Prototype Test - Take One

After months of research, design, and purchasing hardware, I finally have a working prototype of an automated hydrogarden. Having said that, it does not have everything that was planned; these items will be added in subsequent tests. Components not included in this test include water monitoring equipment, a camera, and a dedicated scheduling device (i.e. Raspberry Pi with a control program). More importantly, this prototype does include a water aeration system, lighting suitable for plant growth, and an automation program.

Hardware

Fig.1 - Preliminary hardware setup

I will begin by describing the hardware setup. The main load-bearing devices include an aquarium pump which aerates the water and an overhead light constructed specifically for plant growth. Both devices are attached to X10 appliance switches (see Fig.2), which allows them to be activated/deactivated from a computer; I will discuss this in more depth later. The water reservoir (see Fig.3) is ~500 mL in volume and has two holes in the top: one for the aeration tube and the other for the actual plant. The seeds are planted into a small sponge (the inert medium) which will provide the future plants with structural support. The reservoir is filled with Hoagland solution, which will be the topic of another blog post. The reservoir is placed in a heated dog dish as Canadian winters are quite cold, meaning that, during the night, the temperature of the seeds may drop below the 15°C needed for germination. The hardware design is very similar to that of the elaboration phase, albeit with a few exclusions.

Fig.2 - X10 switches and transceiver

Fig.3 - Close-up of the reservoir

Software

Now, onward to the software. Currently, I am using a program I call hydrocontrol to control automated aspects of DotSlashGarden. It is written in bash and is simply a wrapper for bottlerocket, a Linux-based command-line utility for controlling X10 Firecracker devices. It is extremely simply and I only created it because I can never remember the syntax for bottlerocket!

As an example, this would turn on the light:

# hydrocontrol -l on

hydrocontrol must be run as root as it requires access to serial devices (i.e. the X10 Firecracker module). Whilst this program is able to turn devices on or off, it is unable to do any type of scheduling; another program, such as cron, would be required to do such a task.

As you can see, this is much simpler to remember than:

# br -c A -n 1 -x /dev/ttyUSB0

If you would like to look at or use this program, it is available on my Dropbox. It should be noted that it is somewhat kludgey and it could easily be rewritten in 15 minutes; however, it does the job, and that is what is important.

Conclusion

With this test, I hope to identify some issues will the implementation so that they can be fixed as soon possible. I have already learned that small reservoirs are much easier to handle as 0.5 L of Hoagland solution is easier to make than 14 L. In order to move on to another prototype, the main control program (garden) needs to be integrated into the Raspberry Pi with features such as logging and serial control. Furthermore, the Raspberry Pi also needs to have networking support (something which has been eluding me as of late...).

At this moment, the seeds, which are of the lettuce variety, are germinating. In about a week or so, they should sprout and the real test of DotSlashGarden's growing abilities will commence.

Conditions for Germination

Before beginning a test of the current hydrogarden components, it is important to understand what a plant actually needs in order to grow. One area that I have not researched in this regard is germination.

There are many elements that a plant needs to begin germination. For this blog post, I will label them according to importance: required, preferable, and non-essential.

Required

• Water

Water is needed to soften the hard seed coat, which will allow a future sprout to grow. Water also allows the food reserve in the seed to be used. It should be noted that the seed only needs enough water to moisten it; it should not be submerged in water.

• Oxygen

As an aerobic organism, plants need oxygen to survive much like humans and various other organisms. Oxygen uptake may only occur after the seed coat has been softened, depending on the type of plant. Atmospheric oxygen should be sufficient, making aeration unnecessary.

• Heat

Most plants will germinate at temperatures in the range of 15 - 24°C.

Preferable

• Heat

For vegetables, the ideal temperature range is 24 - 32°C. As the first plant I will be growing is lettuce, this range is suitable.

Non-Essential

• Light

Most plants do not require a light source for germination to begin. The main types of plant that do are forest plants, which are not good candidates for hydroponics.

• Nutrients

Because a seed contains its own food supply, addition nutrients do not need to be added at this time.

Conclusion

When designing a testing procedure for the current hydrogarden, I will keep these elements in mind to ensure that the seeds will germinate. If the seeds do not germinate, I will look back at this list to check if the conditions are met.

The next blog post will outline the testing set-up, including the components and the implementation.