Visual programming with a real Arduino (4/4): mini-controller

A mini-controller is a program that reads an input, decides, and produces an output, repeating in the loop. Choose one of these two base challenges (they use
the built-in LED, no wiring):

In this project, Arduino run first is for preparation that only happens once.
The main part (read input, decide, and act) goes inside Arduino loop forever
because the controller must keep checking the input.

- Threshold indicator: read a potentiometer; if it passes a threshold, the LED
stays steady on; otherwise, the LED blinks slowly.
- Two-mode alert: read a button; if pressed, the LED blinks fast; otherwise,
it blinks slowly.

*Optional extensions (only if your teacher confirms the hardware): use external
LEDs for a traffic light, or a servo motor for two positions. These are not
required.*

Fill the table before you build. Use only one row for your base design and
leave the extra rows empty. In that row, write which input you will read, what
decision or threshold the program will use, which output you will observe, and
how you will know it works.

Build a small first version. Do not try to make it perfect at first. It must
include: one input reading, one if / else decision, one observable output, and a
wait if the behavior repeats too quickly.

Example of the "Threshold indicator" challenge (steady on above the threshold,
slow blink below):

Arduino loop forever:
   if  [read analog pin# [A0]]  [≥]  [threshold]
   do:
      [set built-in LED] [HIGH]        # above the threshold: steady on
   else:
      # below the threshold: slow blink
      [set built-in LED] [HIGH]
      [wait] 400 milliseconds
      [set built-in LED] [LOW]
      [wait] 400 milliseconds

Choose one small improvement and apply it:

- Adjust the threshold so it switches where you want.
- Change a wait time so the blink is easier to see.
- Use a repeat N times block to avoid copying blocks.
- Make the two modes easier to tell apart.