Single RU units such as the SPN16i and SPNConference will give you 15 logic inputs for buttons or 10K linear pots and 8 logic outs for LED"S or contact closure control. The two RU units such as SPN32i, SPN1624, SPN2412 and SPN1612 will give you double that amount (30 in, 16 out). Each logic input can be used for level control (of single or multiple I/O's), to execute macros, call up presets or invoke actions. The macro control language in the ASPEN series is powerful and allows you to build sophisticated control systems with simple, push button interfaces - take a look at the RCWPB8 as an example.

Don't overlook the possibility of using the RS232 port as a control port as well! The send string command in the macro language allows you to build control commands to be sent to other serial controlled devices in your system. With a single button, you can have the ASPEN system change levels, route signals to different speakers, dial the far side connection and lower your projector (and turn it on) - all through a single macro.