E 90 is the analog electronics lab, and it was my first real exposure to serious analog design. I built an infrared wireless audio transmitter/receiver set. You plug a stereo into the transmitter and a pair of headphones into the receiver, and you can walk around listening to your music unencumbered by wires. Well, as long as you are facing the transmitter and don't walk too far away. The sound quality is pretty good, though.