Tag Archives: IBM Selectric

20 Questions

My housemates Jodi and Mark are members of Invisible. Mark is co-creator of the Selectric Piano (and the dancer in this video); Jodi is at the keyboards. This description is from Invisible’s MySpace page:

“Here’s a Video of the song 20 Questions, performed earlier this year at 1001 in Greensboro. It features Jodi on the Selectric Piano, an instrument built by Fred Snider and Mark Dixon that interfaces a typewriter with a piano. notes and letters. The video was shot by Jon McLean and edited down by Bart Trotman.”

Tech info on the Selectric Piano:

“To begin with, the IBM Selectric typewriter is a marvel of engineering! The typewriter is 100 percent mechanical and employs a 6 digit binary coding system to direct its type ball to the proper latitude and longitude for each character that the typist types. To access that six digit code we placed tiny light sensing switches at each of six bars that transfer the keystroke to the type ball. The shift command adds another switch and thus a seventh digit to the code. That code is “cleaned up” electronically by circuits we mounted on the typewriter itself. The code is then sent via a printer cable to the piano playing assembly. There we use chips called ‘demultiplexers’ to translate the seven-digit binary code into a base-ten number between 1 and 88. Amazingly, the IBM Selectric types exactly 88 characters — that’s the number of notes a piano plays! That demultiplexed signal is amplified to 33 volts on its way to to contract the appropriate solenoid. Each key has its own dedicated solenoid and ‘finger’ assembly made from our plastic cutting board, some hard maple and brass rods for pivots. The piano-playing assembly sits in front of the piano on a bench. It is not permanently attached to the piano. Jodi applies sustain via a douglas fir two by four which is attached to the piano’s sustain peddle using two bent nails.

“Incidentally, some of the first ‘letter quality’ computer printers were IBM Selectrics that were rigged to computers in the exact opposite way as described above. Solenoids operated the typewriter’s six bars, shift and return functions. This was available as a package conversion but many old school hackers like Fred, one of the makers of the Selectric Piano, made their own at home.”


Filed under movie of the week