We got wind (via Twitter DM) of a team from Tynecastle High School who have reached the finals of the annual PA Raspberry Pi Competition. The TynecastleTechs are competing in London TODAY, and we wish the students and the teachers who have helped them the best of luck. They have built an aquaponics system on a small scale that allows users to grow their own plants without soil, instead using fish waste as a source of nutrients. A Raspberry Pi controls the pumps and monitors temperature and pH, alerting users if they vary outside of the optimum range.
Fishing for info
Aquaponics for Beginners was the textbook that started the team on their journey towards building their own aquaponics system. They learnt how bacteria convert fish waste into nitrates that fertilise plants, and about the types of fish that could thrive in such a system. Staff at local aquarium shops, as well as a horticultural expert family member, advised on the plants that could grow well.
Filling the tank
Research led the team to select the Scissortail Rasbora, since this is a hardy and adaptable fish that can live in a smaller tank. They moved twelve scissortails into in a 40-litre plastic tub, along with aquatic plants to create a more natural environment and provide hiding places, reducing stress for the fish. They selected Java moss, Anubias, and Cryptocoryne as the most suitable plant species for smaller tanks, and added some mature specimens. The team kept the water heated to tropical fishes’ favourite temperature (about 24°C or 75°F), and also installed appropriate filters.
The school’s CDT department stepped in to help by drilling holes in an acrylic sheet to use as a fish tank lid. This allowed the team to run power cables and water pipes through it, and also feed the fish through it.
Aquaponics in action
To show aquaponics in action, the students needed to grow new plants successfully from seed in their system. A horticultural expert suggested watercress as the best choice because it grows well in water, and slightly faster than other plants. The TynecastleTechs team chose a long plastic windowbox as a container for the plant bed — this would allow water to flow along the entire length, delivering nutrients and promoting even growth. They added clay pebbles to provide a bit of stability for the plants and allow them to weave their roots around them.
Let there be light
The students needed a light source so the plants could get on with their job of photosynthesising. They chose indoor grow lights — they found that these generate more power than regular LEDs, and this would increase the rate of photosynthesis.
They wanted to control the UV light in a cycle, to simulate day and night. This would allow the plants to “know” when it was time to perform photosynthesis, and when to have a rest from that and get on with other important plant metabolism stuff. Their original plan was to connect a timer to the Raspberry Pi’s GPIO pins and write some code in Python to operate it, but they ran out of time and went for a more expensive lighting strip with a built-in timer.
Raspberry Pi gets water flowing
In the system’s water cycle, pumps move water from the fish tank to the plant bed and from the plant bed to the fish tank, sharing nutrients between the two — that’s aquaponics in action. The pumps are connected to a relay network so the Raspberry Pi controlling the system can communicate with them. The students coded a timer in Python that makes the pumps transfer water from the fish tank to the plant bed for 15 minutes, then drain from the plant bed to the tank for one minute, and then stop for 44 minutes before starting all over again.
Most importantly for this competition, the team needed to find a way to monitor the aquaponics environment and demonstrate that their electronics are working as intended. They chose pH and temperature sensors as the most useful ways to provide real-time data on the system’s status. They wired up a waterproof DS18B20 temperature sensor directly to the Raspberry Pi. Some Python code monitors its output and triggers a buzzer if the temperature reading is too high or too low. There’s also Python code to monitor the pH sensor readings.
Show us what you’re working on
Well done to the students on the TynecastleTechs team and their teacher Mrs Holt. We’re looking forward to seeing how you get on in the competition!
We love seeing how you genius teachers and other school staff use Raspberry Pi into your classrooms, so do leave a comment to share what your young engineers have been working on.