The system is based in two sensors. Each sensor is built using galvanized nails connected to an analog port and making a resistor division with another resistor. The sensors also keeps the nail separated in a distance equivalent of 1.5 inches using pieces of foam that I found in the trash. Yes! the system is simple, cheap and you can monitor your soil only using nails. I choose galvanized for obvious reasons.. I do not want to see the nails rusted in a short period of time.
This is more than enough to check if soil has water in good amount to the plants or not. Considering was a fair, I build a LED matrix in order to show a happy or sad face. This face has a push button as well.
If "one eye" is on, means sensor number ONE. Two "eyes" means sensor number TWO. The sensor selection was done using the push button. On this way, you could see "one" or "two" eyes being switched by the users. In the fair, I had two coups each of them with soil but one of them with a little bit of water and each coup connected to a sensor.