Skill Sharing Workshop – Group 4

Wearable Hand Washing Timer

Angelina Do (3182746)

Valeria Suing (3182717)

For the video tutorial, please click on the link below:

Although washing your hands has always been important, the current state of the world has certainly brought to our attention the correct ways to do this action. According to the CDC: 

To prevent the spread of germs during the COVID-19 pandemic, you should also wash your hands with soap and water for at least 20 seconds or use a hand sanitizer with at least 60% alcohol to clean hands BEFORE and AFTER:

  • Touching your eyes, nose, or mouth
  • Touching your mask
  • Entering and leaving a public place
  • Touching an item or surface that may be frequently touched by other people, such as door handles, tables, gas pumps, shopping carts, or electronic cashier registers/screens. ” (CBC, 2020)

We can all remember some trends people came up with a year ago to make sure you scrub your hands for 20 seconds. However, singing your favourite song’s chorus repeatedly gets annoying, so we have the solution for you!

Introducing our Wearable Hand Washing Timer. This simple tutorial will teach you how to build this simple timer with materials that you probably already have at home. Let’s do this! 

Materials Required


From the class kit, you will need: 

  • Circuit Playground Express
  • Micro USB cable 

From your nearest crafting store, or your home, you will need:

  • Felt or any other non-conductive fabric
  • Scissors
  • Non-conductive thread 
  • Needle
  • Cotton balls 
  • Decorative elements (optional!)


  1. The first step is to download the following code: 
  2. Then you should connect your CPX to your computer via a USB cable and upload the code.
  3. Test it out and start building your wearable.
  4. Cut your felt or fabric in an approximately 17cm x 6cm rectangle.
  5. Attach your CPX in the middle of the rectangle with the non-conductive thread.                                                                                                                                                     img_1968
  6. Diffuse the lights using the cotton balls. You can sew them into the fabric so they can hold their place. Make sure to leave some space to connect the CPX to power.
  7. Secure the forearm band, customize with decorative elements, connect to power and wash your hands!

Further Explanation 

This code contains different custom functions that use the CPX LEDs to interact with the user. 

This code was modified from this source:

In “On start” we set the LED’s brightness to 10. Then we call the “blink” function to make the LEDs blink twice in green, and then we set them to “black” until the timer starts. The “blink” function is also used to make red LEDs blink once the timer is done. 

We were debating how to start the timer. Ideally, we would use a switch, but it had to be activated contactless for this purpose. After testing it in different ways, we decided to use “on tilt up” since it allowed us to start the timer without interfering with it later in the act of washing our hands (which was not the case with “on loud noise” or “on shake”). We also explored the opportunities to either use mapping or calibration, but it seemed to work best with just the set input instruction. 

Here’s a quick video of when we finally were able to find the best way to activate the timer:

The timer starts by calling on two other custom functions. Function prep_countdown sets LEDs to cyan and green to indicate the user how the lights will function as a timer. Function countdown is the timer itself. For this, the function uses a counter and sets LEDs to either magenta or blue to indicate that a second has passed. We decided to add sound once the timer was done, along with the blinking of red lights. This allows the user to pay attention to washing their hands instead of staring at the timer all the time.

To customize the timer, the user could change the parameters when calling the function. In this case, we used 20 seconds since that is the recommended time to wash your hands. 

Overall, we had fun working on this project and exploring what we had at home to build this fun and useful wearable. 


Adafruit. (2020, April 1). No-Touch Hand Wash Timer for Circuit Playground Express and CLUE. Adafruit Learning System.

CDC. (2020). When and How to Wash Your Hands. Handwashing | CD

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