A roadblock in hydroponically growing plants is feeding the correct ingredients at the concentration preferred by the plant.  The ingredients and concentration will vary depending on plant type.  I want to build an experience that automatically measures the ingredients.  For the prototype, I will focus on leafy green plants like lettuce, cucumbers, and tomatoes.  By not trying to measure chemistry for any hydroponically grown plant I will have more time to focus on the end-end experience.

The Goal

The goal of this post is to put down initial project definitions of what I’m calling – at least for now – the Ladybug Measure.

Thanks to Those That Went Before

Thanks to Ben Krasnow for posting his work on the Cookie Perfection machine.  A lot of my design thoughts come from watching Ben’s videos.  What a fantastic project with delicious results.

Thanks to Chris Gammell for pointing me in the direction of Ben’s work.  And of course for the excellent Contextual Electronics courses.  It’s exhilarating to take his courses and feel more like an apprentice to a master.  It is a great way to learn electronics.

What Ladybug Measure Does

The Ladybug Measure device will solve the challenge of measuring out the correct chemistry to hydroponically grow different types of plants.  The home farmer enters in the type of plant – say “Lettuce”.  The Ladybug Measure measures out the different dry ingredients into a container.  “Just add water” is the next step for the home farmer (hopefully RO water! 🙂 ).

High Level Design

I plan to evolve the design Ben Krakow used to build his amazing cookie machine.  The Ladybug Measure will be easier because it handles only dry ingredients versus the cookie machine which deals with hard to automatically measure stuff like brown sugar and butter.



Ben’s Cookie Machine Project

I like the “lazy susan like” approach.  So I’ll start with that design.  The Cookie Machine uses smaller quantities of dry ingredients.  I plan to use a funnel, but it will be bigger.  I’m not sure how much bigger.  The home farmer enters into a smart phone app that talks to Ladybug Measure over BLE.  I’ve started to use BLE and my iPhone for device UIs since I find the experience painless to create and use.:

  •  the plant to be fertilized. 
  • the gallons of water.
  • the smart phone app connects to an Arduino with BLE that is identified as a Ladybug Measure device.  It gives the command “please measure out ingredients for 1 gallon of fertilizer.”
  • Ladybug Measure moves one of the dispensers over the bowl.  The dispenser releases “just the right” amount of ingredient it holdsthe needed measured amount. so that the funnel will add some of the compound its holding into the bowl on the scale.

How Many Dispensers?

The short answer: 6

The longer answer…why?

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Really Big Dispensers…Labels Discussed Below

As noted in Fertilizer Management for Greenhouse Vegetables (Vol 3)  there are 16 elements needed by all plants:

The 16 elements required by all plants are carbon (C), hydrogen (H), oxygen (O), phosphorus (P), potassium (K), nitrogen (N), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), and chlorine (Cl).

…The nutrients N, P, K, S, Ca, and Mg are referred to as the macronutrients because they are required in larger quantities by the plant compared to the remaining elements. The other seven elements are referred to as micronutrients because they are required in small amounts, usually a few parts per million (ppm) in the plant tissue.

This would lead to a conclusion that I’ll need 16 dispensers….but wait…I’m going to cheat a bit.  MHPGardener has a youtube video on making nutrients for tomatoes.  He blends three compounds together:  CHEM-GRO TOMATO FORMULA 4-18-38Calcium Nitrate (CaNO3)Magnesium Sulfate (MgSO4).  I tried this blend and have been very pleased with results I have seen on my tomato plants.

I’ve decided I need a minimum of four dispensers one for each of the three compounds above and one other blend similar to the Chem-Gro tomato formula, but for leafy vegetables – CHEM-GRO LETTUCE FORMULA 8-15-36.

This prototype will support 6 dispensers.  Each dispenser holds at a minimum of 8 oz.  Slightly larger dispensers could be used.  I figured out the dispenser size based on a spreadsheet I made on Google docs (GitHub link) that determines the amount of ingredients needed given the type of plant and the amount of nutrient bath.

I imagine over time the amount of ingredients will grow.  For now, this should be perfect for the prototype.


That’s all for now.  I’m very excited to start on this project.  I am sure to learn a lot.  Also – I just got notice from OSH Park that Ladybug Sheild beta 2 boards are in the mail.  I should get them tomorrow.  YIPPEE!!



Thank you for reading this far.  Please find many things to smile about.