file under ‘so glad this worked first time, because if it hadn’t i wouldn’t have known where to start’.

as alluded to in the last mixer dev post, the ethernet jack wasn’t just an ethernet jack any more. my first pcb design had the ethernet jack as a ‘magjack’, which has the electrical isolation to protect the circuit from rogue cabling within the jack and was simply a case of leading the signals from the mbed to the jack. however, all the magjacks i could find could not in the end fit within the final tolerances of pcb position and case height, so i had to move to using a discrete isolation chip and a low-profile RJ45 socket. and at that point, the now plain RJ45 socket was suitable for direct connection of DMX - there’s a standard RJ45 pin mapping as well as the XLR type normally seen. so version two of the pcb, in addition to the physical fit issues, had two subcircuits for ethernet and RS485 leading to the socket, carefully electrically isolated and switched.

however, the assember did a snafu and a wrong part was fitted to power the RS485 subcircuit, and it blew on my attaching power. the advantage of it being a subcircuit is that it didn’t take anything down with it, so with an otherwise operational board, the DMX side was sidelined. some months later now the reworking has finally been done, so i made up some RJ45-XLR DMX patch cables, linked in a contributed DMX library from the mbed repository, worked it into the controller’s code, borrowed some DMX gateway hardware… and it just worked! fabulous.