Gadgeteer plant monitor wants it wet and photogenic


[Christian] is growing a tomato plant on his desk and wanted to capture some time-lapse images of its progress. To that end he built a rig that monitors moisture levels and snaps images at regular intervals.

The hardware he’s using is part of the Gadgeteer family. These run a .NET micro framework and are modular which makes for easy assembly. A laser-cut plywood stand helps to position the camera module for the best shots. Its takes a picture of the seedling once every ten minutes. There is a quartet of RGB LEDs surrounding the lens. They help illuminate the subject for each picture. But [Christian] also mentions that the red LEDs provide light the plant needs to grow (we raise an eyebrow at that claim, but in truth we have no idea if red LEDs make plants grow or not). There is also a moisture sensor which you can see inserted in the soil.

The images and moisture readings are all pushed to a server. There is an Ethernet board near the base of the rig. It uses POST to send the image, which is saved by a server-side script. The moisture data is sent via a GET command.


  1. ummdorian says:

    Where is the time-lapse video, man?

  2. Joejoedancer says:

    Seems you could do this with a raspberry pi for much cheaper and less coding (python). Love plants and electronics though. Have been developing a greenhouse controller myself so good luck. And yes LED’s can contribute to plant growth.

    • gabriel says:

      it’s a board that you code in C#. nobody is looking for costs or simplicty with that.

      it’s liking looking for opennes in a platform where all the coding is done in java…

  3. Very cool! Keep the Gadgeteer projects coming!

  4. Ren says:

    Green LEDs don’t work very well for plants (chlorophyl reflects green light instead of absorbing it).

    • anon says:

      Can somebody smarter than me run down the math to see if a typical 1W red LED can actually help a plant in a significant way?

      I know the principle is true, but somehow I doubt a puny LED can do anything significant. Professional greenhouses use kilowatts of arc light, not a couple watts. Granted over a wider area, but still.

      • Hugh says:

        Sunlight is typically 300 watts/meter^2 and so provided that the LED is focused, the LED would be supplying light energy to around 50cm^2. (300*50)/10000=1.5 watts (the sun typically produces 1.5 watts per 50cm^2). Provided that the LED is 100% efficient, then the LED would actually supply more energy due to day and night cycles.

      • soopergooman says:

        Red or Blue LED’s are the best for growing, it is what NASA uses on the ISS to grow plants and also the two together will give great yields and also helps with healing of cuts and minor scrapes.

      • soopergooman says:
      • jaded says:

        At full power drawing 300mW, an RGB5050 chip can emit a max of 1000 mcd. (The gadgeteer board draws only 20ma at 3.3V or 66mW max, so it’s obviously not producing maximum light output.) Even assuming a miraculous conversion efficiency, at the approximately 10cm distance and mostly wasted beam angle of 120 degrees, 1mcd is still only delivering about 100 lux to the leaves, or pretty much “close to dark” as far as plants are concerned. So no, even four of them won’t provide enough energy to help growth much. I suspect the light his plant is using is coming from his office lighting and windows.

        He could really make a difference by placing a reflector around the LEDs to focus the light on the plant. He could also lower the arm to within 1cm of the leaves. But that would kind of spoil the photography aspect of the project.

        A good experiment for him would be to grow a tomato plant for a set period of time with the LEDs on full power, then measure it. Repeat the experiment with a new plant and leaving the lights on only long enough to take the photos, then measure again.

        Oh, and plants need both red and blue light in their spectrum. Blue light promotes leaf growth, while adding red light promotes flowering. But just pure red plus blue LEDs produces some stunted plants.

        • Tom says:

          Not to moot your point, but the current draw of the main board doesn’t dictate the current draw of the LED. I play with a Gadgeteer kit at work, and there is no way that the entire setup draws <= 20mA of current when working with the LCD panel, and multiple LED modules!

          I'd also be curious to know just what sort of percentage difference the LED's are having on the plant growth though…

  5. Tim says:

    I have successfully grown plants under LEDs, though it should be using blue and red LEDs, since chlorophyll A and B absorb these two areas of the spectrum best…

  6. emnov says:

    “want it wet and photogenic” – that’s what I said ;-)

  7. Raisin says:

    What is the best method for sensing moisture? Resistive? Capacitive?

    • Joejoedancer says:

      Resistive is the easiest but leads break down. Capacitive is better but harder to execute properly.

    • rj says:

      They’re all awful. Both have problems with significant drift of the sensor over time, nevermind any effects with corrosion of your sensors.

      The last time I asked someone, they told me that there was a commercial vendor that used capacitive sensing at 10 megahertz, which is ludicrously high in comparison to any other I’ve heard.

  8. rj says:
  9. bmq215 says:

    Chlorophyll appears to absorb 430-460nm and 640-600nm most strongly. LED grow lights with this combination (usually about 1:2 blue to red, IIRC) work very well.

    Anyone interested in digging deeper into the effects and construction of such lights should check out some of the more “illicit” gardening forums. The members aren’t the most eloquent, but I’d wager that some of the greatest horticultural minds of my generation can be found there.

  10. W K says:

    LED’s have just started making their way into the research field around 5 – 7 years ago and it has helped that pricing has gone down and power-efficiency has gone way up. I was part of a project that was building a full sunlight system and estimated we needed roughly 8kW to hit that mark on 20 sqft, but we were able to hit that mark using only 3.1kWs.

    Red lighting systems have been fairly common in the research space for quite some time. Blue is absorbed by plants, however it is red-shifted (energy released moving the photon from a higher energy state to a lower energy stat) before it can be absorbed by either PSII or PSI (680nm and 700nm, respectively), the photosynthetic reaction centers.

    Blue light is important as there are several bio-synthesis pathways that are light catalyzed and require the blue spectrum of light, however you only need a little bit of the blue. Most commercial growth chambers use ‘warm’ light colors (ie heavy in the reds/yellows) for best results. Also, plants typically need a far-red (infrared) to signal night (most chambers do this by just turning off incandescent lamps during the night period.

    The hack looks pretty cool, you would be surprised at how much interest there is in industry into systems that do stuff like this, but a bit larger scale!

  11. DivePeak says:

    You need blue light for growth, then red or orange light to trigger budding & flowering.

  12. Ideally you want a wide spectrum of red and blue lights, verging on infrared and a good blue on the other end of the spectrum. LED grow lights have both and emit quite a bit of warmth.

  13. sarinkhan says:

    What about ultraviolet?
    Is it important for plant growth?
    When i have time i will try to have a plant enclosed in a transparent box (to keep
    water for evaporating, thus keeping constant moisture level),
    with various LED colors.
    This is also interesting for aquariums; i have read quite a lot of stuff about aquarium lights, but i guess that it may be slightly different for underwater plants.

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