Introduction: Stopwatch for 30 M Running (Arduino)

This project was made for specific purpose in Finnish Baseball coaching and testing juniorplayers speed in 30 m running. This arduino projeckt was also a course project in my studies. The project had some ups and downs, but now, at least, it's working.

I decided to use laser poiners and LDRs because I was familiar with LDRs and how they work. More secure system would have been some kind of photoelectric cell. And that will be the next system how I will improve this stopwatch. LDRs and laser pointers create two separate gates. The first gate starts counting time (when the laser beam is blocked at gate 1) and the second gate calculates the final time(when the laser beam is blocked at gate 2).

Code mainly works well, but somehow it shows me some mysterious times ones it starts counting time. In the end, when the time stops, it shows the right time. So give me some help to solve that problem if you have an idea.

Step 1: Materials

(1x) Arduino UNO + USB wire

(1x) 4x20 LCD i2c

(2x) 10k ohm resistors

(2x) LDR (light dependent resistor)


heat shrink tubes

(2x) laser pointer (Ansmann)

(4x) stands for LDRs and laserpointers (2 gates)

(2x) 3R12 4,5 V Battery

(2x) boxes for laser pointers and batteries

(1x) Box for wireing, arduino UNO and LCD

small piece of circuitboard

Step 2: Setup for Laser Pointer Box

In the fritzing picture LED-picture represents the laserpointer as you can see in the other pictures.

Because there's only pushbutton in the laser, I decided to use choker to press it down so the laser is on all the time.

I also modified the laser power source from three button batteries (1,5V each) to one bigger 3R12 4,5V. And because I don't want to take the battery off when I don't need it, I installed a switch.

Step 3: Setup for Arduino, LCD and LDRs

In the pictures you can see the breadboard setup and testing the project. (What a mess... ;))

In the final assembly I brought LDRs to circuitboard (in the box) with two wires and put the resistors there. That was the easiest way to do it. Otherwise I would have had to make small couplingboxes to the end where the LDRs locates and bring three wires from the distance.

Step 4: LDR Gate

I found perfectly fitting rubber blugs to 20 mm iron tube and fastened LDRs with hot-setting adhesive to those rubber blugs.

Step 5: Wireing and Box Makeing

I bought a plastic box which I modified to my purpouses by cutting holes for wires and LCD.

I left only hole for USB wire to arduino because I use this system always with my laptop to write down the result times (from serial monitor) to excel. So this system gets its power from my laptop.

There is small piece of circuitboard inside the box to gather all the wireings in to one. It is attached to the box with small bolt and nut as all the other parts too.

Step 6: Code

Feel free to modify the code to your needs.

The system was tested indoors so make sure that you check LDR values if you want to use it outdoors in a day light.

And as I mentioned earlier there is these mystery times showing during the time takeing. And I don't have a clue where those come from. But I was happy that it works well and gives me the information I need from the players running 30 m distance.

Thanks for your feedback and interest for this project.