Here's the project wiki page: http://openfarmtech.org/index.php?title=Compressed_Air_Water_Pump

This is my discussion with Ralf from Austria about the solenoid timer:

Hi Ralf,

I'm Jeremy with Open Source Ecology (openfarmtech.org)
at Factor e Farm, Marcin recommended I ask you about some stuff on our
compressed air water pump. We need a timer that can allow power through
to the solenoid valve on and off for a short time. It needs to be
adjustable to about 1 second at minimum, with separate on and off
times. We've seen 8 pin and 11 pin things going for about $50-60 but
we're looking for something that's closer to $20-30. Do you have any
ideas? We were possibly considering an arduino if necessary. Thanks for
any feedback.

Take care,

Jeremy 

Hi Jeremy,

Don't know if I fully understand your question, are you looking for a
microcontroller or do you also need an actuator? For the microcontroller
I'd certainly recommend the Arduino: It's an open design with a free and
open development environment. I've used the Arduino in several of my
projects including a chicken door http://blog.runtux.com/2009/01/08/9/
(in german with pictures and links to parts) and a design controlling 3
water valves (240V) for garden watering where I'm using the Arduino to
control the valves via a circuit using an Opto-Triac and a Power Triac
for switching the mains current.

The Arduino has a timer with sub-microsecond resolution, so it should
fit your timing constraints well enough.

I'm mostly using the Duemilanove
http://arduino.cc/en/Main/ArduinoBoardDuemilanove
which has 6 analog inputs and 12 digital input/outputs (programmable if
you're using the pin for input or output). If you don't need the serial
port, you can use two additional input/output pins (0+1 in the photo at
the link above). The I/O Pins marked "PWM" can also use pulse-width
modulation (so these can be used for analog outputs for controlling a
motor for example).

The Duemilanove is around 20.- -- 30.- Euro here in Europe, I don't know
about a source in the US. But even including shipping it should be in
the same price range as the boards you've reviewed.  Last time I ordered
my source was Segor Electronics in Germany, the Duemilanove was 26.20
Euro but that includes 19% VAT.

If you can make your own boards you should be able to make Arduinos for
under 15.- but that only makes sense if you need several. And you need
something to program the initial bootloader. The most expensive part is
probably the USB-to-Serial converter not the Atmega :-)

Concerning the valve: What voltage/current ratings does it have, how are
you going to switch it? If its DC (below 24 V) you should be able to use
an H-Bridge, e.g., a L293D (this is a 16-PIN DIL with two H-Bridges,
if you're only turning Power on/off and don't need to switch direction
(e.g. for a motor) you should be able to control 4 valves with it.
Datasheet: http://www.st.com/stonline/books/pdf/docs/1330.pdf

If it's mains current (110 V in the US I guess), you should be able to
use my approach with a Triac-Circuit, I can mail you the details if
needed.

Ralf

Hi Ralf,

Thanks for the information! Sorry I wasn't more
specific, we already have the solenoid valve which is powered by
110-120 volt AC to open it. Specifically it's an ASCO RedHat II
solenoid valve, like this one: http://cgi.ebay.com/Asco-Red-Hat-II-Solenoid-Valve-8030G003-3%2f4%22-120V-2W-NC_W0QQitemZ250429369333QQcmdZViewItem. It looks like the arduino could be what we need. We could use the details on your triac circuit system, thanks!

Take care,

Jeremy

OK, I've used an opto-triac with zero-crossing detector MOC 3041M
You'll probably want to use the MOC 3031M for 115V Mains
Datasheet is here: http://www.pselectronic.cz/pdf/1114/1114089.pdf
It explicitly mentions solenoid valves :-)

Page 5 of the datasheet has the application circuit diagram for use
with a power triac.

For the power triac I've used the BT 139 / 800 because it just switches
through on overvoltage and doesn't die. You probably won't need a
heatsink since you switch during zero-crossing. And you probably can use
one of the lower-voltage types.
Datasheet:
http://www.nxp.com/acrobat_download/datasheets/BT139_SERIES_4.pdf

Take care -- especially when designing with mains power, what *are* you
up to?

Thanks Ralf!

Check out the initial postand our progress so far:
http://openfarmtech.org/weblog/?p=732
http://openfarmtech.org/weblog/?p=770

Our power is from solar panels to a forklift battery to an inverter
for the whole place here. Once we get the automatic pump done we can
replace the manual pump we have.

I still have to figure out how these things go together, any advice how to learn that?

Thanks,

Jeremy

I see. Great project. I'll do what I can to make this reality.

Can you be a little more specific?
Whats your background in electronics and/or programming?
I'd suggest you learn as you go. I'll try to answer your questions.
Sorry if the following is too trivial for you -- I just don't know what
you're missing :-)

I send you my Arduino program for the water valve (attached), that should
get you an idea how to approach programming the arduino. The development
environment (for windows and linux, i'm not sure about mac) can be
downloaded from arduino.cc. You put that file into its own directory and
point the Arduino software to it as a "sketch" directory (thats the term
arduino is using for its programs).

My design has 3 valves and 3 push-buttons and uses the USB serial from
the arduino for communicating with a host system -- an ASUS WL-500g
premium router running the OpenWRT linux distribution
http://oldwiki.openwrt.org/OpenWrtDocs(2f)Hardware(2f)Asus(2f)WL500GP.html
With this I can turn on/off water with a wireless connection from my
notebook :-)

I'm also attaching an arduino library "timer" used by my water valve
project that provides you with a nice interface to the arduino timer and
can debounce buttons (when there is a very short spike on the power
line, the arduino sometimes "thinks" that a button has been pressed, for
this I'm reading a button several times to be sure that it was really
pressed).

Before doing anything complex though, you should get familiar with the
arduino environment.

For trying out the program, you can connect a LED to the output-pin of
the arduino where you later connect the triac circuit for switching the
pump. You'll use a 470 Ohm Resistor in series with the LED:

                           +-------+     +\
Arduino output-PIN ---------+       +-----+  >---------- Ground
                           +-------+     +/

With this you can test your program.

There is one led already on the arduino, connected in parallel to output
pin 13, you can use this to get a feeling for arduino programming
without any external hardware.

Then you need to build the triac circuit. I'm using ready-made
experimentation boards similar to that one:
http://shop.conrad.at/ce/de/product/521140/LOeTSTREIFENRASTERPLATTE715HP160x100
with a raster of 2.54mm (.1in I think), thats what you need for ICs in
DIP packaging. You solder the IC and remove the copper with a 3mm drill
where you dont need it, e.g.,

                            +     +
XXXXXXXXXXXXXXXXXXXXXXXXXXXX +  D  + XXXXXXXXXXXXXXXXXXXX Copper
                            +     +

The '+' show the soldering-spots for an IC, the XXX is a copper line on
the board. You use the drill at the position "D" to just remove the
copper at that position (don't drill a hole!). With that you don't need
to etch your own circuit boards, which is much faster if you only build
one unit.

Then you use isolated copper a hookup wire (sorry if I don't get the
right word here, the german word is "Schaltdraht", you can see what I
mean, look at the green wires in the picture "Mechanischer Aufbau" at
http://blog.runtux.com/2009/01/08/9/) to connect the arduino to your
circuit. You can just stick the wires into the arduino connectors, that
should be enough for prototyping and my chicken door is running for more
than half a year now with these connections. You can either solder the
other end of the wires to your board or use connectors. Connectors are
better if you want to remove your board later, I've used connectors for
the chicken door electronics (the H-Bridge L293D I've mentioned earlier)
Have someone else double-check the circuit before connecting mains
power! Be sure to use proper grounding etc for the chassis of the
electronics, especially when doing something with water you'll *need* a
watertight chassis!

I think we should start documenting this in the wiki and/or use a
mailinglist, so others can join in, what do you think? Especially the
parts and sources in the US would probably be of much value to others
trying your designs.

Thanks! I'm starting to see how the stuff goes together. I have some
programming experience with scripting languages and python so I can see
the basic function of the code but I still have a lot to learn. I don't
have much electronics experience so I'll have to figure it out as I
work on this project. I think it's a good idea to move the conversation
to somewhere for documentation, let's use the wiki. Shall I copy the
conversation so far to the water pump discussion page (http://openfarmtech.org/index.php?title=Talk:Compressed_Air_Water_Pump) and we can continue there?

Jeremy

Fine, I'm also doing most projects in python.

Hmm, for me a wiki isn't a very good discussion forum -- I have tried
several times to poll a wiki regularly and so far always failed :-)
lets continue the discussion via email and once we have a mailinglist --
I've just ordered a Hetzner.de server where we can host one or we could
host it on your server -- we repost our discussion there so it gets
archived. Later on when everything is in place, somebody may want to
distill a wiki page from it, what do you think?

I've no objection, though if you want to start documenting on the wiki.

Alright, we could also use the forum (http://factorefarm.org/forum) or a blog post (http://openfarmtech.org/weblog/).
What are the advantages of using a mailing list over the forum? And by
mailing list you mean something like the yahoo groups or google groups
things? I'll make a forum post on it for now.

Thanks again for your help!