Raspberry Pi SPI and I2C Tutorial - SparkFun Learn
How to Create a Bidirectional I2C to SPI Bridge - EEWeb
SPI vs I2C Protocol Differences and Things to Consider - Saleae Articles
Adafruit FT232H Breakout - General Purpose USB to GPIO, SPI, I2C [USB C & Stemma QT] : ID 2264 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits
microcontroller - I2C & SPI Operating at the same time - Electrical Engineering Stack Exchange