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The Little Green Tower

A mist-based tower system for growing leafy green vegetables

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The Little Green Tower is a compact "vertical farm" that uses a fine mist to deliver water, nutrients and abundant oxygen directly to the plant roots. Each 3D printed pod can hold up to 4 plants and pods can be stacked up to 4 high. The system requires only 10 liters of water and fits in a 30" x 30" footprint. The tower sits on a lazy Susan and can be rotated to access all of the plants from a single side.

A Raspberry Pi based controller measures the pH, conductivity, and temperature of the nutrient solution so that the nutrients can be maintained at optimal levels. A web based interface controls and monitors the system. It can even send a text when the water level is low!

This has been an ongoing project for several years and is still a work in progress. I will be filling in more details over the next few weeks.

For lack of a better place, the Instructions project section gives a detailed description of the system.

If you would like more information on the custom Raspberry PI board that controls the system, there is another project that covers it here.

first version time lapse no audio.mp4

This is a time lapse of the plant starter area of the first version of the tower. The lettuce leaves growing from below occasionally dissapear because they are being picked.

MPEG-4 Video - 4.86 MB - 08/01/2018 at 18:14

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2015_Nov_24.mp4

This shows a time lapse of the plants growing in an earlier prototype of the system. Note that this is ONE DAY of growth. The annoying black bars are caused by the interaction of the rolling shutter on the camera and the LED lights.

MPEG-4 Video - 4.60 MB - 08/01/2018 at 13:57

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ValveTest.webm

This video shows a test of the pinch valve which is used to control the sprayers. After clicking the link, you may have to hover over the picture and click play. When the pump is running and the valve is closed, it compresses a silicone tube and the sprayers generate mist in the pods. When the valve is open, the water drains from the system back into the base. The pump also runs with the valve open, in order to recirculate the water and add oxygen from "waterfall effect" as the water falls from the valve back into the base.

Open Web Media Project - Video - 3.54 MB - 08/01/2018 at 13:42

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  • 1
    Lettuce Begin

    It was a dark and stormy night (not really) in winter 2013 and I was in the produce section staring at some particularly bad lettuce.  Wilted would have been a kind description.  "There's got to be a better way!" I thought.  I had always been interested hydroponics, growing plants in water without soil, and figured that I could easily grow lettuce better than THAT.

    Researching existing hydroponic systems, I found they were bulky and expensive.  Being a typical engineer, I figured that I could make something better/faster/cheaper.  How hard could it be?  I determined that the most advanced systems use aeroponics, which sprays the roots with a fine mist.  Wanting to be at the forefront indoor agriculture, I began designing my own aeroponics system.

    The picture below should give you an idea how the system works.  Looking through a plant port in the side of a tower pod, it shows the roots after the lettuce has been growing for about 6 weeks.  The round object at the top of the frame is a mist sprayer.  The black square in the middle is one of the foam plant holders coming through the side of the pod.  The water drains through the stacked pods from top to bottom, and anything not absorbed by the roots ends up back in the bucket.

    Plant roots thrive in an oxygen rich environment but must remain moist.  The computer controls the pumps and valves to run a 10 second spray cycle every 5 minutes.  The computer, pods, foam,  and sprayers combine to give the roots an optimal growing environment.

    In the following entries, I'll describe the various parts that make up The Little Green Tower (LGT) and the design decisions made as the system evolved over the last five years.  The goal is to design a computer controlled, modular, compact, and low cost aeroponic system that is easy to replicate.  I encourage everyone to ask questions, since it can get boring just talking to myself.
  • 2
    How it Stacks Up

    The picture below shows the main portion of a three pod test system.  The pods are separated from eachother and from the base with four vertical links.  These minimize the amount of plastic and thus 3D printing time/cost to get the desired vertical spacing.  From top to bottom the tower has the following:

    1. Pressure Gauge
    2. Plant Starter Area
    3. Plant Pod A
    4. Plant Pod B
    5. Plant Pod C
    6. PVC Pipe Mounting Adapter
    7. PVC Pipe Base with Computer and Pump
    8. 200 Mesh Stainless Steel Water Filter
    9. Water Reservoir
    10. Pipe Base Aligner (inside the bucket)

    The tower has two valves, one in the plant starter area and one at the top of the PVC pipe base.  The top valve is normally open and automatically closes when the the system is pressurized.  The base valve is also normally open and closes to pressurize the system.

    Only a tiny amount of water flows through the sprayers when the system is pressurized.  In order to make sure that the water is well mixed,  the computer runs the pump for about 10 seconds at the beginning of a spray cycle with the top and bottom valves open.  This circulates water through the tubing and out the valve at the top.  The water cascades through the system and back into the bucket producing a "waterfall effect" that puts lots of oxygen into the water.  The computer then closes the bottom valve for 10 seconds to pressurize the system and run the sprayers.  At the end of the cycle the computer opens the bottom valve and the water in the tubing tubing drains back into the bucket.

    One of the key features of the system is that the entire column can be lifted out of one bucket and placed into a second bucket.  This makes changing the water very easy.  The buckets even have convenient handles!  The old nutrient mix is great fertilizer for lawns or shrubbery.  I'm still experimenting with the best water changing schedule, but it will probably be about once a month.
  • 3
    Keep Your Plants On

    Plants need something to support them while they grow.  Many hydroponic systems use foam since it can expand as the plant grows.  The LGT uses reticulated foam, which is a special type of open cell foam.  Open cell foam has open walls between all of the bubbles that make up the foam.  It is much more breathable than closed cell foam.

    In the first PVC pipe based version of the system, the foam was cut using the die in the picture below.  It produces a 2" cylinder with an "X" and hole in the center.  The hole is filled with carbonized bamboo fiber that extends beyond the foam, as shown in the second picture.  The fiber wicks moisture from inside the pod to the seeds when they are first planted.  Once I decided that the system could be 3D printed, I changed to square holes in order to avoid foam waste after cutting.  In this case, the same die is used with pre-cut square blocks, but only the "X" and hole portion in the center is cut.


    The foam is held in place by a 3D printed square collar as shown below.  A child-size silicone wrist bracelet provides a gasket between the plastic holder and the pod.  The picture in section 1 above shows an interior view of the plant holder where you can see the gasket.


    The picture below shows a plant that was removed after about 60 days.  As the lettuce grows, the largest leaves are picked.  The remaining leaves grow more quickly, since a larger root system is supporting a smaller number of leaves.   For the green leaf lettuce below, leaves can be picked starting about five weeks after the initial seeds are planted.  Small leaves can be picked at about 4 weeks.

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Chris Johnson wrote 08/01/2018 at 18:23 point

I added several time lapse videos and started a description of the system design in the "Instructions" section of the project.  I will be filling in the rest of the place holder sections as time permits.

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