The BeatBearing Tangible Rhythm Sequencer

By: Peter Bennett

Be your own DJ in a very colorful way! The BeatBearing Sequencer is an exciting, entertaining and innovative way to rock to your own beat. Move the ballbearings on the transparent grid and you change the beat.
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Lots of musicians use a computer to create beats and sequence mixes, but I wanted something to use with other musicians or in a live performance, plus have a unique and cool look. The idea of the BeatBearing Sequencer was born.

Beat Bearing sequencer

What is the BeatBearing? It's a computer interface overlaid with the grid pattern of metal washers and ball bearings. The plastic transparent case is what transforms the sequencer into its uber-coolness. The system is controlled by an Arduino microcontroller and the screen is an old computer monitor cradled in a milk crate.

BeatBearing Sequencer Demo


Required Tools (not included):
Multimeter
Needle nose pliers
Ruler
Screwdriver
Soldering iron
Solder
Wire cutter/stripper
Computer
Metal file
Vise
Router
Band saw
Drill press

Parts List:
Ribbon cable (2 meters), or two 40-wire IDE cables, one with a connector in the center
Hookup wire insulated, solid core, in three colors
USB cable (1)
Microcontroller board (1)
Multiplexer chips (2) NXP (Philips) HEF4067B
Resistors (32) 10Ω
Breadboard (1)
D-sub connectors (2) Solderable, one with crimpable end (if using IDE cables, three 220 male headers)
Screws (64) must fit holes drilled in the washers and pass through the clear plastic base
Solder tabs (64) One flat end for soldering onto; one end with a hole that should fit the screws
Ball bearings (32)
Washers (32) to fit the ball bearings
CRT monitor (be sure the screen isn't curved!)
Acrylic/plegixglass sheet cut to fit CRT monitor screen
Cardboard (4x10 inches)
Duct tape
Milk crate or some other way to hold the monitor, or construct a simple frame from wood
Poster board cut to the dimensions of the CRT monitor screen
Glue, clear

Step 1: Split/Drill the Washers


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

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

Note: Be sure to file edges – washers will be exposed to fingers! (As an alternative to using washers, you can make ball bearing contact switches more easily out of bent wire, or with screws or metal pins arranged in a triangle or square)

Step 2: Construct the Plexiglass Base

The plexiglass base can be milled or made by hand, or you can glue thin horizontal strips of plastic to elevate the washers and make channels for the wires and spare bearings.

A. Cut the acrylic sheet big enough to cover your CRT screen.

B. Create a 4x8 grid on the sheet with each washer. Drill a hole through the plastic to match the washers' inside diameter. Countersink another straightsided hole for each washer that fits its outer diameter and thickness, so the washers will sit flush with the surface of the plastic.

C. Drill two small holes through the plastic for the two screws for each washer (use drilled washers as a guide, so holes are in the right spots).


Step 3: Prepare for Wiring

A. 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.

B. Cut two 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.

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


Step 4: Wire the Base

A. Cut the ribbon cable into two pieces. 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. If you have 40-wire IDE cable, just use one cable.

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

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

D. 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.

Click for Larger Image


Step 5: Build the Electronics

A. Follow the wire schematic (above).

B. Solder wires about 10cm long to the two solderable D-sub connectors. Use a contrasting color for the ground wires and don't bother with the four 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 one hole.

D. Connect the four ground wires from the D-sub connectors to one 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.

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


F. Plug the two 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).

G. 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.

H. Connect each multiplexer's four address pins (10, 11, 13, and 14) to four 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.

I. Wire each multiplexer's common input/output (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.

J. 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.

Step 6: Assemble the Sequencer Base

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

B. 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.

C. 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.

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

Step 7: Install/Run the Software

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

B. 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.

C. Download and install Processing from www.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.

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

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

F. 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 (www.ntonyx.com/vac), although I haven't tried this.

G. From your laptop's display configuration pane, change the second screen's resolution to 640x480 and position it to the left of the primary screen and lined up at the top.

H. 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!

I. 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!

Tangible User Interfaces

I first encountered tangible user interfaces (TUIs) at the Ars Electronica exhibition in 2003, where I saw James Patten's Audiopad project and Sony CSL's Block Jam. These TUIs, along with others I have since found, inspired me to pursue a Ph.D. to study and develop new musical instruments and influenced my design for the BeatBearing.

The main idea behind TUI design is that the user should be given a physical handle on the digital data. Importantly, this handle should allow the user not only to feel and see the data, but also to grasp and manipulate it. In the case of the BeatBearing, you "read" and manipulate the sequencer through the arrangement of the balls.

Click for Larger Image

One design challenge I've found with TUIs is how to include a visual display. Typical computer game interfaces (and others) have you look at the screen while manipulating a controller elsewhere. Many TUI researchers create more direct connections by projecting an image onto a control surface from above or below. I've tried top-projection with instruments I've designed but found it cumbersome, especially if you want a portable instrument for playing live. My solution for the BeatBearing was to ditch the expensive digital projector and show the visuals from below using a cheaper CRT.

I deliberately designed this project to be a base upon which further tangible interfaces could be developed. I believe it has the potential to do much more than this original version.

Modifications

Each part of the BeatBearing is simple enough to allow for easy modification. Here are some ideas:

• Tweak the processing code to change the graphics. How about showing the name of each sample?
• Add a tempo control in the software or add a dedicated potentiometer to the hardware.
• Build the BeatBearing into a coffee table, wooden cabinet or (my favorite), an old leather briefcase.
• Add extra "sample select" holes to one side of the grid, allowing you to switch between sample banks directly from the board.
• Expand the grid. A 16x4 grid would be large enough to create more serious rhythms.
• Use a flat LCD monitor instead of the bulky CRT — a bit more expensive, but much more portable.
• Write new software. You can use the program provided, but if you want to develop your own firmware, the pseudo-code is:

      1. Set address lines on the multiplexers.
      2. Read analog pins.
      3. Repeat Steps A and B to read all the positions on the grid (cycling from 0000 to 1111).
      4. Send out the values of all grid positions over serial.

• Different software applications are possible; for example, rather than a sequencer, how about a real-time performance instrument?

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