Thanks that's great, would you power off the 5v or 3.3v rail? I am creating another stage after this of UL2803 to control some relays.
Out of interest, like the 595s are the MCPs prone to errors? For example with the help of Mario I used a stage to buffer the output of the 595s for long enough to reload the chip in case of errors, without affecting the output.
Many thanks
Andy