Three-Floor Elevator Controller

A shop on three floors installs a small goods lift. Staff call it with one button per floor. A naive controller serves calls in the order they were pressed and makes the car shuttle past floors where someone is waiting. This one must work like a real lift: keep going in its direction and stop on the way. Times are shortened for the bench, and this is a programming exercise on an emulated board, not a certified lift controller.

Hardware

• Arduino Nano 33 BLE (nRF52840, 3.3 V logic). Serial console on Serial1 (D0/D1), 115200 baud. Serial is USB and is not seen by the tests.
• Call buttons for floors 1, 2, 3 on D2, D3, D5, each to GND. Use the internal pull-ups (LOW = pressed). A press counts once, after 20 ms without a break, however long the button is held.
• Lift indicator panel (lamps with resistors on board, HIGH = on): floor lamps F1 on D4, F2 on D6, F3 on D8; UP arrow on D9, DOWN arrow on D10; DOOR lamp (door open) on D11.
• The car takes 500 ms to move one floor. The door stays open for 700 ms.

Write the sketch in sketch/sketch.ino. In setup() open Serial1 at 115200 baud, set up the pins and the start-up lamps, then print READY. Never block with delay(): calls can come at any moment.