Blink or steady

A slide switch as a mode selector. Its common pin goes to GPIO27, pin 1 to ground and pin 2 to 3.3 V, so GPIO27 reads low with the lever left (where it starts) and high with it right.

An LED on GPIO17:

• lever left: the LED is steadily on
• lever right: the LED blinks, 0.25 s on, 0.25 s off

Read the switch continuously — it can change at any time. The test slides it right at 2 s and back left at 5 s.