I'm a swimmer and would like to create a small object that would help me folow my trainning plannification.

In other words I want to create a custum stopwatch, with 5 colored led that will be on or off according to the trainning program.

This is my training:

  • 0:00 to 5:00 : Low Effort (Green light)
  • 5:00 to 15:00 : Medium Effort (Yellow light)
  • 15:00 to 20:00 : High Effort (Orange Light)
  • 20:00 to 25:00 : Medium Effort (Yellow light)
  • 25:00 to 26:00 : Maximum Effort (Red light)
  • 26:00 to 30:00 : Low Effort (Green light)
  • 30:00 Trainning done (Should turn off automaticaly.)

The whole thing must be waterproof. Must work on battery.

I'm asking for some guidelines, I'm not asking for a complete patent(would be appreciated though) but the main idea how to do it. So I can avoid wasting my time on research and tests.

I don't want to spend too much time on the project less than 100 hours maybe. I have studied in computer science and I have most of the materials I'll need. I can buy what is missing.

I'm a little bit noob on this kind of project, I want to know how you do it.

Thanks for help.

  • $\begingroup$ Hi Mark! I voted to close this question ass off-topic, because it's not about robotics, and it's too broad. Please specify what are your main problems? Is it making the watch waterproof, or measuring time, or something completely different? $\endgroup$
    – mactro
    Commented Sep 7, 2016 at 13:09
  • $\begingroup$ (Retracted my close vote as I notice this may be a robotics question after all). Are you wanting this craft to actively follow (or lead?) the swimmer around the pool, or keep station just outside the lane? (I think it's a very ambitious project by the way.) $\endgroup$
    – Andy
    Commented Sep 7, 2016 at 14:10
  • 1
    $\begingroup$ @Andy I think just outside the lane would be a first goal and then I will be able to modify it or make another one with more possibilities, on the wirst for instance. $\endgroup$
    – Mark
    Commented Sep 7, 2016 at 15:04
  • $\begingroup$ @mactro I'm a little bit noob on this kind of project, I want to know how you do it. $\endgroup$
    – Mark
    Commented Sep 7, 2016 at 15:05
  • $\begingroup$ @Mark Ok, this indeed may be a robotic question. Still it is very broad. Try to answer yourself following questions: what propulsion do I need (if any)? How to make it waterproof? How to power it? How to make it measure time? How should it be started and configured? There is a watch for swimmers - kickstarter.com/projects/swimmo/… Maybe you can take some ideas from that? $\endgroup$
    – mactro
    Commented Sep 7, 2016 at 15:56

2 Answers 2


That should be doable and is not that hard. I suggest a small arduino (e.g. Adafruit Trinket), an (RGB LED), a small coin cell and a button. The coding is trivial. You attach this components to a replacement watchstrap so that you can wear it on the wrist. You can activate the system with the button and show your lights. Making it watertight is not that easy, I'd start with transparent heat shrink tube after fixing everything in epoxy. The battery should last some time, replacing it will be a bit tricky.

Update: You could even get rid of the button if you let two metal parts stick out so that they are connected electrically by the water.

  • $\begingroup$ That's the kind of anwser I was looking for. Thx $\endgroup$
    – Mark
    Commented Sep 7, 2016 at 17:03

First things first. If You are studying computer science, learning embedded programming will not be waste of your time. Actually, if you are interested in mobile projects like this, I recommend you to buy ATMega microcontroller with programmer and some electronics, or STM32 Nucleo board.

About your question, I'd create a small PCB with ATMega88 in QFN package, rather than using Arduino, an RTC clock (like DS1307) and communicate them via I2C.

Two buttons would be nice - one for training start/stop, second for display (diodes won't be turned on constantly, only after pushing second button for ~5 seconds - energy saving).

Also, You could use small 7-segment display instead diodes. All these electronics powered by small, ~70mAh LiPo battery, induction charged. And closed in waterproof watch casing.

Moreover, having two buttons and display mentioned above, you could change your training profile without device disassembly.

Yeah. That would be great for swimmers personal training.

  • $\begingroup$ Great, I've already bought a small Adafruit Trinket though. I'll buy the micro usb cable today. I'm thinking about 2 Cmos 3v battery with electric tape for power. I'll consider your suggestion. $\endgroup$
    – Mark
    Commented Sep 13, 2016 at 12:10

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