Much Lettuce Machine: Aeroponic, Automatic Grow Box

I'd like to be the first farmer on Mars (seriously). One of the many questions I'll need to answer is: How much lettuce can you grow in a 50cm cube? This Instructable is a step in my quest to find out and overall prep for the trip:)

Some of the cooler things I've integrated are:

• productivity: with 18 grow sites, you can produce *a lot* of lettuce per cube
• practicality: total build cost per grow box is under $100 (+$100 more for remote control + monitoring), supplies are easily accessible, and you can configure the chambers to be stackable
• aeroponics: you're growing in fog!
• logging and active control: temperature, humidity, water level, and brightness are all logged and can be controlled via the web or in response to conditions
• multiple grow surfaces: 5 sides of the cube are a grow chamber, with lettuce growing towards the 'sun' in the middle
• *very bright* LEDs: most people don't have enough light in their amateur growing setups... not this time!

This project is my entry in the Growing Beyond Earth contest, 'professional' (term used very loosely) category:)

Supplies

To build your grow chamber, you'll need the following supplies:

• 1 x 27 gallon tote, ~$9
• 1 x 12 gallon tote, ~$6.50
• aluminum foil, $4 (you'll use <$.25 of it)
• spray adhesive, $10 (you'll use <$.10 of it)
• 17 x 2" cloning collar inserts, $12 (you'll use <$5 of them)
• 17 x 2" net pots, $11 (you'll use <$4 of them)
• 1 x ultrasonic atomizer, $12
• reflectix foam, $10 (you'll use <$.10 of it. doesn't have to be this, just something to make a float for the ultrasonic atomizer)
• 4 x LED light bulbs, daylight, $13.5
• 1 x LED light bults, soft white, $13.5 (you'll use <$3.4 of these)
• 1 x ac cord, $5 (to connect the lights)
• 1 x Fan, $10 (get a USB - ac adaptor, too)
• JB Kwik Weld, $5.5 (you'll use <$.5 of this)
• liquid electrical tape, $7 (you'll use <$.5 of this)

Add these to monitor:

• 1 x HUZZAH32 ESP32 board, $20 (get a USB-> ac adaptor and microusb cable too)
• 1 x STEMMA soil moisture sensor, $7.5
• 1 x VELM7700 light sensor, $5
• 1 x Si7021 temperature + humidity sensor, $9
• 1 x lithium ion battery, $12.5

And this to make remotely controlled:

• 1 x smart power strip, $28

And, these tools will come in handy:

• cordless drill
• soldering iron with solder
• table saw
• pull saw
• utility blade with spare blades
• tape measure
• silver permanent marker (so you can see it on the black plastic)
• masking tape

Step 1: Research

This project builds on a lot of work by others. The most influential/interesting I've found recently is the Space Buckets subreddit, in particular SAG's guides to lights. Also see this guide to Space-Age Gardening I wrote and this summary on Gardening Without A Yard. In particular, thanks to Tribe Awesome for sharing their amazing 5-gallon aeroponic project.

For specific plant conditions, look at seed companies and Cornell's Controlled Environment Agriculture program. High Mowing Organic Seeds and this hydroponic lettuce guide (pdf) are particularly useful.

Also, my Garduino / Growerbot / Soil IQ / Edyn projects coupled with Adafruit's many tutorials helped me figure out some of the sensing stuff.

Lastly, MIT has (had?) a super-interesting program making Personal Food Computers. They achieved an amazing result with basil: more flavor by growing under just UV! Unfortunately, it's unclear how real some of their results were:( But, let's learn from what we can and build upon it!

Step 2: Build a Grow Chamber

This contest specifically requires everything to fit in a 50cm cube, so I thought a lot about how to configure my plants vs. my lights. I was on the fence about putting plants in the middle surrounded by lights or lights in the middle surrounding the plants. Lights in the middle won out because this gives me more surface area on which to grow plants when they're young. In either configuration the leaves will crowd each other at high density, but I'd rather this happen when the plants are more grown and solve it by harvesting overlapping leaves vs. when the plants are young and some are possibly too crowded to grow at all. And, I really like the idea of a crazy bright LED ball in the middle:)

I want my grow chamber to:

1. Keep the roots in nutrients/water/air at the right ratios
2. Provide the right amount of light to the leaves
3. Make it easier to control things plants care about. At a minimum, we want to make sure temperature is OK, the roots don't dry out, and the lights stay on

Here's a useful overview for size etc. requirements for Outredgeous Lettuce.

I experimented with Cardboard Core Composite Fabrication, and I'm still excited by it. But, my results were pretty messy (I think my resin might have been too cold) and I gave myself multiple headaches. So, I'll wait until it's warmer and experiment more with this outside:) I've included a couple photos of what it looked like in case you're curious. If you experiment with this, please do so carefully and share your results!

What I ended up going with was part of a 27-gallon HDX storage tote with a piece of plywood + garbage bag liner as a divider + barrier to reduce the size to only 19 inches in length (we're a bit shorter on width and height). You can leave this out or do a smaller, partial-height divider if you're not specifically trying to use this grow chamber for this contest; with a smaller isolated chamber, you can place all the fans electronics etc. inside for a neater look and easy stacking (be careful to properly isolate electronics from water / fog).

The plants themselves live in part of a 12-gallon HDX storage tote. I used a pull saw + utility blade to cut it down to ~8.5 inches in height, and I used 2 of the 4 top corners as legs, attaching them with 3 screws each. The legs create room below the tote for the water reservoir + atomizer.

After cutting the 12-gallon tote to height, make holes in it for your net pots + foam collars using a 2" hole drill. Err on the side of more grow sites: you can always leave them plugged up to grow fewer.

You'll finish the grow chamber by lining the interior of the12-gallon tote and the lid of the 27-gallon tote with aluminum foil. Spray on adhesive and then put the foil against it, duller side facing the adhesive. The foil prevents us from wasting as much light: it reflects a lot of what hits it back to the plants. Poke holes with a pen and then use your fingers to tear / fold the foil away from the 2" openings, and you're done building your grow chamber!

Step 3: Make Fog

The atomizer is great, but it needs a float to sit just below the surface of the water. You can buy one, but it was out of stock and cost as much as the atomizer. So, I made my own out of a piece of bubble foil. See the photos for the rough size; I used hot glue to adhere it to itself + the atomizer. If you want this to last through a full grow, you'll probably want to use a more robust adhesive. I made 2 different ones, one with just bubble foil and the other with a chunk of aluminum can added. The foil one was simpler and worked better, so I went with it:) See the videos for examples of both running.

Place the atomizer in the 27-gallon bucket after adding water/nutrient mix before inserting the 12-gallon bucket; you'll want the cord running out a hole in the lid to the control electronics on the top.

Wils this work in space? Good question; I hope to find out:) If not, we can probably instead use small nozzles and pressure to produce small droplets.

Step 4: Let There Be Light, and Keep It Cool

I made a low-cost grow light out of 5 100-watt-equivalent (15*5 = 75 watts actual) LED bulbs, resulting in ~7500 lumens for .

I removed the LED board + drivers from the bulb, used JB-Kwik to attach the 5 boards together, soldered the wires together, and then added an AC power cord. I wouldn't suggest you do most of this: You don't need to remove the bulbs from the cases: this was a pain and mainly so I could have my wacky sun idea hanging in the middle of the grow chamber. Ditto with removing the plastic 'bulbs': upside is this gets you some more lumens reaching the plants,downside is this this makes the electronics dangerously exposed. I used liquid electrical tape to deal with this and masking tape to test this out for a few seconds, but this should be much more robust before running for any amount of time / unattended. Ditto on my method of hangin the LEDs into the grow chamber: a knot in the cord is definitely not adequate.

The fan's much simpler: a cheap USB fan taped above the LED 'sun', blowing air from outside the case onto the LEDs + plants. I'd definitely keep the fan running any time the LEDs are on to prevent them from overheating and provide fresh air to the plants. If you're modifying this design to stack, you'll want to mount the fan on the side.

Here's a rough calculator I made for you to figure out how many lumens you'll need to grow optimally. I expect it's making unreasonably-optimistic assumptions about how much of my light produced reaches the plants (vs. gets lost to absorption in the walls, escaping from the case, etc.). Also, note how much light you need: even with 75 watts for this small chamber, I could use more light if I want optimal conditions for more light-hungry plants like tomatoes or lights to be off sometimes (as some plants, including tomatoes, require).

For the next version, I'll probably make a custom light with some LEDs I bought from Cobkits. It'll cost more but it'll be *much* brighter, allowing me to reduce my photoperiod to the 12 hours required for the grow phase of the GBE contest.

Step 5: Monitor and Control

I used Adafruit.io as my dashboard + IFTTT to control the smart power strip; see above for my dashboard + an IFTTT rule on an outdoor greenhouse I did. You can do this locally with a relay board, and I'll probably add this as a redundancy on my next version. See Adafruit's tutorials for how to connect your sensors; everything's on i2c so it's pretty straightforward. My cobbled-together code for the HUZZAH32 (pretty much entirely Adafruit's samples) is here, too. Let me know in the comments if you want more details on this.

Step 6: Grow, Grow, and Grow Some Mo!

This is one of many attempts to grow food in new ways. Join the party: add your own ideas, and share your results! Above are photos of some more of my experiments. Please perform your own, and share your results. In spite of all the time humanity has been growing food, we still know surprisingly little about how to do it sustainably and automatically:)

Thanks for reading, and happy gardening!