ECE597 Fall 2014 Project Bonekey Bonekey

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thumb‎ Embedded Linux Class by Mark A. Yoder


Team members: Jiayu Guo, Zizhao Wang

Grading Template

I'm using the following template to grade. Each slot is 10 points. 0 = Missing, 5=OK, 10=Wow!

09 Executive Summary
09 Installation Instructions 
08 User Instructions
08 Highlights
10 Theory of Operation
09 Work Breakdown
10 Future Work
09 Conclusions
10 Demo
10 Not Late
Comments: Nice project.  Thanks for fixing up the wiki.

Score:  92/100

Executive Summary

We got the idea from Makey Makey which is a invention-kit to use everything to be Keyboard. Like banana, water, even cat all can be keyboard. For this project, we created a Bonekey Bonekey to play with sound. Our Bonekey Bonekey uses banana as keyboard to play piano tones. This design is consisted of a main microcontroller, a PCB board, a USB sound card, and an audio player. We use Beaglebone to get the separate input informations and produce corresponding tones to the audio player. One of human's wrist is mounted by reference ground and human can use either figures to touch bananas to produce different tones. Our Bonekey Bonekey will not only use bananas as inputs but also apples, water and everything.

Installation Instructions




The board and the schematic files can be found in the Github repository.

SV1 - Connect to the beagle bone from P8_7 to P8_17.

SV2 - Connect to bananas.

SV3 - middle pin connect to power and the two side pin connect to ground.


Qty Value Parts
7 1M R1, R2, R3, R4, R5, R6, R7
7 2N2222 T1, T2, T3, T4, T5, T6, T7
7 4.7M R8, R9, R10, R11, R12, R13, R14

USB Sound Card

Since the beagle bone doesn't have an audio output we need to add a USB sound card to the bone.

We have tested two USB sound cards



All together



Build CSound from source

Build Csound from source Beaglebone. The BonekeyBonekey need CSound6 but the apt-get version is still CSound5

bone$ sudo apt-get build-dep csound
bone$ sudo apt-get install cmake git
bone$ cd ~
bone$ mkdir csound
bone$ cd csound
bone$ git clone csound
bone$ mkdir cs6make
bone$ cd cs6make
bone$ cmake ../csound
bone$ make -j2
bone$ sudo make install
bone$ sudo ldconfig
bone$ cd cs6make

Clone BonekeyBonekey Repository

 bone$ git clone

Disable HDMI

Follow this link to disable HDMI, and make some GPIO pins available.

Make the USB sound card as the default output

copy the asoundrc file from the Github repository to your home folder.

bone$ cd asoundrc ~/.asoundrc

User Instructions

  1. Follow the installation instruction to make sure you got the hardware and software installed.
  2. Connect SV1 on the PCB borad to beaglebone P8-7, 9, 11, 13, 15, 17.
  3. Wire up seven bananas to the 7 inputs to SV2 of the PCB board.
  4. Connect the USB sound adapter to the beaglebone, and also connect a headphone or speaker.
  5. Run the Bonkey program.
bone$ python

Then you can play the bananas.


Bonekey Bonekey is project that can turn almost every conductors into a music keyboard, such as fruits, water or people.

The idea come from MakeyMakey by Jay Silver in Santa Cruz, CA

Playing Bonekey Bonekey

Please watch our video and have fun.

Theory of Operation

Wow, that's much clearer.  Thanks...



  • First we disabled the internal pull-up resister of the GPIO, because we need a very large pull-up resistor.
  • All the GPIO pins we used have a 4.7MOhm pull up resistor, and connected to a banana.
  • The resister of human skin is about 10K-100KOhm, so when we touch the bananas, the GPIO pins are grounded.

Voltage level

  • The GPIO pins on the beaglebone detect the voltage higher than 2.6V as high, but when we use a 4.7MOhm resistor, the voltage level can not reach 2.6V.
  • We use a 2N2222 general purpose transistor as a switch to make the voltage level reach 2.6V.
Simulation result when grounded
Simulation result when pulled up



The flow chart of the python program.

Python program flow chart


  • Csound has an internal function to generate piano like sounds
  • We just need to set up a Csound instrument and send a frequency message to it.

Piano instrument definition. Documentation for prepiano

instr 1
aa,ab prepiano p7, 3, 10, p4, 3, 0.002, 2, 2, 1, 5000, -0.01, p5, p6, 0, 0.1, 1, 2
outs aa*.2, ab*.2

Initialize score.

f1 0 8 2 1 0.6 10 100 0.001
f2 0 8 2 1 0.7 50 500 1000

Then the python program will send a note to csound dynamically when the GPIO interrupt is activated.

perfThread.InputMessage("i1 0.0 0.5 1 0.9 200 " + freq[0])

Work Breakdown

PCB design

We did PCB design together. We tried to use several values of the pull-up resistor, however there was not low enough voltage value for GPIO reading as 0. Finally we decided to use transistor as a switch to pull down the voltage once the base of transistor connect to ground.

GPIO Read Input

Jiayu did the GPIO read input part in python. The GPIO will read high voltage as 1, and low voltage as 0. And also using javascript to disable internal pull-up and pull-down resistor.

Csound Play Sound

Zizhao did the Csound play part. In python, the .sco and .orc Csound files are created, Csound options are set, and the tones are played by Csound.

Hardware Parts

Zizhao bought the resistors and transistors, Jiayu bought the bananas.

Future Work

  • Use serial port for input so that we can add more input keys and make a real midi device
  • Optimize CPU usage in csound so the BeagleBone can generate more notes at the same time
  • Add some more instrument tones, and use a push button to select them


In this project, we designed a banana midi piano, which is consist of a BeagleBone, a PCB, USB sound card and a audio player. So far we can only play very easy songs with these seven piano notes. In the future, we may add more features, like add more inputs or add different tones to play more songs. As well we may optimize CPU usage to play more notes simultaneously and Coherently.

thumb‎ Embedded Linux Class by Mark A. Yoder