How Does Distance Affect Wireless Signal Strength?

This project follows the Scientific Method. Review the steps before you begin.

Program Your Micro:bits

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 a micro:bit and how to connect it to your computer. 
2. Decide what programming language you will use:
   1. If you are new to coding, we recommend using Microsoft MakeCode to program your micro:bits. MakeCode is a graphical programming language that lets 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 starting your project.
   2. You can also program your micro:bits in Python, JavaScript, or 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. Start a new MakeCode program. Call it "Transmitter." This program will make one of your micro:bit boards send a radio signal when you press one of the buttons. 
4. Drag out blocks to build the program shown in Figure 2. 
   1. Inside the on start block:
      1. Put a radio set group 1 block. You will set both micro:bits to the same radio group to make sure they can communicate with each other. 
      2. Put a radio set transmit power 7 block. This sets your micro:bit's radio to maximum power (you can set the power level between 0-7).
   2. Add an on button A pressed block. Add the following blocks inside it:
      1. play tone middle C for 1 beat until done: This plays a short musical note to confirm when you have pressed the button.
      2. radio send number 0: This makes the micro:bit broadcast the number "0" as a radio signal.
      3. show icon  (check mark): This makes the LED grid on the micro:bit show a check mark to confirm that the message has been sent.
      4. pause (ms) 1000: This makes the check mark stay on the screen for 1 second. One millisecond (ms) is 1,000 seconds. You can change the number if this feels like too long (or too short).
      5. clear screen: This turns all the LEDs off again. Without the pause (ms) 1000 block, if you cleared the screen, the check mark would flash too quickly for you to see and then disappear. 

Image Credit: Ben Finio / Science Buddies

Figure 2. Code for transmitter. 

5. Download this program to one of your micro:bit boards.
6. Unplug the board from your computer and plug in the battery pack.
7. Press button A to confirm that the program works. 
8. Start a new MakeCode program and call it "Receiver." This program will make your other micro:bit board display the strength of the received signal when it receives a message from the transmitter.
9. Drag out the blocks to build the program shown in Figure 3.
   1. Inside the on start block, add a radio set group 1 block. This makes sure your receiver is part of the same radio "group" as the transmitter. 
   2. Add an on radio received receivedNumber block. The code in this block will happen when the micro:bit receives a number from another micro:bit. Inside the block, add:
      1. play tone low C for 1 beat until done: This makes your micro:bit play a sound to confirm that it has received a signal. (You can pick a different tone if you want.)
      2. show number received packet signal strength: This will make the micro:bit display the signal strength of the received message on the LED grid. Since the micro:bit only has a 5x5 grid of LEDs, it cannot display the entire number at once. The number will scroll across the screen.
10. Signal strength is measured in units called decibel milliwatts, abbreviated dBm. These units can be a little confusing for a couple of reasons:
    1. First, they are negative. A number that is farther away from zero (more negative) means a weaker signal. A strength of -50 dBm is typically considered very good—you would be able to stream HD videos, do video calls, or play games with no trouble. A strength of -90 dBm is a very weak signal—you might not even be able to make phone calls or send text messages. 
    2. Second, because the units follow a logarithmic scale. Every increase of 10 dBm means that the signal strength increases by a factor of 10. For example, a signal strength of -60 dBm is ten times stronger than a signal strength of -70 dBm. You do not have to worry about this too much for this science project. Just remember that a "bigger" negative number (a number that is farther away from zero or has a larger absolute value) means a weaker signal. 

Image Credit: Ben Finio / Science Buddies

Figure 3. Code for receiver.

Conduct Your Experiment

1. Set up your micro:bit boards so that the receiver is at one end of a tape measure or meter stick (Figure 4). Since you will not need to move it, you can leave your receiver plugged into the USB cable for power, but you can also use a battery pack.

Image Credit: Ben Finio / Science Buddies

Figure 4. Receiver micro:bit set up next to meter stick.

2. Make a data table like Table 1.

3. Decide what orientation you will keep your micro:bit boards in for the experiment. It is important to keep this constant for all of your trials. For example, you could have the two micro:bit boards facing each other (so the LED grids are facing toward each other), or facing away from each other (so the back of one board is facing the front of the other board), but you should be consistent.
4. Place your transmitter board as close as possible to the receiver board. (It is OK if the boards are touching.)
5. Press button A on your transmitter board. Listen for the beeps to confirm that the message has been sent and received. 
6. Watch the LED grid on your receiver board. Record the signal strength in your data table.
7. Repeat steps 5-6 two more times, for a total of three trials at this distance.
8. Move your transmitter board 10 cm farther away and conduct three more trials, repeating steps 5-6 three times at the new distance. 
9. Keep moving your transmitter board farther away, conducting three more trials at each distance, until the signal strength stops changing or the receiver board stops receiving the signal completely. 
10. Analyze your data.
    1. Calculate an average signal strength for each distance. To do this, add up the three signal strength readings and divide by three.
    2. Make a graph with distance on the horizontal axis and average signal strength on the vertical axis. Remember to label your axes and include units. 
    3. How does signal strength change with distance? Does this match your prediction?
    4. How can you relate your results to everyday experience using wireless devices? Have you ever noticed how the strength of your signal (or resulting speed of your connection) changes depending on how close you are to a Wi-Fi router or cell tower?