Microgravity Plant Grower "Disco Ball"

Introduction: Microgravity Plant Grower "Disco Ball"

About: Currently a Systems Engineer at Sagentia, with 3+ years of experience in consumer audio electronics. I Graduated from The University of Kent with a MEng in Electronic & Communications Engineering.

Hello readers, this project is a professional submission to the Growing Beyond Earth Maker Contest.

This project is a proof of concept for a potential planter design that could be used to grow plan in microgravity.

Based on the contest rules I listed the requirement of the system,

  1. System must fit in a 50cm^3 area.
  2. System must take advantage of microgravity.
  3. System could be orientated in any position
  4. System can be source power externally from the ISS internal power rails.
  5. System must automate much of the growing process with minimal interaction from astronauts.

with the above assumptions I began designing the system.

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Step 1: Project Proposal

To start off I drew a rough outline of what I thought the system could look like,

The initial idea I had was an orb suspended in the centre of the growing environment with lighting mounted on the surrounding frame.

The base of this box would house the water & electronics.

At this stage I began to list the sort the potential components of such a system,

  1. Frame - Would need to select a suitable frame material
  2. Lighting - What type of lighting would be best? LED strips?
  3. Sensors - For the system to be automated it would need to be able to sense moisture things like moisure & temperature.
  4. Control - The user would need a way of interacting with the MCU

The goal of this project is to produce a proof of concept, based on the lessons learned I will make a list of future work & development required to take this idea further.

Step 2: Proof of Concept - BOM

The BOM (Bill of Materials) for this project will cost approximately £130 to order everything required, of that cost roughly £100 will be used to make a single plant grower unit.

It’s likely that you would have a fair chunk of the electronics components dramatically reducing the code.

Step 3: Electronics - Design

I've used Fritzing to plan the electronics required for this project,

The connections should go as follows,

LCD 16x2 I2C

  1. GND > GND
  2. VCC > 5V
  3. SDA > A4 (Arduino)
  4. SCL > A5 (Arduino)

Rotary Encoder (D3 & D2 were selected as they are the Arduino Uno Interupt pins)

  1. GND > GND
  2. + > 5V
  3. SW > D5 (Arduino)
  4. DT > D3 (Arduino)
  5. CLK > D2 (Arduino)

DS18B20 Temp Sensor

  1. GND > GND
  2. DQ > D4 (Arduino, with a 5V pull up of 4k7)
  3. VDD > 5V

Soil Moisture Sensor

  1. A > A0 (Arduino)
  2. - > GND
  3. + > 5V

Dual Relay Module

  1. VCC > 5V
  2. INC2 > D12 (Arduino)
  3. INC1 > D13 (Arduino)
  4. GND > GND

for the other links please look at the diagram above.

Step 4: Electronics - Assembly

I assembled the electronics as described in the previous page's diagram,

I used the protoboard to make a shield for the Arduino Uno,

To do this I broke the board to roughly the size of the Uno then added male header pins that aligned with the female headers on the Uno.

If the connections match the previous diagram the system should work correctly, it might be a good idea to layout the connections in a similar fashion to me for simplicity.

Step 5: Software - Plan

The general idea for the software functionality is for the system to continuously loop around reading the sensor values. On every cycle the values will be displayed on the LCD.

The user will be able to access the menu by holding the rotary switch down, once this is detected the menu UI will open. The user will have a few pages available,

  1. Start Water Pump
  2. Toggle LED State (On / Off)
  3. Change System Mode (Automatic / Manual)
  4. Exit Menu

If the user has selected Automatic mode the system will check if the moisture levels are within the threshold value, if they are not it will automatically pump water wait a fixed delay and re-check.

This is a basic automation system but will work as a starting point for future developments.

Step 6: Software - Development

Required Libraries

  • DallasTemperature
  • LiquidCrystal_I2C-master
  • OneWire

Software Notes

This code is the first draft code which gives the system basic functionality, it includes

See the attached Nasa_Planter_Code_V0p6.ino for the latest build of the system code,

Temperature & Moisture readings on display.

Automatic Mode & Manual Mode - User can make the system auto pump water at a threshold moisture

Moisuture Sensor Calibration - AirValue & WaterValue cont int need to be manually filled as each sensor will be slightly different.

User Interface for controlling system.


Step 7: Mechanical - Design (CAD)

To design this system I used Fusion 360, the final assembly can be viewed/ downloaded from the link below

https://a360.co/2NLnAQT

The assembly fits into the contest area of 50cm^3 and has used PVC pipe to construct the frame of the box, with 3D printed bracket for the corner joins. This frame has more 3D printed parts that are used to mount the enclosure walls & LED lighting.

In the centre of the enclosure we have the planter "Disco Orb" which is a 4-part assembly, (2 half’s of orb, 1 base of orb, 1 tube). This has specific cut-outs to allow the water pump pipe & capacitive moisture sensor to be inserted into the soil section.

At the base of the design you can see the control box, this houses the electronics & gives the frame rigidity. In this section we can see the User Interface display & Controls.

Step 8: Mechanical - 3D Printed Parts

The mechanical assembly requires various 3D printed parts,

Corner Frame Brackets, Side Panel Mounts, Door Hinge, LED Mounts & Control Box Brackets,

These parts should roughly total 750g of weight and 44 hours of print time.

The parts can either be exported from the 3D assembly linked on the previous page or can be found on thingiverse here,

https://www.thingiverse.com/thing:4140191

Step 9: Mechanical - Assembly

Note that my
assembly I skipped the enclosure wall parts, mostly due to time & cost limitations,

First off, we need to cut down the PVC Pipe down to 440mm sections, we will need 8 sections of pipe like this. 8 LED Mounts Printed & 4 Frame Corner Brackets.

Now we need to prepare the LED strips,

  1. Cut down the strips at the scissor marks at roughly 15cm lengths, we need to cut 8 sections of LED strip
  2. Expose the + & - Pads by removing a bit of rubber
  3. Solder down the male header connectors (Cut sections of 3 and solder each end to a pad)
  4. Remove the adhesive protector on the back of each strip and attach to the LED mount 3D printer parts.
  5. Now make a cable to link up all the positives & negatives of each strip
  6. Finally power it up and check that all the LEDs are working

Step 10: Project - Progress So Far

So far this is as far as I have got through the assembly of this project,

I plan to continue updating this guide as the project develops,

Whats left to do

  • Complete control box assembly
  • House Electronics
  • Test water pumping System
  • Review progress


Step 11: Lessons Learned

Even though as of now the project has not been completed, I have still learned a few important things from researching this project.

Fluid dynamics in Microgravity

This is an amazingly complex subject, which introduces lots of unseen issues for standard gravity-based fluid dynamics. All of our natural instincts for how fluids will act go out of the window in microgravity and NASA have had to re-invent the wheel to get relatively simple earth-based systems to function.

Moisture Sensing

Learn about the different methods that are commonly used for moisture detection (Volumetric Sensors, Tensiometers & Solid State, see this link for a good read on the topic https://mytrellis.com/blog/smstypes)

Minor Notes

PVC Pipe is excellent for quickly building frames,

I need better woodwork tools!

Plan ahead on hobby projects, segment tasks and set deadlines just like at work!

Step 12: Future Work

After reading up on how we manage fluid dynamics in microgravity I’m very interested in designing my own solution for the problem,

I would like to take this rough design further, the idea for this system is to use a bellows tank with stepper motors that can compress the container area to maintain a certain pipe pressure.

Step 13: Conclusion

Thanks for reading I hope you enjoyed, if you have any questions or would like help with anything covered in this project feel free to comment!

Jack.

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