You already know the input/output cabability of the Voja4 badge is constrained. But is there enough hardware and simulated-4-bit-CPU hardware to enable I2C or even SPI communication? We are going to find out!

Some GPIO-based discrete hardware solutions:

• Two transistors, double NOT, to create open collector mode.
• Is there a better way to make use of the discrete INPUT/OUTPUT signals for I2C?

^^^ This is looking like the right solution. Koppany has a proof-of-concept running on a breadboard, driven by a Pico W. Next step is to port the code to Voja4. I'm working on a schematic/board update that I should be able to get before Supercon. I hope!!!

UART or GPIO to I2C MASTER/HOST:

• Program an 8-pin MCU to be the bridge controller.

UART to I2C MASTER/HOST:

• Is this viable? https://ncd.io/blog/serial-to-i2c-conversion/

I2C [slave] to UART:

Is there a dedicated chip that does the job? Perhaps using a tiny 8-pin MCU is an option.

• The Chip https://www.digikey.com/en/products/detail/nxp-usa-inc/SC16IS750IBS-128/948939
• Retired Sparkfun Breakout https://www.sparkfun.com/products/retired/9981
• Available Breakout https://www.aliexpress.us/item/3256805667898276.html