Quick recap.
About power
Circuit must be — Closed
PLUS must connect to GND/MINUS
Power flows only — One way
From the PLUS to the MINUS
About Arduino
1 — Arduino is — Stupid
Only performs the lines we write to it
2 — In Arduino we — Choose pins
A pin can be input or output
Pins, power-wise
Output pin is like — Plus 5V
Output can send power
Input pin is like — NOT GND
Input can read, according to its range
We measure on — A point on a CLOSED circuit
The input measurement is NOT GND
The 3 pin groups are
1 — Digital
2 — Analog
3 — Power
Digital subclass is — PWM — marked with: ~
Ranges are
Digital range is — HIGH / LOW
Analog range is — 0–1023
PWM range is — 0–255
Measuring
We measure things on a — Closed circuit
Input sensor is not ground. It’s a point on the circuit.