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3.2 Plant Waterer

• Introduction

  All plants need 5 important ingredients in order to grow and flourish: light, air, water, nutrients, space (L.A.W.N.S).
  
  Plants can get light from the sun or from an artificial source, and air from the environment they are in, and so these are generally easy to come by. However; water, nutrients and space are 3 ingredients that can be harder to get right when trying to help your plant grow successfully.

  Sometimes when life gets busy or our routines change, we forget to water our plants. If a plant doesn't get the water and nutrients that it needs, it might not survive.
  
  So, what if we created a system to automatically water our plants when they need it?

  In this lesson, we will use a moisture sensor, and a 180° servo attached to a handcrafted container to create an automated plant watering system. As the moisture level in the soil drops, the servo will activate, watering the soil.
• Challenge 1
  Moisture Indicator

  The Challenge

  • The micro:bit will check the soil moisture level every 10 seconds.
    
  • When the soil moisture level is too low, show a frowning face on the micro:bit display.
    
  • When the soil moisture level is high enough, show a smiling face on the micro:bit display.

  Required Devices

  • 1 micro:bit
  • 1 sensor:bit
  • 1 soil moisture sensor

  Suggested Blocks

  • forever
  • show icon
  • pause
  • if true then else
  • 0 > 0
  • set [variable]
  • [variable name]

  Bonus Challenges

  • Have you ever heard a smoke alarm beep when its battery is running low? Could you update this project so that your plant beeps when it needs watering?
• Crafting Activity
  Build a Plant Waterer

  

  Crafting Supplies

  • 1 paper cup
  • 1 flexible straw
  • 1 pair of scissors
  • 1 stick of Plasticine

  Process

  1. First, cut a small hole in the paper cup with your scissors. The hole should just be big enough for you to poke through one end of the bendable straw.
     
  2. Next, cut the straw in half horizontally. Push the top half of the straw through the hole in the cup. Make sure you put the ‘straight’ part of this straw into the hole in the cup, and that the bendable part of the straw is outside of the cup by at least 2 centimetres.
     
  3. Using the Plasticine, attach the straw into the inside of the cup. You should try and plug the hole around the straw (inside and out) so that the cup is made watertight again. Make sure you don’t cover up the open end of the straw though, otherwise the water won’t flow through!
     
  4. Cut a few centimetres off the end of the other half of the straw that you haven’t used so far, then cut this piece vertically (along the length of the straw). You should end up with a curved piece of plastic.
     
  5. Wrap this piece around the glued straw, just above where the bendable part of the straw is. Using the Plasticine, attach the sides and top of this plastic strip to the rest of the straw. This will act as a pouch for the arm of the servo to sit in. The servo will then push the straw up and down when it is activated.

  Hints

  • If you don't have Plasticine, you can use a hot glue gun instead. If you're doing this, make sure you get an adult to help!
• Challenge 2
  Automatic Plant Waterer

  The Challenge

  • The micro:bit will check the soil moisture level every 30 seconds.
    
  • When the soil moisture level is too low, the servo will move to allow water to flow to the soil.
    
  • After 3 seconds the servo will return to its upright position, stopping the water flow.

  Required Devices

  • 1 micro:bit
  • 1 sensor:bit
  • 1 180° servo
  • 1 soil moisture sensor

  Suggested Blocks

  • forever
  • pause
  • if true then else
  • 0 > 0
  • set [variable]
  • [variable]
  • servo write pin
  • analog read pin

  Hints

  • The servo we are using uses quite a bit of power. It will not operate properly if the USB is connected directly to the micro:bit or if it is running off batteries. Upload code via the micro:bit, then plug the USB into the sensor:bit to test the servo.
    
  • If you're going to test this code with real water, make sure you test everything thoroughly dry first. You should also make sure you're testing with water where spills won't matter too much (like a kitchen) and get an adult's help.
    
  • If you're testing this project with a real plant, remember that for some plants too much water can be a bad thing, so don't put too much water on one plant in your testing!
• Conclusion

  In this lesson, we've combined our knowledge of the soil moisture probe and the servo motor to build an automatic plant waterer!

  In the next lesson, we'll combine several other technologies we've already used, and create an environment sensor!