A possible project for RetroChallenge: to adapt an old set (or pair) of dictaphone footpedals to work as a volume-control for a SPARCstation.
Difficulty Rating: possible, with a following wind.
Such a device would be marginally useful for playing DOOM and Quake (hands-free volume-control!). It will not really be useful for listening to my song collection, because that activity doesn’t need to be hands-free, but what the heck!
The basic idea would be to hook the switches in the pedals to the modem control-lines (DSR, CTS, DCD) of an RS-232 connector, and route power to the switches from the incoming DTR line. The final piece would be a C program to monitor the SPARCstation serial-port and programatically adjust the master audio-volume as needed (this will require the program to be written as a state-machine with interval-timer so that a press-and-hold causes continuous increase/decrease of volume whereas a press-and-release just changes volume by one step).
In principle, this device would also be usable on those Irix and AIX machines equipped with a serial-port (their serial-port APIs provide explicit access to the RS-232 control signals). An O/S-specific control program would be needed.
Powering the switches from DTR (asserted by the host computer when the program runs) is what appears to be an easy method of avoiding requiring external power supply or batteries, but the implied DC current fan-out might prevent it from working. Fingers crossed!