The project is a systems simulation designed for use as a procedures trainer built on the Arduino Mega, using I2C and a broad spectrum of components including a variety of switch types, LED and FET-driven incandescent lights, rotary encoders, servos, SD audio, as well as the components pictured; PCF8574 GPIO breakout boards, and the TCA9548A I2C multiplexer driving multiple 0.91” 128x32 OLEDs.
When a 3rd PCF8574 GPIO breakout board is added, all 0.91 128x32 OLEDs that functioned properly before the addition of the GPIO board, cease to display (dark). All other components in the circuit work as designed, including those attached to the newly added PCF8574.
All I2C addresses are confirmed with a scan and no duplicates present. Error checking confirms all allocations are successful in the sketch including the SSD1306. I2C components are running off of 3.3v.
Libraries utilized in the sketch are as follows: