The clock counts down to a selectable time, and repeats the countdown every 15 minutes (the normal interval for the metro over here). Three minutes before it is time to leave, the clock display starts flashing slowly to get your attention. Then, once you should have left, the clock counts UP, blinking fast, as you still have time to make it if you walk briskly. Once your time is TRULY up the countdown to the next metro starts.
To save batteries, the clock goes into as low power mode as possible after about an hour, and you have to switch it off and on again to restart it.
The clock is built using an Arduino, and has a battery powered real time clock to remember the time while powered off.
To make it truly stand alone I added the possibility to set the time and time-to-leave using buttons.
The clock was built into a custom made plexiglass box, and the outside covered with a design printed onto photo paper with a sticky back side. I used my wife's Cameo vinyl cutter printer to cut the paper - I just love that machine!
Here are some pictures from the process:
|The Arduino with the RTC module to the right, time-set buttons in the middle and 7 segment display at the bottom.|
|To keep the top and bottom of the case in place while gluing on the sides, I built a little Lego rig. We all use Legos for prototyping, don't we?|
|The finished box|
|Sanded down to make the photo paper stick.|
|Power switch and stand-offs added.|
|Everything fits snuggly. Notice that I kept the USB input to be able to update the software if necessary|
|Voila! The finished product. Now my wife is never late for the metro ever again. Riiight.|