My kids always brush too fast.
So I make them a clock with a button on the top which when pushed will start counting from 1s to 120s.
They are now using that as their 2 minute timer.
It is a pretty simple project,
if you have an RTC clock and an Arduino compatible board you can get it done.
Step 1: Material
1 Sparkfun Redboard (or any Arduino compatible)
1 Seven Segment Display kit
1 RTC DS1307 Clock kit (see Adafruit Tutorial on how to get or build one your self)
1 push button
Some Plexiglass for overall case. I just make a box from it and glue them together. Nothing fancy.
The RTC Clock is put inside an empty dental floss container so I don't have to cover or worry about short circuiting the board inside the case.
Step 2: Setup your connections
Time to get your breadboard out.
I used Sparkfun tutorial here to connect the 7 segment
I am opting for the Serial UART connection.
Similarly I use this Adafruit tutorial for my RTC clock connection with i2C connection