A magnet is taped to the underside of the tank car.
The track has 8 reed switches attached underneath. As the train drives by the magnet activates the reed switch and it sends the output of the keyboard to 3 banks of 8 switches. (dip switches.. plan on replacing these with toggles eventually.) The first bank of 8 switches connect to 8 different bends that vary in pitch and sound different depending on which keyboard voice is selected. The other 2 banks are 2 more bends but you can kind of "program" the rhythm of how they're triggered based on how the 8 switches are flipped. Combining bends at the same step in the sequence can cause unpredicted chaos/aleatoric glitches/harsh noise madness. The humbuckers on each side of the track pick up the sound of the dc motor as it passes. The instrument has 1x 1/4" output for the keyboard audio , 1x 1/4" output for each humbucker, and 1x rca video out for CRT visuals. Everything runs into my big box of circuit bent weirdness and some effects. Created for a performance at Circuit Benders Ball 2021.