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    RasWIK as a basic Weather Station?

    For discussion of DIY weather equipment - sensors, accessories, improvements to existing kit etc
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    logjam
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    RasWIK as a basic Weather Station?

    Post by logjam » Mon 17 Feb 2014 6:03 pm

    I've been recently experimenting with Ciseco's 'RasWIK'. It has a tiny radio tx/rx which fits the Raspberry PI, and then all the connections are made to another board in radio contact with it.

    I've been able to measure temperature and light intensity as well as wind speed using relatively simple python routines. In addition I've now successfully logged these (separately) to a file over several hours in a form not dissimilar to the ones generate by Cumulus. (Only one piece of information at a time at the moment.)

    I am planning to see if I can put all this together out in the Stephenson Screen logging multiple data.

    Before I start has anyone any comments on this unit and its suitability?

    http://shop.ciseco.co.uk/raswik/

    AllyCat
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    Re: RasWIK as a basic Weather Station?

    Post by AllyCat » Mon 17 Feb 2014 8:36 pm

    Hi,
    logjam wrote:I've been able to measure temperature and light intensity as well as wind speed
    Sorry, I'm trying not to be too "negative", but I have to ask "with what accuracy and for how long?". Also how did you measure the windspeed? Thermistors and LDRs may be OK for low-cost commercial products but "Homebuilt" stations normally use precision, pre-calibrated sensors employing one of the standard digital data buses, such as "One Wire", SPI or I2C. Thermistors and LDRs are also the rather "easy" sensors, but any self-respecting station needs humidity, atmospheric pressure, rainfall and wind direction, etc..

    Also, for any system which is "wireless", it's necessary to consider where it is to get its electrical power from? The design of a transmitter system to run 24/7 with good reliability is not trivial. However, I'm not clear exactly what RasWIK really is, or even what radio technology it uses. The links seem to lead to virtually all the "buzzword" hobby products such as RasPI, Arduino, Zigbee, PICaxe, etc..

    It depends what you ultimately want to achieve (and does it need to be wireless). But if it is to use Cumulus then you should perhaps work "backwards" from the Cumulus interface (or hope that Steve to releases his Linux version) rather than forwards from a few arbitrary (and probably not very accurate) sensors.

    Cheers, Alan.

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    logjam
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    RasWIK as a basic Weather Station?

    Post by logjam » Mon 17 Feb 2014 11:07 pm

    Not at all, I welcome any observations, although I'm only experimenting at this stage, and I haven't even thought about measuring other things. I assume that if the system works then it is a matter of adding sensors as I go along. It is the fun of doing it that matters mostly to me.

    The units are specifically the XinoRF
    http://shop.ciseco.co.uk/xinorf-100-ard ... ansciever/

    and the 'slice of radio'
    http://shop.ciseco.co.uk/slice-of-radio ... pberry-pi/

    The wind speed was obtained by counting the number of switch closes in a fixed time. I've not attempted to calibrate it at this point. (The experiment was being done inside after all) A rainfall counter would work in the same way. Wind direction is slightly more complicated, but I believe it is about applying mathematics to a resistance value. There are other ways of doing it of course. I haven't a clue about humidity and pressure, but obviously there must be sensors which deal with that as well.

    Obviously the system is only as good as its sensors, but at this stage I was interested in the general principle, and in particular the attributes of the input board.
    I take your point about powering it while having it outside.

    I wasn't thinking of using Cumulus, although when writing the software it would be a good standard to aim for.

    AllyCat
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    Re: RasWIK as a basic Weather Station?

    Post by AllyCat » Tue 18 Feb 2014 12:07 am

    Hi,

    Yes, it's potentially an ideal educational project. But it will very probably cost significantly more than a low-cost system like Maplin's, so it's worth trying to make something "better" (more accurate or reliable). There's quite a lot of scope to improve (or improve on) the Fine Offset (Maplin) sensors.

    My suggestion is to look at the PICAXE system, which is fairly easy to program, has the ability to read some of the more "exotic" sensor types. It can also drive a wireless transmitter and can (be arranged to) work on battery power for a very long period of time.

    Cheers, Alan.

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    logjam
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    RasWIK as a basic Weather Station?

    Post by logjam » Tue 18 Feb 2014 9:30 am

    My rationale behind the idea is that my present 'Maplin' set up is basically sensors connected to a console which is connected to a laptop via the Cumulus software. As a workable system it fails mostly because of the console and it takes up the resources of an expensive (to buy and run) laptop . It occurred to me that it would be far better to connect the sensors directly to a programmable computer and by-pass the console altogether.
    The Pi itself is cheap and versatile, and the breakout boards even more so. I certainly don't mind buying the boards and experimenting. My main problem is that I'm not au fait with computer hardware. (Software, yes.) I have bought the piface board, but it only has digital inputs. (I'll use it for something else) The Ciseco boards have analogue inputs which make them more suitable for a weather station. The radio system is 'on-board'.

    So what exactly are these exotic sensors, and in real terms how much better are they?
    How would a break out board be powered when located somewhere in the garden?

    AllyCat
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    Re: RasWIK as a basic Weather Station?

    Post by AllyCat » Tue 18 Feb 2014 11:02 am

    Hi,

    One approach is to add a radio receiver to the Pi and receive the data from an existing "Maplin" transmitter, for ecample as described in Kevin's documentation linked from this recent thread. That overcomes the "issues" associated with powering remote wireless sensors and perhaps with low-cost wireless receivers.

    Concering the sensors, they are very often NOT analogue (output) devices, or require a very accurate analogue-digital converter. An example is the DS18B20 and again here is a recent relevant thread (which includes some contributions from others than me ;) ). You may find other interesting threads in the Homebuilt section, perhaps even going right back to the beginnings of the blake-larson sunshine recorder.

    In the very brief look I took of one of the RasWIK projects, my "concern" was the "accuracy" quoted as "about 10% between 0 and 40 degrees C". Not only is that "poor" (for weather logging purposes) but it's not the correct way to specify a temperature sensor's accuracy. Does it imply that it's perfectly accurate at zero degrees C in the UK, but not at 32 degrees F in the USA? :? Temperature accuracy should always be quoted in the form of "+/- degrees" (with perhaps a further "offset" qualification).

    Cheers, Alan.

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    logjam
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    RasWIK as a basic Weather Station?

    Post by logjam » Tue 18 Feb 2014 2:34 pm

    Thank you for the links. I'll study those in detail later today.
    It raises issues about accuracy of the devices, and compensating for the known characteristics of the sensor.

    Regarding the 'inventor's kit', and the other projects, they are there only to demonstrate the board's ability. I wasn't thinking I would use any of the included components or necessarily even the software routines they use, but they would be a good place to start and practice with it.

    It would be good to hear from anyone here who has experience of making their own station, even in part.

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    mmcp42
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    Re: RasWIK as a basic Weather Station?

    Post by mmcp42 » Thu 20 Feb 2014 9:29 pm

    I'm using exactly that combination in my home-brew weather station right now
    XRF in an Arduino board, and another on a slice of pi

    works a treat

    I have also successfully used a SIM900 to send data over FTp

    I'm looking to replace the radio with an RN-XU unit for direct connection to Wi-Fi
    weather station here: http://www.mmcpix.com/wx.html

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    logjam
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    RasWIK as a basic Weather Station?

    Post by logjam » Thu 20 Feb 2014 10:17 pm

    I would be interested to know how you power the Arduino board.
    What kind of range do you get with this system? Do you use an external antenna, or is the board alone enough?

    As soon as I get some time, I'm going to set up a test using some spare kit. I think a rain gauge will be a good start, along with the photo-resistor.

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    mmcp42
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    Re: RasWIK as a basic Weather Station?

    Post by mmcp42 » Thu 20 Feb 2014 11:13 pm

    logjam wrote:I would be interested to know how you power the Arduino board.
    What kind of range do you get with this system? Do you use an external antenna, or is the board alone enough?

    As soon as I get some time, I'm going to set up a test using some spare kit. I think a rain gauge will be a good start, along with the photo-resistor.
    Single 1000 mAh 3.7volt LiPo cell charged by a solar panel
    Range about 50', but a lot more is claimed to be possible
    Just using the 3" tail the boards came with



    edit to change the LiPo to 1000 mAh
    weather station here: http://www.mmcpix.com/wx.html

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