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Sprinkler pump controller

Discussion in 'Electronic Design' started by [email protected], Mar 18, 2007.

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  1. Guest

    I've had this idea for a while but don't know exactly how to go
    about it. I'm thinking of a micro controller of some sort but I
    haven't worked with micro controllers and not sure which one would be
    best for this project. I also want to make this project into
    something that I could use on a resume, something . I am an
    electronics engineering technician (AS-ET).

    This is the basics of what I have now. I have a water retention
    system (55 gallon drums manifold together) that has an MPXV501GP (1.45
    PSI) to detect the water level in the system. I have a rain sensor
    mounted on the gutter.

    What I want to be able to do is to turn on the sprinkler pump
    after it hasn't rained for a number of days. I also want the pump to
    come on when the system level goes above a narrow high window and off
    again below that same window. I also want it to shut down the pump if
    it goes below a bottom window and able to come back on above that
    lower window when it hasn't rained for the preset number of days.
    Upper and lower windows could be detected with 2 op amps for the
    upper and 2 for the lower. I've done something similar to this before
    but was a number of years ago and I can't find the documentation as to
    what I did and parts I used. They probably don't make those parts
    anymore anyway.

    The newest data book I have is a TI linear volume 3 from 1992. Do
    they have hard copy data books any more or they all on CD?
     
  2. John Barrett

    John Barrett Guest

    PIC or Atmel -- I recommend the Atmel because of the readily available free
    C development tools and a reasonably inexpensive development kit that
    handles most of their chips. ($250 or so for the dev kit, or you can find
    programmers for less than $50 and go right to circuit) I dont know about PIC
    dev kits but I'm sure they are out there, as are cheap programmers :)

    So its really more a question of what languages do you know, and what dev
    tools are out there for those languages, rather than what chip is best....
    even the smallest 8 pin PIC will handle the application you described with
    I/O to spare (maybe use the left over pins for some status LEDs or a serial
    interface back to your PC for monitoring and remote control)
     
  3. A small PLC would probably be simpler, but I don't think you are looking
    for dimpler. I'd look for an eval board to start with. Almost any
    small micro. AVR, MSP, ARM just about any would fit the bill.
    Data books have become rare, although still nice to have. CDs, are
    thankfully, even rarer.

    Robert
     
  4. I've seen systems that measured the moisture level in the soil and ran the
    pumps accordingly. Popular in Australia I believe.



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  5. Guest


    What kind of sensor do they use? I might want to use that as
    another condition to be examined by the micro controller I really
    don't want to buy a pre-manufactured system, I want to design and
    build one for educational and potential job related experience.
     
  6. Guest

    I guess that I need to go to their web sites to find out their
    specifications and if I think they would be a good learning tool.
    What is a popular one that would have the most relevance to many
    designs?

    Do some companies still publish data books? How does one go
    browsing for parts these days?
     
  7. Guest

    I don't know, but a google search on "soil moisture sensors" threw up
    a bunch of interesting sites. Here are two of them.

    http://www.delta-t.co.uk/groups.html?group2005092332137&gclid=CLKQ0Nyo_ooCFSYbEAodPBRZFg

    which looks as if they rely on measuring conductivity - almost
    certainly with an AC-excited bridge.

    http://www.cropinfo.net/AnnualReports/2001/Popsensortest01.htm

    which compares six different sensors - I didn't get much insight out
    of it, but I didn't read it carefully.
     
  8. Fred Bloggs

    Fred Bloggs Guest

    The first order of business in a project like this is to FULLY
    understand the PROCESS you are trying to control. In your case this
    means you must find out more about agricultural irrigation and the
    various considerations that go into controlling its application from an
    agricultural perspective. You don't just jump in with a bunch of minutia
    about some "manifolded" buckets, pressure sensors, sprinklers, and other
    odds and ends that you can kluge together to realize your hazy and
    unsatisfactory idea of what should be good enough. I will give a hint
    and tell you right now that there is no such thing as an irrigation
    controller that works based on a "preset" number of days since last
    rainfall- that strategy is absurd to the point of warranting severe
    condemnation. You need to know 1) how much did it rain, 2) weather
    conditions following so as to stress the transpiration rate of the
    crops, 3) the soil moisture requirements of said crops relative to the
    integration of the estimated transpiration rate as a function of stage
    into plant growth development cycle, 4) most favorable time of day and
    location to apply water, sprinkling is one of the most inefficient means
    BTW, 5) soil type insofar as water absorption and retention rates,
    6)...and host of other parameters related to *agriculture*. It is only
    *after* you have developed a *thorough* understanding of these
    requirements and a *thorough* understanding of the various doctrinal
    control methodology that have proved successful in practice can you even
    begin to *think* about an instantiation using your little collection of
    buckets, pressure sensors, and what-nots. Get it?
     
  9. That depends on the kind of designs you are looking at. Personally I've
    defaulted to ARM variants as my starting point, they are readily
    available with a lot of variety and reasonable inexpensive in small
    quantities. They are also big enough in terms of available memory and
    processing power to takle quite a range of problems. foe specific jobs
    other processors may be a better choice to get some desired chara
    cteristic or peripheral (physical size, high res A/D, low cost, some
    specific obscure I/O etc...) I don't much like PICs but that's a
    personal quirk, some swear by them, some at them.
    There are a few. Deutsch come to mind as one whose data book is much
    better than their web site, in their case mainly because of very poor
    PDFs. Most of the data books I get now seem to be from connector
    companies. For semiconductors you generally need to beg reps to get
    Data books, Sometimes they are available, often they are not. The last
    I got on a micro was a few years ago for a 80C196 variant, the rep had a
    couple printed out for me.

    Browsing for parts is a matter of browsing web sites of the
    manufacturers and, especially if you are using small quantities,
    checking a few on-line distributers for stock.

    Robert
     
  10. Most manufacturers have all their datasheets, selection guides, and
    app notes available on-line. Searching a distributor's website, such
    as Digikey or Mouser, can give you a good idea of what parts are
    actually available.

    A google search for IC part number +datasheet will generally locate a
    datasheet (although you will often get several pay datasheet sites
    listed before the manufacturer's site)


    --
    Peter Bennett, VE7CEI
    peterbb4 (at) interchange.ubc.ca
    new newsgroup users info : http://vancouver-webpages.com/nnq
    GPS and NMEA info: http://vancouver-webpages.com/peter
    Vancouver Power Squadron: http://vancouver.powersquadron.ca
     
  11. Guest


    What I get is that you don't thoroughly understand that the more
    important consideration at this time is to learn how to utilize a
    micro controller and build a system that functions as intended. Your
    other considerations are of merit but this is for a single residential
    application, as in my house, not some large scale farming operation.
    It is a lot more practical than some of these other micro
    controller projects I have seen posted here by some under-graduate
    college students that are assigned their by their instructor or
    professor to build some circuit that counts the revolutions of some
    shaft or whatnot over a given amount of time. Maybe I'll want to
    incorporate those other aspects you mentioned above at a later date
    but for now I just want to controllably water the lawn and learn how
    to use and program a micro controller.
     
  12. Just a couple of probes in the ground. Stainless would be best I assume.
     
  13. ehsjr

    ehsjr Guest


    "Program" it first at the functional level, before choosing
    the ucontroller. Two conditions do not "go through" the
    ucontroller: When the low window bottom sensor is dry,
    the pump is off regardless of any other conditions; when the
    high window high sensor is wet, the pump is on regardless
    of any other conditions. That said, you still might want
    to have the uc look at them for errors, like the low window
    low sensor dry but the othere window sensors wet. Once you have
    laid out all the functions you want you should be in a better
    position to pick the uc. But it really doesn't matter, as
    you indicated that you haven't worked with them.

    So, what you really want is someone to provide a complete
    solution, with the uc already chosen and the code written,
    or someone with experience to tell you which uc to use so
    that you can then learn how to use that particular uc
    family. That experienced person will be better able to
    meet your needs after you have spelled them out. For example,
    you did not address resetting the timer, error checking
    the sensors, what to do if the pump is running and it starts
    raining, whether the timer needs to run during a power failure,
    what the power on reset state should be and who knows what else.

    I'm having a hard time figuring out how this project
    demonstrates the need for a uc, but I think you could
    demonstrate the parts cost advantage of one.

    I'll show a hardware solution below. The purpose is
    really background to show that the person reading the
    resume may think "why in the hell is he showing such
    a simple use of a uc, when so much more could be done?"

    Excluding the timer, a simple hardware solution is a couple
    of relays. I'll draw the comparator outputs as switches (saves
    drawing the op amps) All switches made when wet.

    Your rain sensor (RS - on when wet) :

    /
    + ---o o---+---> timer start on break (-)
    RS |
    [R]
    |
    Gnd --------+

    Your low window level top of window (TW) and bottom of
    window (BW) sensors (on when wet):

    /
    +---o o---o--- < Low Relay 1 point
    | BW ^---+
    | |
    | / |
    + ---+---o o----------+
    TW |
    [Low Relay]
    |
    Gnd -------------------+

    When the tank is filling, BW closes first as the
    level rises. When the water reaches the top
    of the window, TW closes and the relay energizes.
    It stays energized, if the water level drops, until
    BW opens.


    Your high window level top of window (TW) and bottom
    of window (BW) sensors (on when wet):


    /
    +---o o---o--- < High Relay 1 point
    | BW ^---+
    | |
    | / |
    + ---+---o o----------+-------< from timer output
    TW |
    [High Relay]
    |
    Gnd -------------------+

    Operates the same as the bottom window sensors.
    In addition, the relay can be controlled via the
    timer. That meets your condition of the pump
    operating when the timer calls for it, regardless
    of the status of the upper window sensors.

    AC ----- < Low Relay 2 Point
    ^------+
    |
    +--- High Relay 2 Point
    +--^
    |
    [Pump]
    |
    AC -----------+


    The point of all that is to show that the uc
    is not providing a whole bunch of function that
    mandates its use over hardware. You want the
    resume to sell a product - you - to the company.

    Maybe it would be sufficient for your project to use
    the uc as the basis for your timer - I don't know. It
    seems to me a waste of uc power to use it only as a
    timer in this. Neither the hardware nor software solution
    can be given until timer reset is defined, but the
    hardware solution might be a counter like a CD4060
    and support components or maybe cascaded ICM7242's.
    I think it would be a better project if you could do
    all the "thinking" with a uc - and show enough need
    for "thinking" that the person reading the resume
    is impressed. As stated, your project doesn't do that,
    in my opinion.

    Suggested additions: add zones, with individually
    selectable on times like 4 hours every other day
    or so many minutes daily or once a week or whatever,
    sensor logical error checking, maybe an "it's been
    too dry for too long" alarm to a human operator, etc.
    The more practical flexibility you put into it, the
    better.

    Ed
     
  14. John Fields

    John Fields Guest

    Iridium.
     
  15. Guest

    Platinum is usually preferred for conductivity sensors, but soil
    conductivity is pretty low, so stainless steel would probably be good
    enough - the layer of chromium oxide (or whatever) that stops
    stainless steel from rusting has a rather unpredictable range of
    thicknesses and resistance, but the additional resistance of the oxide
    layer is usually negligibly small when you are measuring soil
    conductivity.
     
  16. That depends on the kind of designs you are looking at. Personally I've
    defaulted to ARM variants as my starting point, they are readily
    available with a lot of variety and reasonable inexpensive in small
    quantities. They are also big enough in terms of available memory and
    processing power to takle quite a range of problems. foe specific jobs
    other processors may be a better choice to get some desired chara
    cteristic or peripheral (physical size, high res A/D, low cost, some
    specific obscure I/O etc...) I don't much like PICs but that's a
    personal quirk, some swear by them, some at them.
    There are a few. Deutsch come to mind as one whose data book is much
    better than their web site, in their case mainly because of very poor
    PDFs. Most of the data books I get now seem to be from connector
    companies. For semiconductors you generally need to beg reps to get
    Data books, Sometimes they are available, often they are not. The last
    I got on a micro was a few years ago for a 80C196 variant, the rep had a
    couple printed out for me.

    Browsing for parts is a matter of browsing web sites of the
    manufacturers and, especially if you are using small quantities,
    checking a few on-line distributers for stock.

    Robert
     
  17. Fred Bloggs

    Fred Bloggs Guest

    Maybe for a self-centered narcissist it is more important, but, in the
    real world, the individual engineer/technician is subordinate to the
    goal of product creation to the point of being a completely
    insignificant non-entity of the lowest order. Don't plan on impressing
    anyone with your resume.
     
  18. mpm

    mpm Guest

    Personally, you can cobble up a one-off sprinkler doo-hickey and I'm
    sure it'd be real nice.
    But you can perhaps accomplish the same thing by using a Programmable
    Logic Controller.

    Go to AutomationDirect.com and take a look at the DL5 and DL6 models.
    (There are plenty of others to choose from).

    This will get you some good, rock-solid hardware to play with.
    Lots of options, etc... Inputs/outputs comms, .. (and probably for
    less $$ than you would otherwise spend in development)

    As for the resume, well, these things are usually programmed in
    "Ladder-Logic".
    And these days, that's a weird-enough term to catch someone's
    attention.
    If they're actually paying attention that is.

    I'm afraid have to agree with Fred's comments (above) that the days
    of impressing anyone with your engineering resume are not what they
    used to be...

    -mpm
     
  19. Guest


    I certainly don't expect to impress you with much of anything. I
    would guess that a bunch of college students, year after year,
    devising the same circuit that counts the revolutions of a shaft to be
    of greater import and practical than someone showing a little
    imagination and building something different.
     
  20. Guest

    Have you used the Keil kits and are their eval boards
    interchangeable between kits? If I get one starter kit with a certain
    chip eval board, can I just get another eval board for another chip
    and it work?

    My favorites are DigiKey and Mouser.
     
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