An interface board was developed to provide 3 ports of 6 discretes and +5V in a 2x5 header connector. It also allows high side switching of the +5V supply. The first version is described here. I did not properly check the power-on state of the enable gpios. I also realized that I should have buffered all of the pins. Most digital IOs have ESD protection diodes. What this means is if you are not careful, a digital high voltage can partially power the part when the main supply is switched off. This has the negative effect of raising a pin above VDD (which is ~0) and can damage the part. The software worked around this by ensuring that when the supply was disabled all IO pins were at 0. I took the opportunity to correct this and add a FET buffer between the BBB gpios and the connector pins.