Creating a 25-minute Pomodoro timer with the BBC micro:bit

15 December 2020

I recently came across the Pomodoro Technique for time management, which suggests you focus on a particular task for 25-minute periods, with short breaks in between the 25-minute sessions. The aim is to reduce interruptions and help to achieve flow, when you are fully in the zone and focused on a task. Pomodoro is Italian for tomato, and the technique is named after the tomato-shaped kitchen timer that the technique's author, Francesco Cirillo, used.

I have found this technique useful in the past, and was thinking about getting a timer to help me with it. There is a nice online pomodoro timer here, and there are countless phone apps available (some on subscription). Ideally, I wanted something I could see all the time, without having to fiddle with my phone, or give over screen space to an on-screen counter. A kitchen timer would probably be noisy, clicking away as it counted down the time. Sand timers are appealing, but only show the time remaining approximately. There are some nice desktop timers, like the one pictured, but I wasn't sure I wanted the clutter.

So, I coded my own pomodoro timer using the micro:bit. The device is a really good fit for this application in many ways. Most obviously, it has 25 LEDs, which is one for each minute of the work session we're timing. I already had one here too, so it was easy to try it out. If you don't already have a micro:bit, it costs about the same as a dedicated clock or sand timer but is smaller and programmable for other purposes.

The BBC Microbit. The grid of LEDs is in the middle. The A and B buttons are on the left and right.

Here's the code I wrote:

# Pomodoro timer for micro:bit - by Sean McManus - www.sean.co.uk

from microbit import *
import time

display.scroll('Pomodoro')
display.show(Image.HEART)

while True:
    if button_a.is_pressed():
        display.clear()
        for y in range(0,5):
            for x in range(0,5):
                for brightness in range(0,10):
                    display.set_pixel(x,y,brightness)
                    time.sleep(6)
        while not button_b.is_pressed():
            display.clear()
            time.sleep(0.5)
            display.show(Image.HEART)
            time.sleep(0.5)


When the micro:bit powers on, it displays the word "Pomodoro" on the LEDs. It's a useful reminder to me of what program I've loaded onto the device if I come back to it later. It then displays a heart. When you press the A button, the heart disappears and the timer begins. Working from left to right and top to bottom, the lights illuminate in turn. There are 10 brightness levels, so every six seconds the current light notches up its brightness, fading gradually in to full brightness. When the time runs out, the heart image flashes on and off to get your attention until you press the B button. If you get the new v2 micro:bit, it has a speaker built in so you could add an alarm, but I've found the flashing in the corner of my eye is enough to tell me time's up.

I leave the micro:bit plugged into my PC on a USB cable so it switches on when I turn the PC on. You could use it with a battery pack.

Here are four things I learned on this small project:

1. It's surprisingly intuitive to read this clock. When I glance at it, I can easily tell how much time has elapsed. If I see three complete rows and three lights, I can quickly read that as 18 minutes, for example, without needing to add up the lights.
2. It's worth going for a simple solution. At first, I thought about using Python timers and keeping track of which lights had been lit until I realised the solution could be much simpler. It's just three nested loops, progressively making each light brighter. Under the time management technique, you're not supposed to pause a session, but you can abandon one if necessary. I considered adding a cancel button to stop the pomodoro session, but the reset button on the back of the micro:bit does a perfect job of this already. Keep it simple.
3. The clock isn't quite accurate. Code always takes time to run, but I was nevertheless surprised that the difference was noticeable. Over 25 minutes, it runs about 12 seconds slow. I think that's because the operations to illuminate the LEDs are expensive in terms of compute time, and there are 250 LED instructions over 25 minutes. It might also just be the speed the microbit runs at generally. It is an incredible little device, but it is still a low-powered computer. Possibly using a timer driven approach (rather than a delay-based one) would solve this, but for the sake of 12 seconds, I'm happy with this simple solution.
4. When the code's not working, check it's uploaded correctly. I spent some time trying to work out why the timings were wrong, although I'd updated the accelerated prototype to use real time. It turned out the current version had not loaded onto the micro:bit successfully.

If you want to create your own Pomodoro timer, you can paste the code above into the Python editor for the micro:bit, modify it as you wish, and then download it as a .hex file to go on the micro:bit.

Image credit: Bonneval Sebastien via Unsplash. Thank you, Bonneval!

Permanent link for this post | Blog Home | Website Home | Email feedback

Dip into the blog archive

June 2005 | September 2005 | January 2006 | March 2006 | April 2006 | May 2006 | June 2006 | July 2006 | August 2006 | September 2006 | October 2006 | November 2006 | December 2006 | February 2007 | March 2007 | April 2007 | May 2007 | June 2007 | July 2007 | August 2007 | September 2007 | October 2007 | November 2007 | December 2007 | January 2008 | February 2008 | March 2008 | April 2008 | May 2008 | June 2008 | July 2008 | August 2008 | September 2008 | October 2008 | November 2008 | December 2008 | January 2009 | February 2009 | March 2009 | April 2009 | May 2009 | June 2009 | July 2009 | August 2009 | September 2009 | October 2009 | November 2009 | December 2009 | January 2010 | February 2010 | March 2010 | April 2010 | May 2010 | June 2010 | August 2010 | September 2010 | October 2010 | November 2010 | December 2010 | March 2011 | April 2011 | May 2011 | June 2011 | July 2011 | August 2011 | September 2011 | October 2011 | November 2011 | December 2011 | January 2012 | February 2012 | March 2012 | June 2012 | July 2012 | August 2012 | September 2012 | October 2012 | December 2012 | January 2013 | February 2013 | March 2013 | April 2013 | June 2013 | July 2013 | August 2013 | September 2013 | October 2013 | November 2013 | December 2013 | January 2014 | February 2014 | March 2014 | April 2014 | May 2014 | June 2014 | July 2014 | August 2014 | September 2014 | October 2014 | November 2014 | December 2014 | January 2015 | February 2015 | March 2015 | April 2015 | May 2015 | June 2015 | September 2015 | October 2015 | December 2015 | January 2016 | February 2016 | March 2016 | May 2016 | July 2016 | August 2016 | September 2016 | October 2016 | November 2016 | December 2016 | January 2017 | July 2017 | August 2017 | October 2017 | November 2017 | January 2018 | February 2018 | August 2018 | October 2018 | November 2018 | December 2018 | January 2019 | March 2019 | June 2019 | August 2019 | September 2019 | October 2019 | January 2020 | February 2020 | March 2020 | April 2020 | May 2020 | June 2020 | September 2020 | October 2020 | December 2020 | January 2021 | February 2021 | May 2021 | June 2021 | October 2021 | November 2021 | December 2021 | January 2022 | February 2022 | March 2022 | May 2022 | July 2022 | August 2022 | September 2022 | December 2022 | March 2023 | April 2023 | May 2023 | June 2023 | October 2023 | November 2023 | January 2024 | February 2024 | May 2024 | June 2024 | July 2024 | September 2024 | October 2024 | November 2024 | December 2024 | Top of this page |