I bought an 8-port general purpose IO expander for adding ports to my MSP430 projects via I2C, but I couldn’t find any library for accessing it. Fortunately the I2C communication with the on-board Texas Instruments PCF8574 chip is pretty straightforward, so after studying the LiquidCrystal_I2C library, which uses the PCF8574 for communicating with the popular 16×2 LCDs, I made my own library for this port expander. You are welcome to it. I release it as Public Domain code.
For my office door I’ve made a sign using a 16×2 LCD display controlled by an MSP430 and connectable via Bluetooth. A button lets me cycle through canned messages like, “The doctor is in,” and “At lunch.” Via Bluetooth I can give it an ad hoc message that I had not pre-programmed.