HI again, what I need (and telling from the comments from other customers across the web, they need it too) is the circuit diagram of the pHAT board (the Americans call it a schematic). You’ve hinted at the need for this in your reply “The rest is level shifting and protection circuitry…” (typo corrected ;-) - in order to experiment with the board it’s essential that all lines, components, pullups, etc. are understood. For example, what power supply decoupling is on the board; which power pins are used; what are the 6 resistors for that are lined up alongside the module; how does the drive to the firmware LED work and where does it connect to (there’s what looks like a transistor on the board, driving the LED, but that’s guesswork).
So in summary, if you’re supplying a board that’s intended as an experimentation base, it’s essential that the circuit diagram is provided with it (also, a link from the Pimoroni website product page to the link you sent in your first reply would be very helpful).
So please would you supply the circuit diagram (schematic) for the pHAT board.