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  1. #1
    Join Date
    Dec 2006
    Location
    San Jose, CA, USA
    Posts
    898

    Default Cheap cloud sensor - any interest?

    I've been using a fairly cheap homemade IR based cloud sensor for the last few months and it seems to be working pretty well.

    I've just upgraded to a new IR thermometer which measures the sky temp down to -40C, increasing the usefulness in low ambient temps over my old sensor which only measured the sky temp down to 0C.

    The new sensor costs about $145 at retail, which is a fair bit cheaper than the current Boltwood sensor ($1500), although it doesn't measure windspeed nor does it have a rain sensor. It does measure relative humidity, which may possibly be used as an indicator of rain though?

    The way I figure things, if there are no clouds, there's unlikely to be any rain, so this is better than nothing...

    Anyway, I've written some monitoring software which takes the readings from the sensor and graphs the cloud conditions - my live sky status page is viewable here:

    http://winfij.homeip.net/CloudStatus.html

    I'm considering integrating this into an ACP weather server app which will then be able to initiate an ACP shutdown when the clouds roll in - is there any interest from anyone in having this capability available from a DIY solution?

    I bought my IR thermometer from here:

    http://www.kvmtools.com/servlet/the-...C-RH401/Detail

    It's got an RS232 output, which you just need to hook up to a PC and run my data gathering software. It takes a 9v DC power input (not supplied).
    You'd need to build a sun/rain-proof container for it - I used a modified plastic snaplock food container, with a sensor window covered with kitchen clingfilm (seems to be transparent to IR).

    So, any interest in me extending my graphing software into an ACP weather server, to give a low cost DIY cloud sensor solution for automated observing?

    Cheers,

    John

  2. #2

    Default

    I too have been interested in this sensor as an inexpensive alternative. Am planning on adding this sensor to the Boltwoods that I now support. Since the actual IR sensor is about $100, this is quite a nice buy. I plan to do A/B calibration comparisons with Boltwood. I'm also working on an inexpensive rain sensor so that this unit could actually be under the dome shutter, which only would open when there was no rain present. Does that sound interesting?

  3. #3
    Join Date
    Dec 2006
    Location
    San Jose, CA, USA
    Posts
    898

    Default

    Hi Stan,

    I did think about constructing a sensor from discrete components (my previous sensor was more along those lines) but I felt that an off-the-shelf thermometer would be more readily available to those interested.
    However, it's unlikely it will be possible to do the same with a rain sensor - those shipped with weather stations are designed for measuring bulk flow rates rather than detecting the first few drops.
    Are you planning on building and selling the rain sensors (and IR sensors), or just providing build schematics?

    If you're planning on adding support for this thermometer serial output to your weather server, that'd be great - saves me the trouble

    These things are a double-edged sword though - it's sometimes a little depressing to see the graphical history of just how few clear nights you really get...

    Cheers,

    John

  4. #4

    Default

    Actually I am committed to building an inexpensive rain detector for sale. The circuit is quite simple and I'd also include it for the DIY folks. I agree that the best indicator of sky safety is sky/cloud temperature. My site in MD clouds up fast. Remotely in NJ, I watch live weather radar from Baltimore and as the cloud cover sweeps East over the Chesapeake, my sky temperature (Boltwood I now) continues to warm in advance of the weather front. A cheap rain sensor with this sky temperature sensor under cover until the dome shutter opens could work out fine.

    I should have support for this device rather soon.

    Stan

  5. #5
    Join Date
    Dec 2006
    Location
    La Palma, Canary Islands
    Posts
    29

    Default

    I was looking a building a cloud sensor using an off the shelf IR Thermometer which I brought for 29GBP. I did some testing back int he UK and it meausres about -40 with clear skies and nearer 0 with clouds.
    Theresa Davis
    La Palma, Canary Islands
    http://casa-estrellas.blogspot.com/

  6. #6
    Join Date
    Dec 2006
    Location
    San Jose, CA, USA
    Posts
    898

    Default

    Interesting - do you have a link for that thermometer, or a part/model name?

    I couldn't find one for that price which had a PC output built in, thus using one which cost about 75GBP (at the current exorbitant exchange rate!)

    John

  7. #7
    Join Date
    Dec 2006
    Location
    La Palma, Canary Islands
    Posts
    29

    Default

    It didnīt have an RS232 built in. I was going to tacke it appart and just use the sensor and circuitry. kind of like the toucam mod idea.
    Theresa Davis
    La Palma, Canary Islands
    http://casa-estrellas.blogspot.com/

  8. #8
    Join Date
    Dec 2006
    Location
    San Jose, CA, USA
    Posts
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    Default

    OK, gotcha.

    Well, for a few bucks more, you can get one you can use out of the box with no mods necessary

    Bear in mind that for cloud detection, you'll need the ambient temp as well, since it's normally done by monitoring the delta between the ambient and sky temps.

    John

  9. #9
    Join Date
    Oct 2005
    Location
    Strongsville, OH
    Posts
    1,548

    Default

    Hi John,

    To your original question, my answer is "yes," I think.

    Since my "dome" is nothing more than a bag which I manually take off/put on, all I'd be looking for is an "alert" to tell me to wake up and cover the scope before it starts raining! I'm not quite sure how that would work - e.g. having the PC out by the scope start making noise wouldn't help. I'd need it to call me on the phone or something like that...

    Jim

  10. #10

    Default

    Jim- You may want to consider the so-called "lower cost" Boltwood. It's a standalone at $349 and aparently has an audible alarm when sky is deterioating. Look at cyanogen.com

    Stan

 

 

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