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Rain Detector

Discussion in 'Embedded' started by scilent-project, May 26, 2006.

  1. Hi
    For final year project,I want to design a rain measurement device which
    can be read through parelle port of a PC.
    All ideas on this topic are cordially welcome.

    thanks in advance.
    scilent-project, May 26, 2006
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  2. scilent-project

    Peter Guest

    Pulsed microwave radar between 1 and 10cm is quite good for detecting rain
    as it falls.

    Peter, May 26, 2006
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  3. Please define more precisely what do you mean by "rain measurement".
    Do you want just to (a) detect it is raining or (b) measure the amount
    of precipitation?
    There are many simple solutions for (a), a simple switch activated by
    the weight of water collected in a small vessel, detecting the change
    in conductivity of "something getting wet", etc.
    (b) will require collecting rain water and measuring it somehow.
    Weight, height of water in a container of known dimension, pressure
    generated by the collected water, changes in light transmission
    through the water, etc.

    You should focus first on the physics of the problem. Once you know
    what to measure and how to measure it, the interface to the parallel
    port will probably be the least important part of the project.
    Roberto Waltman, May 26, 2006
  4. scilent-project

    Tom Lucas Guest

    1) PC sends constant stream of data from Parallel port
    2) PC is left out side.
    3) Rain kills PC
    4) Stream of data stops. Rain detected.

    Seriously though, I'd be inclined to use the serial port because it is
    simpler and needs fewer wires. Use USB and get power thrown in for free!
    However, the PC end is the least of your troubles (but don't leave writing
    the driver until the day before the project is due because it can take a

    As for the detection, the water level detection in the Industrial Boiler
    Control I'm working on uses capacitance probes and is pretty sensitive. They
    work by using an oscillator whose frequency varies with the capacitance of a
    probe dipped in the water. Measure the frequency - know the depth. The
    concept will probably work with a large flat probe to be spattered by rain
    instead of a long thin dipper. Or you could have a bucket with a dipper in

    Of course I have seen simple rain detectors which are just two wires beside
    each other. When a drip bridges the two then the circuit is completed.
    Tom Lucas, May 26, 2006
  5. scilent-project

    Oscar Guest

    Look at web sites for commercial irrigation systems. Most of them have a
    rain detector nowdays to prevent watering when its raining or has rained
    recently. Get some ideas from them and then design a better one.
    Conductivity through collected water and periodic cup dumping are common.
    Oscar, May 26, 2006
  6. (b-1) Measure the total rainfall over a period of time (e.g.
    total inches the past 24 hours).

    (b-2) Measure the instantaneous rate of rainfall (inches/hour).
    Grant Edwards, May 26, 2006
  7. In a cold climate, you should define how to handle snow and sleet and
    how to prevent the collected water from freezing at night.

    In a hot climate you have to consider about evaporation especially if
    the air becomes dry and windy after a shower.

    Paul Keinanen, May 26, 2006
  8. scilent-project

    Leon Guest

    An interesting technique is to count the impacts from raindrops in a
    given area, using a suitable transducer. It can be quite accurate,

    Leon, May 27, 2006
  9. Do also have to measure the impacts to get an estimate of drop
    Grant Edwards, May 27, 2006
  10. scilent-project

    Leon Guest

    I can't remember. It might be accurate enough if an average size could
    be calculated.

    Leon, May 27, 2006
  11. You would have to apply the Marshall-Palmer-law and the
    Laws-Parsons-distribution to get a better relation between how much is
    raining and the drop size distribution.

    Paul Keinanen, May 27, 2006
  12. The 10 cm (3 GHz) wavelength might be usable for detecting huge hails,
    but even a heavy (150 mm/h) rain will attenuate the 3 GHz signal with
    only 0.1 dB/km, so I very much doubt that you would get any usable
    reflections from the raindrops.

    Frequencies between 10 GHz (3 cm) and 100 GHz (3 mm) would be more
    suitable, although it might be hard to separate between drizzle and
    fog at the higher frequencies.

    Paul Keinanen, May 27, 2006
  13. scilent-project

    Steve Guest

    Picking up on this point - I'm interested in making an accurate
    aquarium level detector at the moment (saltwater) , and wonder how
    good this method could be. In an ideal world something like 1 mm
    resolution would be good. Could this method achieve this. Any
    suggestions on the general type of oscillator and ballpark frequency
    that might work best?

    Steve, May 28, 2006
  14. scilent-project

    John B Guest

    scilent-project scrobe on the papyrus:
    No, it seems from your post that you want the good folk here to design
    it for you, so that you can take the credit. Go away and design
    something, then come back here when it doesn't work.
    John B, May 29, 2006
  15. scilent-project

    John B Guest

    Oscar scrobe on the papyrus:

    Ah, the Chinese water clock.
    John B, May 29, 2006
  16. scilent-project

    Hul Tytus Guest

    Steve - what's the depth of the tank? ie 1mm in what total?

    For a possible start, a double sided pc board cut to 10mm by ?mm (radio shack?)
    with a capacitor, inductor & transistor soldered on and some paint should
    give you first info.

    Keep in mind that the dielectric constant of water is around 70 & epoxy
    board material is about 4 (check both).

    Hul Tytus, May 29, 2006
  17. scilent-project

    purple_stars Guest

    biological control unit, definitely.

    use a pic with usart, program that and hook it up to the pc serial port
    via a long serial cable that goes outside on the front porch. use
    level converts so you get a good distance on the cable. attach the pic
    to a switch. when the switch is activated that sends a signal to the
    pc that does whatever you want it to do. set a big glass of tea on the
    porch to attract control unit (i.e. your mom) out on the porch. when
    she sees rain she pushes the button.

    alternatively, for more fidelity, you could have a pot and use a/d
    conversion to get a range of values. label the pot something like
    "ain't raining", "ain't much rain", "little bit a drizzle", "it's
    rain'n perty good", "raining a lot", "cats and dogs", and "i think i
    just saw toto". then instruct control unit about the finer points of
    polling vs. interupt driven i/o and instruct control unit to
    periodically poll (i.e. look) and see how much rain there is and to use
    the pot to select the proper value.
    purple_stars, May 29, 2006
  18. scilent-project

    Steve Guest

    Thanks, it's a pretty shallow tank, about 30cm. I'd need to make a
    non-copper electrode design for this as there are inverts in there. I
    was thinking about a stainless probe or pair of to do the sensing.

    Steve, May 29, 2006
  19. scilent-project

    Hul Tytus Guest

    Steve - what are inverts?


    Hul Tytus, May 29, 2006
  20. scilent-project

    Steve Guest

    Ah, a bit OT I guess, but invertebrates, as in non-vertebrate
    organisms, include corals and other non-fish marine things - hence
    the need for precise level (== water specific gravity) control to keep
    them. Copper in greater than trace concentrations is highly toxic to
    marine invertebrates, hence you need to avoid same in any electronics
    in contact with aquarium saltwater.

    Steve, May 30, 2006
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