Here’s a DMD connected to an Arduino with a little laser pointer trip wire.
When the laser beam is cut the timer starts. When the laser beam is cut again it records a “split”. After 6 splits it will stop the timer and start again.
When the arduino boots it gives you 10 seconds to calibrate the laser beam (ie: cut it with your finger a few times). This way the arduino will records the min/max values of the light sensor in the current lighting conditions so that it will know when the beam is cut or not.
When the timer cracks over to 10 minutes + it will hide the micro seconds and just snow minutes/seconds.
Picture of the laser beam cut.
I didn’t get time to fire up the server side PHP logging code. The code records when the timer starts and each time the split is made and shows it on a central website. Multiple of these timer units can be connected to the internet and they will all show up on this central website as different timers.
Here’s the code: https://github.com/dtbaker/arduino-laser-timer