Timers & State Machines

We can’t describe everything in terms of finite states, but that sure hasn’t stopped us from trying.

Outline

• millis() & micros()
• Super loops
• random() & randomSeed()
• structures
• typedefinitions
• switch-cases
• State machines

Exercises

1. Blink two LEDs every 389 and 991 milliseconds.

2. I miss the days of bringing quarters to school for a snack at the vending machine, so let’s make one to bring this childhood memory of mine back to life! Create a simple state machine to turn your Arduino into a vending machine! Your state machine should have the following states:

   • Collecting quarters
   • Item dispensing
   • Returning change (if any)

   Since this is a “proof of concept” device, let’s make the following simplifications:

   • Print status information to the serial console to let the user know what’s going on.
   • Pressing a button adds a quarter.
   • Pressing a button will toggle between items.
   • Pressing a button returns users their change.

   And to complicate things a bit, let’s consider the following:

   • Have at least three different priced items with a finite stock.
   • Add a 30s timeout from the last inserted quarter. On timeout, return all change.
   • Randomly reject quarters at a 1% rate and let users know about this failure.
   • Blink the built-in LED every second so users know the machine is still on.