I'm looking for an ADB device that lets me monitor at least three TTL signals and control one TTL signal. I want to implement a Macintosh program that will handle a number of uninterruptible power supplies (UPSs). The intention is that the program can shut down a Macintosh network gracefully.

Using an ADB device will free a serial port from being dedicated to monitoring a few lines for a change of state. Is there a device able to handle the above TTL signals?

We have not been able to find an ADB-based product that has these abilities. The Apple Desktop Bus is typically used for products such as keyboards, trackballs, mice, and so on, and it isn't likely that someone has worked on something of this nature.