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 4 high. The system requires only 10L of water and fits in a 30" x 30" (76cm x 76cm) footprint. The tower sits on a lazy Susan and can be rotated to access everything from a single side.
A Raspberry Pi based controller measures the pH, conductivity, and temperature of the nutrient solution so that it 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!
If you like time lapse video of growing plants, make sure to check out the first few videos in the FILES section below.
As for the name, my wife said that I spend so much time on the system that the plants are like my "little green children", so of course they live in a Little Green Tower.
If you would like more information on the custom Raspberry PI board that controls the system, there is another project that covers it here.
This links to an interactive plot of actual EC/pH/Temperature data which is on display at plot.ly. Hover near the top of the plot for the controls. Click and drag on the plot to zoom a region. Drag the center of the tic labels to move the data. Drag on the ends of the tic labels to change the displayed range. This is the exact same type of plot that is on the web page served by the Raspberry PI controller.
This is a time lapse of some plants after they were moved down from the starter area. The front plant is initially about 2 weeks old and the side plants are about one week old. The following week is compressed into 1:30. A couple of leaves disappear in the middle of the video because I was doing some taste testing :-) .
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.
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
Lettuce seeds are very small, so tweezers are required for planting. Note that with my middle-age eyes, I need to use a magnifying visor to see the seeds well enough to grab them. The seeds are initially soaked in a shallow bowl to moisten them and increase the chance of germination. You have to actively sink the seeds, since they will float on top due to surface tension. Only seeds that sink the the bottom are used. If they won't sink, then they probably won't germinate.
After dampening the SOWqWICKs in water, use the tweezers to pull the seeds from the bottom of the bowl and plant them slightly apart in the fiber portion of the SOWqWICK. One end of the seed is very pointy and the other end is slightly rounded. The pointy end goes down. If you plant them pointy side up, the seeds may still still sprout, but the root may dry out and die before it can grow back into the fiber wick.
I'll post an update at the end the week with any progress. Note that this is the first time that I am testing the cellulose sponge blocks instead of the reticulated foam blocks, so the planting experiment could fail.
I added brackets above the plant holders to stop heavy plants from falling out.
I 3D printed a cover for the Raspberry PI and controller so that they don't get dripped on.
The picture below shows the setup I used for debugging a system crash issue that arose when running one minute spray cycles with the real pump and valve. It turns out that when you run the pump at for 30 seconds every minute, it gets a little warm, draws enough current to overwhelm the power brick, and crashes the Raspberry Pi. I've got a beefier power brick coming that should solve the problem.
I'm currently working on the Python software to interface with the EC/pH/Control board and also developing the web interface.
For testing, the spray cycles are running every minute. As you can see in the second picture, everything is sitting on my desk, so it's only running simulated spray cycles.
The approximately linear increase in conductivity over time is due to water evaporation. Since only pure water evaporates, the density of the dissolved ions left in solution increases, and that increases the conductivity.
I've made an EC calibration setup with solutions of various conductivities in cups that are hot melt glued to a base, in order to avoid spills. The pH probe is sitting in a standard pH 4 probe storage solution. The plot above shows that the pH is slightly temperature sensitive. A thermistor built in to the EC probe measures the temperature. The solutions are stabilizing to the same slowly changing room temperature.
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 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 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.
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:
Plant Starter Area
Plant Pod A
Plant Pod B
Plant Pod C
PVC Pipe Mounting Adapter
PVC Pipe Base with Computer and Pump
200 Mesh Stainless Steel Water Filter
Pipe Base Aligner (inside the bucket)
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.