The sys admin's daily grind — PomodoPi

Green Garden

Article from Issue 177/2015

Charly starts the tomato and dill season aboveground with a traffic light and underground with a soaker hose, along with assistance from two gardeners and the ubiquitous Raspberry Pi board.

Truth be told, I have ignored my garden for the past 15 years. This year, however, I set myself the task of growing my own tomatoes and herbs, and I wrote on Twitter about possible technical support for my green thumb. This was duly noted by gardeners Vanessa Giese and Pia Reichert in their blog [1]. Shortly thereafter, I was a guest author for the "Garden Nerds" column.

My first step was to plan automatic irrigation. My daily bread as a sys admin is to automate routine tasks with bits of technology, so I searched and found a soldering iron and tied a capacitive humidity sensor up to an A/D convertor using a Raspberry Pi. This setup provides me with data about the soil moisture in the plant pot every minute [2].

My Raspberry-to-garden adapter forms the second phase: I have a short hose running from the faucet in the garden to a solenoid valve. While the Raspberry Pi has 12 volts at its terminals, it lets water through, which flows into a perforated hose that I have looped through my raised bed. The tomatoes will put down roots there as soon as the danger of frost is over. When I wrote this article, however, they were enjoying their winter quarters in my living room (Figure 1).

Figure 1: Legal plants with Raspberry Pi (right) and a traffic light reminiscent of Nagios (left).

Floral Lights

Because I am still watering manually, I need something to remind me to do it – a traffic light that is about 40cm tal [3] for the USB port. The control software called "Clewarecontrol" can be found online [4]. I have programmed it so that the traffic light is green when the soil moisture is greater than 65 percent, yellow between 55 and 65 percent, and red if the moisture level falls below that – the plants have survived so far.

The last phase of the project is, provisionally, a webcam to watch the plants. I am using the one from the Raspberry Pi Foundation without the infrared filter, which comes with a blue filter foil. Photosynthesis activity can be detected in this spectrum range based on the brightness distribution, which is something I learned from NASA [5].

I have documented the details of my project in an ongoing series of articles [6] on the gardeners' blog. If the traffic lights give me an evening off, I would be grateful for posts from other garden nerds.


  1. Gardeners' blog: (in German)
  2. Soil moisture progression from Charly's plant cultivation: (in German)
  3. Cleware USB traffic light:
  4. Clewarecontrol:
  5. The Landsat Program:
  6. Charly's article: (in German)

The Author

Charly Kühnast is a Unix operating system administrator at the Data Center in Moers, Germany. His tasks include firewall and DMZ security and availability. He divides his leisure time into hot, wet, and eastern sectors, where he enjoys cooking, freshwater aquariums, and learning Japanese, respectively.

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