Arduino laser stopwatch - UPDATE

Since in my previous post I was thinking about making PCBs and a new prototype I did exactly that.

I used the toner transfer method to etch my own circuit boards. I don’t have an electronics background so until now I never used any software to draw circuits. But this one (especially the one for the display) was complicated enough that drawing by hand made no sense. The other positive side effect is, that now I have designs that are reproducible. Using hydrochloric acid and hydrogen peroxide to etch the copper was also quite fun:) The results are not perfect, but they work:

After etching the main task was to drill the holes and to solder the vias(connections between the two sides of the PCB). After that soldering everything in place was easy. The components I used are more or less the same as in the first/second prototype.

As seen on the picture above the display has a funky looking battery. That is actually a 18650 li-ion battery. The display is the one part of the system that uses the most power so it makes some sense to make it rechargeable. One can buy really cheap microUSB chargers for those batteries. At 3000+mAh they also pack quite a bit of energy. Unfortunately the 3-4V this battery produces are not enough to drive the arduino(6+V for unregulated supply) and the display(8+V). To get the 8V I needed a step-up voltage converter and again ebay and china had a cheep solution. A full battery is capable of driving the display for up to 4 hours. But since during usage it often turns of(inactivity) we get multiple trainings from one charge. For the trip sensors I decided to leave the 6 AA batteries per sensor. The power consumption on those devices is really low and for me the complexity of adding the charger was not worth it. To determine when the batteries are running low I added a red LED diode that turns on if that is the case. For now this has not occurred:D

The third prototype now looks like this.

As you can see the reflectors are mounted on nicer looking tripods that I got here. The legs are aluminum so it was easy to cut them to a more suitable length.

Since the stopwatch has to be transported I also constructed a nice little box for that.

Made from cardboard and protected with a layer of duct tape. For now it works quite well :)

Some more shots of the finished prototype:

Please let me know what you think about my project. I will also gladly answer any questions that may arise.

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