I have a ton of ideas and I love to imagine new things that can be practical or be a new challenge for myself. I have invented quite a few things, some of which were silly or too complicated to do, others were interesting and doable but never made it out of my desk drawer, some just failed, some were interesting and useful and I still use them today... Well you get my point, I imagine and try to create a lot of things. The first goal is mainly to learn something and have fun along the way, but also to solve a personal challenge that I might have.

The Idea

In early 2020, many countries were locked down due to the Covid. Gym have also closed. A lot of people had to do their training at home, including me. Having a timer is especially handy if you are doing HIIT exercises. I was using my phone as a timer but it never came in handy, it is always on standby, you always get a notification from every apps and you can break it.

Source: https://www.roguefitness.com/rogue-echo-gym-timer

Proof Of Concept

The best way to start something when you have an idea is to start small.

In other words, try to make a fairly early version with what you have in your lab.

In my case, I had an Arduino and some electronic parts that I got from an old box to start electronics. The first step I did was create a basic timer that works with an Arduino and a seven segment display. I coded a simple POC with a breadboard.

POC timer


Before going any further, I decided to try to sketch out what I had in mind. The sketch below shows you the kind of things I imagined.

First sketch
Second Sketch

Hardware & Code

With the new 7 segments received and a pretty good idea of ​​what I wanted, I started to code all the programs and make the connection between the components. The link to the Github project will be added at the end of the article.

New 7 segment
  • Tabata training — Interval (30 sec / 10 sec)
  • EMOM — Interval (every minute)
  • Pomodoro timer — Time management method
  • Arduino Nano for the final prototype
  • A piezzo buzzer
  • 4 buttons for selection
  • A power button with LED
  • An old power bank
  • Magnets
Power bank connection
Power button

3D Modeling the Case

Once I had all the code and hardware ready I designed the case on Fusion 360. I own a 3D printer so I did some testing before I found the perfect setting.

First 3D printed case
Sketch of the inside
3D Printed case
Final Sketch


After finding the right setting for the case, it was time to put everything in place. The first step was to glue the magnets and finish the welding.

Magnets Assembly
Final Assembly

Final Prototype

After all of this process, it was time to close the case. The images below show the final prototype.

Final Prototype
Final Prototype
Final Prototype
Final Prototype Working

What next?

I wanted to take it a step further and see how much it can cost to have a marketable end product. So I contacted a company specializing in this type of prototype. The price was over 4000 euros just for the design of the PCB.


The whole process was really interesting, it took me over 2 weeks to have this final prototype (minus the delivery time for each part). It was interesting to think about the design of the object but also to do the various tests. Along the way, I had some failures and had to 3D print about 7 cases.

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