Soil Moisture Detection System

Theory:

Lower levels of moisture in the earth has less conductivity between two nodes. Higher levels of moisture in the earth has more conductivity between two nodes.

Landslides occur when gravity shifts a large mass of earth down a slope, exacerbated by excessive rain or an earthquake. In the case of this experiment, we can detect the excessive levels of water in soil through the amount of electricity conducted through the dirt.

Droughts occur when there is a lack of precipitation over a period of time. As the temperature increases, evaporation of the ground and water bodies increases, causing the ground to dry out, which causes the temperature to increase again. They also tend to set in over a long period of time. We can sense the dryness of the soil through this experiment as well.

Equipment:

• Two (2) crocodile clip wires
• One (1) micro:bit
• Two (2) stainless steel nails
• A power source (connection to computer, or battery pack)
• Soil samples (2 or more, one wet, one dry)

Practical:

To detect the level of moisture in the soil and predict landslide occurrences or alert imminent drought conditions.

We will be creating a circuit using two metal nodes and using the micro:bit to detect the amount of electrical current passing through the earth. In dry soil, a low amount of current will be picked up by the micro:bit. In wet soil, a high amount of current will be picked up.

1. Connect one end of a crocodile clip wire to the P0 pin and connect the other side to head of a nail.
2. Then connect the other crocodile clip wire to the 3V pin and connect the other side to the head of the other nail.

3. Connect the micro:bit to the computer to code in MakeCode.

a. In the forever block, place a [plot bar graph ( )] block and type 1023 into the second number input bubble. Input > [plot bar graph ( ) up to ( )]

b. Then, place the (analog read pin [P0]) block into the first number input bubble. Advanced > Pins > (analog read pin [P0])

A quick explanation: [plot bar graph] just means we’re using the LEDs on the front of the micro:bit to show how strong the current is. Less LEDs mean less current, a lot of LEDs mean lots of current. P0 is the pin that is receiving the current from 3V. We’re using the (analog read pin) because it’s an actual, physical pin we’re using. 1023 is the equivalent of the full 3 Volts, or the full power the micro:bit is handling at once.

4. Download the code and apply it to the micro:bit How do I put code onto micro:bit?

5. Test your creation with different types of soil by putting both nails into the same soil sample!

Questions:

Did you see a change when you put both nails into each soil sample type?

• If not, are you holding any metal parts of your design in both hands? Surprisingly enough, human bodies conduct low amounts of voltage so you may be affecting the results you get!
• What kinds of numbers did you get for each type of soil?
• Why do you think a higher amount of current is picked up through wet soil than dry?
  • Answer: The reason why is because electricity is conducted through the particles that are suspended IN water. Water allows the nutrients and metals in the soil to be spread out more evenly so the electricity can travel with less resistance than dry soil, where the conductible elements are less dispersed.
• How could you redevelop this into being more efficient with power? Print out a line of text rather than a graphic representation? How would you send this information to a research centre? What limitations do we have with this current design?