Click a Button Without Your Hands: Design a Puff Switch

This project follows the Engineering Design Process. Confirm with your teacher if this is acceptable for your project, and review the steps before you begin.

Write Your Code

Before you build your puff switch, you can write a very simple program to test basic "switch" functionality on the micro:bit.

1. If this is your first time using a micro:bit, follow the Getting Started instructions on the micro:bit website to learn how to use your micro:bit and connect it to your computer. 
2. Decide what programming language you will use for your micro:bit:
   1. If you are new to coding, we recommend using Microsoft MakeCode to program your micro:bit. MakeCode is a graphical programming language where you make computer programs using colored blocks of code instead of a text editor. The example code in this procedure uses MakeCode. We recommend following a few of the MakeCode tutorials before you proceed.
   2. You can also program your micro:bit in Python, JavaScript, and Scratch. You may prefer this approach if you already have programming experience in one of these languages. See the Let's Code page for more details.
3. Connect a single alligator clip to micro:bit pin 0 as shown in Figure 2.

Image Credit: Ben Finio / Science Buddies

Figure 2. Micro:bit with one end of an alligator clip connected to pin 0.

4. Write a simple program like the one shown in Figure 3. This program will make a smiley face when you touch the other end of the alligator clip to the micro:bit's 3V pin. When the alligator clip is not touching, the LED grid will be blank. 
   1. The set pull pin P0 to down block ensures that pin 0 reads "low," or zero, when nothing is touching it. 
   2. The digital read pin P0 block reads the state of pin 0. It will return "high," or one, when you connect it to the micro:bit's 3V pin. Otherwise it will return zero.
   3. The if/else block decides what to do depending on whether pin 0 reads 1 or 0.
      1. If pin 0 reads 1, show a smiley face icon.
      2. Else, if pin 0 reads 0, clear the screen.

Image Credit: Ben Finio / Science Buddies

Figure 3. Code for simple switch testing.

5. Test your program by touching the free end of the alligator clip to the micro:bit's 3V pin. Your micro:bit should show a smiley face (Figure 4). When you release the alligator clip, it should go back to a blank screen.

Image Credit: Ben Finio / Science Buddies

Figure 4. Micro:bit with the other end of the alligator clip connected to the 3V pin.

6. Think about what other output(s) you might want to program to respond to your switch and experiment with them.
   1. You can play music and sounds using the blocks in the Music menu.
   2. You can show text or other icons using the blocks in the Basic menu. 

Design and Build Your Puff Switch

Now that you have code for a basic switch working, you can build the mechanical structure for your puff switch.

1. Electrically, your puff switch is no different than the simple circuit you made with a single alligator clip in the previous section. You can demonstrate this as follows:
   1. Connect two alligator clips to the micro:bit - one to pin 0 and one to the 3V pin.
   2. Touch the free ends of the alligator clips together. Your micro:bit should display a smiley face just like it did in the previous section.
   3. Cut two small squares of aluminum foil. Clip the free end of each alligator clip to one square, then touch the squares together (Figure 5). Since the alligator clip wires and aluminum foil are all conductive, they form a closed circuit between pin 0 and the 3V pin.

Image Credit: Ben Finio / Science Buddies

Figure 5. Closed circuit formed with alligator clips and aluminum foil.

2. Now, your engineering challenge is to build a puff switch so you can make the two pieces of aluminum foil touch by blowing into a straw. It may take some experimentation to build a switch that works "just right." When you blow through the straw, the two pieces of aluminum foil should touch, forming a closed circuit. When you stop blowing, the two pieces should come apart, forming an open circuit. Figures 6, 7, and 8 show an example device from several different angles, but you do not have to build one that matches the figures - you might think of a better design! Remember that you can also refer back to Figure 1 in the introduction for a diagram showing how your switch should operate.
   1. A large piece of cardboard is used as the base.
   2. A vertical support is attached to the base with hot glue, and a piece of aluminum foil is taped to this support.
   3. Thin cardboard supports form an archway to hang the moveable piece of aluminum foil.
      1. The piece of aluminum foil is not a square - it has a long extension on one side to allow a connection to the alligator clip (not pictured). 
      2. This piece of aluminum foil is taped to a piece of cardboard with a piece of clear office tape, and a small gap in between the aluminum foil and cardboard. The flexible tape acts like a hinge.
      3. The piece of cardboard is attached to the supports using binder clips instead of hot glue. This lets you easily swap out the part if you want to test different designs (different size pieces of aluminum foil, gap widths for the tape, etc.).
   4. The straw is held in place using cardboard supports. A flexible straw lets you more easily bend the mouthpiece toward the user. 

Image Credit: Ben Finio / Science Buddies

Figure 6. Rear view of puff switch device.

Image Credit: Ben Finio / Science Buddies

Figure 7. Side view of puff switch device.

Image Credit: Ben Finio / Science Buddies

Figure 8. Front view of puff switch device.

3. Connect the alligator clips to your aluminum foil. The alligator clips are heavy and can get in the way - make sure they will not interfere with operation of the device. Figure 9 shows the alligator clip connections. Note how the red alligator clip is connected to the extension coming off the top of the moveable piece, not the part that rotates.

Image Credit: Ben Finio / Science Buddies

Figure 9. Alligator clip connections to puff switch.

3. Blow through your straw and make sure the two pieces of aluminum foil touch. Figure 10 shows a close-up. If you cannot easily see your micro:bit while blowing through the straw, it will help if you program it to make a sound so you can confirm that your switch works.

Image Credit: Ben Finio / Science Buddies

Figure 10. A close-up view of the puff switch while blowing air through the straw. Note how the two pieces of aluminum foil are touching.

4. If your switch does not work (it does not trigger the output on the micro:bit), you will need to identify the problem. Remember that you need a closed circuit on the entire path between pin 0 and the 3V pin for your switch to work properly. A break anywhere on that path will cause an open circuit and your switch will not work. Here are some things to watch out for:
   1. Make sure all alligator clip connections are secure.
   2. Watch out for any rips or tears in the aluminum foil, especially the thin strip at the top of the moveable piece.
   3. Make sure that the two pieces of aluminum foil are coming into firm contact with each other. The more contact, the better. You might need to change your design, for example by making the pieces bigger or closer together.
5. Think about ways you can improve your puff switch's performance or make it easier to use. See the Variations section for more ideas.