It was a single IR LED and four sensors as I recall. They had some Sun workstations (used mostly for circuit simulations) in mid-90's at the university where my

It was a single IR LED and four sensors as I recall. They had some Sun workstations (used mostly for circuit simulations) in mid-90's at the university where my mother used to work. I was in the middle school at the time and very interested in anything electronics. Still am. Blue LEDs went mainstream few years later.