The example I2C isolation circuit from [Max’s] paper. The SPI implementation is even simpler. [Max Holliday] found himself in this exact situation, running 69 I2C and SPI devices in a single ...

the Raspberry Pi 4 has six SPI controllers, six I2C controllers, and six UARTs – all on its 40-pin header. You can’t make use of all of these at once, but with up to four different connections ...