Control two LEDs with a single Arduino digital pin
This is a special case of Charlieplexing as presented on the YouTube channel learnelectronics in the video titled "How to Charlieplex LEDs with an Arduino". Video link here: https://youtu.be/-4iDWSiCS0s. What I present here is a use case wherein a pair of LEDs each indicate a particular state of processing. In this case READ and WRITE by a TCP client. Since both are mutually exclusive, I reasoned that I could save myself a pin by attaching one LED (RED for read) to Vcc oriented one way and the other (GREEN for write) to ground oriented the other. This allows a single pin to indicate each and when in tri-state, high impedeance (INPUT) mode to indicate neither. The accompanying schematic shows hoe this hooks up to an Arduino UNO.
NOTE: The schematic shows the digital pins but NOT the placement on the board. Use a board layout schematic for that. I used digital pin 12 but any digital pin should work.