The BeatBearing Tangible Rhythm Sequencer

I had these washers split and drilled by a milling machine at Queens University Belfast’s friendly engineering department, but you can achieve similar results using a band saw and a drill press as follows. Alternatively, you can bypass the washers altogether and make ball-bearing contact switches more easily out of bent wire, or with screws or metal pins arranged in a triangle or square. See the files section for sketches.

Clamp and drill the washers in a drill press, centering the 2 small holes on opposite sides of each.

Use a band saw to cut each washer in half, perpendicular to the axis formed by the 2 holes. It’s easier if you clamp or screw the washer to a jig of scrap metal or wood.

File off any sharp edges. The washers will be exposed to fingers when installed on the instrument.

Like the washers, the base can be CNC-milled or made by hand. Mine was milled; I sent a CAD file to the QUB engineering department to manufacture (see the plan in the files section). You can also drill and rout the base as described here, or else bypass the machining entirely by gluing thin horizontal strips of plastic to elevate the washers and make channels for the wires and spare bearings.

Cut the transparent acrylic sheet to just cover your CRT screen.

For each washer, following a regular 4×8 grid, drill a hole through the plastic sheet to match the washer’s inside diameter.

Countersink another straight-sided hole for each washer that fits its outer diameter and thickness, so the washers will sit flush with the surface of the plastic.

Drill 2 more holes through the plastic for each washer, positioned to align with its screw holes.

On the underside of the base, cut straight channels about 5mm deep running horizontally through each row of holes for the wires. If you’re drilling by hand, use a router along a straightedge fence.

Cut 2 more horizontal channels on the topside of the base, along the top and bottom. These channels will house balls that aren’t currently in use.

Attach the washer halves to the transparent base using screws, holding 1 solder tab above each nut on the underside.

Cut the ribbon cable in 2. With each half, carefully peel the red wire along one side away from the rest of the cable, separating it down to a length matching the grid’s width. These will be the ground wires. With 40-wire IDE cable, just use 1 cable.

One side of each washer connects to ground, so run the ground wires from the ribbons down 2 of the rows, soldering each wire to the tabs on all washer halves facing the same way. For the other 2 rows, cut some spare wire and solder it to the remaining ground tabs and to the ground wire.

For each row, peel away and solder 8 more ribbon wires to the other washer halves, trimming them progressively shorter. Each ribbon will have 3 wire connections unused.

Crimp a D-sub connector onto the other ends of each ribbon, lining them up so that the teeth engage properly with the wires inside. These connectors let you disconnect the grid base from the rest of the electronics.

For all wiring, follow the Wire Schematic Diagram in the photo.

Solder wires about 10cm long to the 2 solderable D-sub connectors. Use a contrasting color for the ground wires, and don’t bother with the 4 unused pins.

With IDE cables, you don’t need to solder. Plug the 3-connector cable’s center connector and one end connector on opposite sides of the breadboard trench, offset by 1 hole.

Connect the 4 ground wires from the D-sub connectors to 1 edge of the solderless breadboard, establishing a ground rail. Use another wire to connect this rail to the Arduino’s ground terminal. To hold the breadboard next to the Arduino, I taped both to a piece of cardboard.

Connect the 5V line of the Arduino to the breadboard along the opposite side from the ground, creating a 5V rail.

Plug the 2 multiplexer chips across the breadboard’s central trench and connect them up to the switch wires from the D-sub connectors. With HEF4067B chips, the 16 independent inputs Y0–Y15 run from pin 2 to pin 9 on one side and from pin 16 to pin 23 on the other.

Don’t worry about the order; comments in the software explain how to sequence the washer inputs there, which is easier than untangling and continuity-testing all the wires.

Connect each multiplexer’s 4 address pins (pins 10, 11, 13, and 14) to 4 of the Arduino’s digital input/output pins. These let the Arduino select which multiplexer input to receive as analog input. Here again, you can designate the sequence later in the software.

Wire each multiplexer’s common input/output Z (pin 1) to one of the analog inputs on the Arduino, A0–A1. Using the analog inputs lets you select the threshold voltage at which the switch is triggered in the firmware. You could use the digital inputs instead for greater speed, but you’d lose the ability to change the threshold.

Connect a 10kΩ pull-up resistor from each multiplexer input up to the 5V rail. This ties all the inputs to the 5V line and prevents them from having a floating signal. When a ball bearing is placed on a washer, the circuit is closed and the input voltage is pulled down to ground.

Lay the monitor on its back in the milk crate, or anything else that will cradle it and keep it stable.

Place the transparent base on top of the screen, and attach the electronics using the D-sub connectors. I taped the electronics to the side of the crate to keep them off the floor.

Size and cut a frame of black poster board to disguise the CRT screen and hide the ribbon cables. (An ideal solution would be to build the screen into a table or cabinet.)

Connect your laptop to the monitor, and to the Arduino via USB cable.

Download and install the Arduino programming environment from http://arduino.cc and the BeatBearing project bundle here. Launch the programming environment. Copy and paste the BeatBearing Arduino code into a new Arduino document, then save.

Select Arduino Diecimilia from the Tools ⇒ Board menu, then click File ⇒ Upload to I/O Board. A message should appear in the comments pane at the bottom confirming that the board was successfully programmed.

Download and install Processing from http://processing.org. The BeatBearing software was created in version 135; it should work fine with the latest version, but if you have problems, switch to version 135.

Download and install the ProMIDI library for Processing from http://texone.org/promidi and the trial version of Ableton Live or Live LE from http://ableton.com.

From Processing, open the BeatBearing Processing program, included in the project bundle. This application reads the position of the balls, then creates the MIDI messages and visuals.

Launch Ableton Live (or another MIDI program or soft-synth) to generate the sound output. The free trial version of Live won’t let you save settings, but you don’t need this to run BeatBearing. On a Mac, configure the program to receive MIDI from Processing via the built-in IAC bus (inter-application communication). With Windows you should be able to route the MIDI using Virtual Audio Cable (http://ntonyx.com/vac.htm), although I haven’t tried this.

From your laptop’s display configuration pane, change the second screen’s resolution to 640×480, and position it to the left of the primary screen and lined up at the top.

Run the Processing program. No error messages should appear, and the monitor should turn black with an array of gray dots and a sweeping red line. If the monitor turns gray, then Processing might not be connecting to the board. In this case, check that all other Processing applications (shown as applets in the dock) are closed and then re-plug the board in and try again!

The Beatbearing Processing code may need some tweaking to get things right, such as lining up the virtual grid with the real grid. The code has been commented to make modifications as easy as possible — the only limit is your imagination!