This question came from figuring out how to drive an SPI chip over a few meters distance. Normally, you’re not supposed to do that: I2C and SPI in particular are designed for use on a PCB, i.e. distances in the order of dozens of centimeters at best. Fortunately, in this case speed was not an issue, so what if we simply take the clock signal way down, to say 10 KHz (50 µs on + 50 µs off). Can we create a solid SPI setup across a few meters of wiring?