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Full text of "Musical Instruments"

The BeatBearing Tangible Rhythm Sequencer 



Make] Projects 

hhiiilH ho/ 1 !/ tuMaal/ chare r\icf*f\\tat* 



build, hack, tweak, share, discover,- 



The BeatBearing Tangible 
Rhythm Sequencer 



Written By: Peter Bennett 



f TOOLS: 

Band saw (1) 

Drill press (1) 

to match the screw size, in my case 

2mm 

Glued) 

instead of the ruler and straightedge. 

Same type of plastic as the 15mm sheet 

above. 

Metal file (1) 

ling machine (1) 



PARTS: 



replaces the 5 tools preceding if you 
have access to a friendly engineering 
department 

Multimeter (1) 

for checking connections 

Needlenose pliers (1) 

Router (1) 



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• Ribbon cabled) 
about 2 meters long, or two 40- wire IDE 
cables, one with a connector in the 
center. 

Hookup wire (1) 

to help differentiate ground, power, and 

signal lines 

Ball bearings (32) 

Mine were 20mm. Use chrome-plated, or 

they will rust. 

USB cabled) 

microcontroller board (1) 

It's available from makershed.com. The 

new Duemilanove board should also 

work. 

• Washers (32) 
to comfortably seat ball bearings: mine 
were 30mm outer diameter (OP). 17mm 

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The BeatBearing Tangible Rhythm Sequencer 

• Huier en 

• Screwdriver (1) 

• Soldering iron (1) 

• Vised) 
Wire cutter/stripper (1) 



inner diameter (ID). 

Multiplexer chips (2) 

resistors (32) 

Breadboard (1) 

D-sub connectors (2) 
Make sure they fit together, that one has 
solderable pins, and that the other can 
crimp a ribbon cable. If you're using IDE 
cables, you'll need three 2x20 male 
headers to fit. 

Computer (1) 

The project software is written both in 

Processing and on the Arduino, so it's 

cross-platform. 

CRT monitor (1) 

You can get one cheap or even free 

these days. Make sure the screen isn't 

curved! 

Acrylic/plegixglass sheet (1) 
cut to the dimensions of the CRT 
monitor screen. I used 15mm thick. 

Screws (64) 

Size the screws so they fit through small 
holes drilled in the washers and pass 
through the clear plastic sheet: I used 
M2 (2mm diameter). 

Solder tabs (64) 

One end is a flat tab for soldering onto; 

the other has a hole that should fit the 

screws. 



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• Cardboard (1) 
around 1 0cm x 25cm 

• Duct tape (1) 
Milk crate (1) 

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Page 2 of 13 



The BeatBearing Tangible Rhythm Sequencer 



or some other way to hold the monitor 
horizontal. Improvise, or construct a 
simple frame from wood. 

Poster board (1) 

cut to the dimensions of the CRT 

monitor screen 



SUMMARY 

The BeatBearing is an exciting and intuitive way to make music. Move the balls on a grid, 
and you change the beat. Music sequencing couldn't be simpler. 

Like countless other musicians, I use a computer to create beats and sequence them into 
mixes. Pointing and clicking with a mouse is fine for a studio, but what about when you want 
to sequence rhythms in live performance? Or collaborate with others on a shared rhythm? 
These questions led me to develop the BeatBearing sequencer. 

So what is the BeatBearing? Simply put, it's a computer interface that takes the pattern of 
ball bearings placed on a grid and translates it into a rhythm. The fun part is that the whole 
interface is transparent and sits on top of a computer screen, allowing graphics to be shown 
from directly underneath. The screen highlights which beats are switched on, and what 
sounds they're playing, as a red line sweeps across the screen to show the current time 
position. The system is controlled by an Arduino microcontroller, and the screen is an old 
computer monitor cradled in a milk crate. 



© Make Projects www.makeprojects.com Page 3 of 1 3 



The BeatBearing Tangible Rhythm Sequencer 



Step 1 — Split the washers. 




• 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. 



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Page 4 of 13 



The BeatBearing Tangible Rhythm Sequencer 



Step 2 — Construct the transparent base. 




• 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 4x8 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. 



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Page 5 of 13 



The BeatBearing Tangible Rhythm Sequencer 



Step 3 




• 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. 



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Page 6 of 13 



The BeatBearing Tangible Rhythm Sequencer 



Step 4 — Wire the base. 





• 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. 



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The BeatBearing Tangible Rhythm Sequencer 



Step 5 — Build 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. 







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The BeatBearing Tangible Rhythm Sequencer 



Step 6 




• 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 10kQ 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. 



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Page 9 of 13 



The BeatBearing Tangible Rhythm Sequencer 



Step 7 — Assemble the hardware. 




• 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. 



Step 8 




• 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. 



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Page 10 of 13 



The BeatBearing Tangible Rhythm Sequencer 



Step 9 — Install the software. 

• 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 . 



© Make Projects www.makeprojects.com Page 11 of 1 3 



The BeatBearing Tangible Rhythm Sequencer 



Step 10 






• 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 I AC 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 
640x480, 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! 



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. 

© Make Projects www.makeprojects.com Page 1 2 of 1 3 



The BeatBearing Tangible Rhythm Sequencer 



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. 

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:Set address 
lines on the multiplexers. Read analog pins. Repeat Steps a and b to read all the positions on the grid (cycling from 0000 to 
1111 ).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? 

Resources 

Peter Bennett's home page with BeatBearing news: www.sarc.qub.ac. uk/~pbennett 
This project first appeared in MAKE Volume 17 . page 120. 

This document was last generated on 201 2-1 1 -03 04:24:00 AM. 



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