telling it to stop
moving in that direction.

The outer set physically interrupts power to the motor, to prevent
damage should the computer fail to do the right thing.

Joe Gwinn

Joseph Gwinn wrote:
In article ,
cavelamb wrote:

[snip]
I would like to see limit switches at each end just for safety sake.
That would take up two bits of input per vent.
But if the device has comfortable "over-run" areas, it might not be needed.

I agree that limit switches are needed, but they should physically
interrupt power to the motor, and in no way depend on software.

The problem is that once these limits are hit, the computer can no
longer recover control, and a manual reset is needed.

The usual solution is to have two sets of limit switches, inner and
outer.

The inner limit switches are sensed by the computer, telling it to stop
moving in that direction.

The outer set physically interrupts power to the motor, to prevent
damage should the computer fail to do the right thing.

Joe Gwinn


There is an old saying that,
"If engineers built bridges the way programmers write software,
the first wood pecker than comes along could destroy civilization".

And there is some truth in that.

But no, I'd not design an autonomous system that need manual oversight.

IIRC, Karl said his vent was about 6 feet long.

My first fantasy was a fabric tape/shade (wide enough to cover the vent slot)
that rolls up on rollers at each end. Maybe it has some shaped supports
to keep it snug against the enclosure(?). But there is nothing to jam into
at the end of the run.

So all I'd be doing is rolling the shade up or down.

The computer can monitor the drum and tell, within reason, where the opening
is at any time. If we are rolling up on a fairly small shaft, just count
turns. If it's a big drum, maybe glue some magnets around the drum and count
them with a Hall effect sensor.

You don't see that kind of proactive defense in other mechanical devices.
Printers, Plotters, Flight simulator motion platforms, CARS.

But you do have to be careful about writing any wood peckers into your code.


Richard

On Wed, 09 Dec 2009 09:06:23 -0500, Joseph Gwinn wrote:

In article ,
cavelamb wrote:

[snip]

I would like to see limit switches at each end just for safety sake.
That would take up two bits of input per vent. But if the device has
comfortable "over-run" areas, it might not be needed.

I agree that limit switches are needed, but they should physically
interrupt power to the motor, and in no way depend on software.

The problem is that once these limits are hit, the computer can no
longer recover control, and a manual reset is needed.

The usual solution is to have two sets of limit switches, inner and
outer.

The inner limit switches are sensed by the computer, telling it to stop
moving in that direction.

The outer set physically interrupts power to the motor, to prevent
damage should the computer fail to do the right thing.

Joe Gwinn

With a DC system it's easy to set up limit switches that'll prevent a
motor from driving any further into a stop, but will let it drive out.

And even though I write embedded code, too, I still prefer to have
mechanical safety devices -- for when someone else starts maintaining my
bug-free code, of course.

--
www.wescottdesign.com

Joseph Gwinn wrote:

In article ,
cavelamb wrote:

[snip]

I would like to see limit switches at each end just for safety sake.
That would take up two bits of input per vent.
But if the device has comfortable "over-run" areas, it might not be needed.

I agree that limit switches are needed, but they should physically
interrupt power to the motor, and in no way depend on software.

The problem is that once these limits are hit, the computer can no
longer recover control, and a manual reset is needed.


Diodes across the limit switch, so it can only run the other
direction. This was common on Sat dish steering motors, and trailer
jacks. You hit the limit, and the switch opens, but the diode will allow
it to be backed off.



The usual solution is to have two sets of limit switches, inner and
outer.

The inner limit switches are sensed by the computer, telling it to stop
moving in that direction.

The outer set physically interrupts power to the motor, to prevent
damage should the computer fail to do the right thing.

Joe Gwinn


--
Offworld checks no longer accepted!

What's that Lassie? You say that cavelamb fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by Wed, 09 Dec 2009 05:52:45 -0600:

I would like to see limit switches at each end just for safety sake.
That would take up two bits of input per vent.

Not nessarly. If you are using a DC motor, just cut the power with
the switches. Add a diode across the switch so the motor can reverse
off the limit.
--

Dan H.
northshore MA.