Self-Playing Xylophone

Matt McKinney, Electrical Engineering

Project Advisor: Dr. Tony Richardson

April 1, 2018

Evansville, Indiana

Acknowledgements

I would like to thank Jeff Cron, Dr. Howe, and Dr. Richardson for helping me through

the senior project process.

Table of Contents

I. Introduction

II. Background and Problem Definition

A. Background

B. Problem Statement

III. Design Approach

A. Design process

B. Software Design

C. Hardware Design

D. Mechanical Design

E. Parts List

F. Standards and Constraints

G. Costs

IV. Results

V. Conclusions and Recommendations

A. Recommendations

B. Conclusions

Appendix A

Appendix B

Appendix C

References

List of Figures

1. Picture of Xylophone

2. Software Flowchart

3. SD Card Circuit

4. Key Striking Circuit

5. Solenoid Mechanical Layout

6. Final Project

List of Tables

1. Table of Costs

I. Introduction

Many engineers struggle with the concept of music and many musicians struggle with the

concepts of engineering. Music and engineering are simply two very different subjects. This

project, a self-playing xylophone, blends these two unlike subjects. This is done by using

engineering principles to create music. To do this first a microcontroller reads in a song. Next

the microcontroller uses pin manipulation as an input to supporting circuitry. Finally this

circuitry controls solenoids which strike xylophone keys to play a song. The final result plays a

song. This project is useful for STEM education purposes. It could be taken into a school and

used as a demonstration piece to excite kids about the possibilities of engineering.

II. Background and Problem Statement

A. Background

Before addressing how to play a xylophone with solenoids, it is important to explain how

humans play xylophones. The musician holds two mallets. The instrument is a collection of keys

that each play a specific note when struck by a mallet [1]. Striking these keys in the right order

plays a song. A xylophone is pictured in Figure 1.

Figure 1: Picture of Xylophone [2]

B. Problem Definition

The minimum specification of the project was to play a simple song. This was done by

using the microcontroller to control 4 solenoids that strike the keys of the xylophone. The

microcontroller had a song preloaded on it. It will directly control 4 pins that were each linked

to a solenoid. The microcontroller used its programming of the song to play the xylophone.

After this was done the project was expanded upon.

After a simple machine capable of playing music was created, the next step was to

improve the system. This was done by adding features and expanding on what was already

completed. The project currently plays 15 keys. A demultiplexing system allows for controlling

more solenoids. A power circuit powers the solenoids. The software also plays more keys and

reads in musical files. The final product is also user accessible both in price and function. This

means that a normal person should be able to use this product and also afford it.

III. Design Approach

A. Design Process

The first task is to read in the song and interpret it. To read in the song it was chosen to

use an SD card. The challenge with this was to access the contents of the SD card with the

microcontroller. This was further complicated when one of the pins for this was already in use as

an output. The problem had to be worked around by rewriting the output code to use different

pins. The first musical file format it was planned to use was MIDI, but MIDI was overly

complicated for this project. So instead, ABC file notation was used. It is not overly complicated,

but still holds all the song information that this project needs. ABC is also easily interpreted as

characters by the microcontroller.

For the output to control the solenoids, the project uses pin manipulation. The challenge

was to pick the correct pins because the microcontroller has a limited number of pins. This

problem became further complicated by the use of an SD card and using serial communication

for debugging. The solenoid activation pins had to be reassigned.

The circuitry must be capable of controlling and powering the solenoids. It is necessary

for the logic circuit to be able to control all of the solenoids given a limited number of

microcontroller pins. This problem was further complicated by the fact that it is not easy to

locate the correct parts. Many of the ideal parts are no longer in production. When powering the

solenoids, it was important to find the right components that could provide the necessary amount

of power, not burn out while providing that power, and also be cost effective.

The solenoids must be able to play the song while also not drawing too much power.

They must also be cost effective.

The mechanical had to be made so that the project could be supported. First a small

prototype was built only using a couple of keys. After that a full design was created and

constructed considering aesthetics, durability, functionality, and cost.

B. Software Design

At the highest level the software reads in a musical file from an SD card. Then it uses the

file information to control I/O pins that play the xylophone keys

The microcontroller establishes communications with the SD card. Next, it opens up the

musical song file. Once the ABC (file overview of ABC file notation in Appendix A) is being

read off the SD card, the next step is to create an output based on the ABC file input. Stepping

through the file line by line, each character is evaluated. First, the header section of the ABC file

is ignored. Next, each note is read in. The code checks where the note is on the scale and how

long it is played. This is done determining if the note is an upper or lower case letter. Then

subtracting based on whether it is upper or lower case. Then it is checked if the note has a

character a certain character after it. If there is, another subtraction is made. Through these two

subtractions, the note in the song is converted into a number which correlates to a position in an

array. The position in the array correlates to the physical key on the xylophone which is to be

played. After determining the note, the next character is checked to see how long the note is to

be played and a delay is set that correlates to how long the note should be played. Finally, to

play the note the physical key to be played is loaded into the I/O pins. The output is quickly

enabled and disabled to strike the key and then there is a delay corresponding to how long the

note is to be played. If the note is within range, the note is played for the desired time. Then the

next note in the song is checked and the process is repeated until the song is over. A flow chart

of the code is given below in Figure 2.

Figure 2: Software Flow Chart

C. Hardware Design

At a high level, the hardware provides power to the project, allows for the SD card to

communicate with the microcontroller, controls and powers solenoids, and provides power to the

project.

The SD card circuit is straightforward with wires running directly between the

microcontroller and SD card reader. The circuit shown below in Figure 3.

Figure 3: SD card circuit

After the music file is interpreted by the microcontroller the next step is to demultiplex

the 5 pins from the microcontroller into a single output. This was done by making a 5 to 32

demultiplexer. This was done by cascading five 3 to 8 demultiplexers. The demultiplexers are

active high because the solenoid retracts when they are turned on. This circuit runs on 5 volts.

After the demultiplexer there is a power circuit which powers the solenoids. This circuit consists

of an NPN transistor which is being used as a switch and a diode snubber. This circuit is

triggered by the 5 volt logic circuit, but provides 12 volts to the solenoid. The circuit is shown

below in Figure 4.

Figure 4: Key striking circuit

The solenoid is used to strike the xylophone key. The solenoid has an electromagnet

which retracts the cylinder when it is turned on and releases the cylinder when it is turned off. To

strike the key the solenoid is quickly turned off and then back on. This is shown below in Figure

5.

Figure 5: Solenoid mechanical layout.

D. Mechanical Design

The goal of the mechanical design is to support the rest of the project. The mechanical

design consists of two parts: the xylophone and the support apparatus. The xylophone was first

altered by cutting off the extra plastic with a Dermal tool. After doing this there was only the

xylophone. Next, polycarbonate was cut and drilled and mounted above the xylophone with a

hole above each key. A solenoid was mounted in each hole so that it can strike its corresponding

key. A polycarbonate sheet was mounted above the unused sharps and flats keys to support all of

the hardware and software electronics. The mechanical design is shown in Figure 6.

E. Parts List

SD Card Module: Used to interface SD card with microcontroller. [3]

UNO R3 Board ATmega328P: Microcontroller used in project. Picked because this

Atmel chipset is well developed, cost effective and the engineer had experience with it.

[4][5]

MM74HCT138N: 3:8 demultiplexer used to link micro output to solenoid power circuit.

Also active high which is required for project. [6]

N2222: NPN transistor used to power solenoids. Cost effective transistor that fits within

the power specifications.

1N4001: Diode used for snubber circuit. Cost effective diode that fits within the power

specifications [7]

3V-12V DC 80mA-350mA Micro solenoid: This solenoid provides enough power to

strike the solenoids with good sound quality and also does not draw too much current. [8]

NOTE: These solenoids did not end up being used because the supplier sent the wrong

solenoids. The solenoids that where shipped are lower power and do not work as well.

#10-24 Screws/nuts: A good size machine screw that is robust enough to support the

project

Polycarbonate: Used for mounting solenoids. Strong enough to support mechanical stress.

Also clear so that project can be viewed.

25 Note Xylophone: Children’s xylophone that can handle the mechanical apparatus

attached to it and also produce reasonable sound quality. [9]

PS-5231-5DF1-LF power supply: The power supply was chosen because provides

necessary voltages.[10]

F. Standards and Constraints

When designing this project it is important to take several factors into account.

Economically/Manufacturability, the design will is able to be produced so that it if it ever

becomes a consumer product it can be manufactured economically. This is done by choosing

parts that are easily mass produced. This means that the parts are manufactured or produced

cheaply. Environmental impacts must also be considered. Solenoids draw a lot of current and

thus power. This power is reduced to decrease the environmental impact. Also, if this product

were mass produced the manufacturing techniques would need to be analyzed for environmental

impact. Social/political/ethical, most people think of music as simple entertainment, but some

people use it for harm. Many songs have been shown to be racist, offensive, and political. This

product will have the capability to play these songs. To do this may be wrong, but since I am not

personally playing the song I will leave that choice up to the individual. Two factors come into

health and safety. If water is spilled on the project it could short out and become a shock hazard.

The final project has taken steps to reduce this risk. Also, the solenoids contain cylinders which

have the potential to come free. These cylinders could then be choked on. The project has tried to

eliminate this threat by making it so the solenoids are unable to come free.

For this project ISO/ICE/IEEE standard 24748-5-2017 [11] was considered. This

standard relates to the life cycle of software. The project has software so the life cycle of said

software is important.

G. Costs

The table of costs is given below in Table 1.

Table 1: Costs

IV. Results

The overall result is a working prototype of a self-playing xylophone. This prototype

could be adapted to go into full scale production. The entire working project has several

working sub parts. Working hardware includes an SD card reader, logic circuit, and key striking

mechanism. The working code sections that read in an ABC file form an SD card, interpret ABC

Product: Quantity: Cost: Part Total:

Microcontroller $1.00 $30.00 $30.00

Solenoids 15 $7.99 $119.85

Demultiplexer 4 $0.59 $2.36

Transistors 15 $0.02 $0.30

Diodes 15 $0.05 $0.75

SD Card Adapter 1 $5.99 $5.99

Polycarbonate Sheet 1 $10.99 $10.99

Hardware 1 $4.99 $4.99

Xylophone 1 $32.55 $32.55

Power Supply 1 $14.99 $14.99

Total $222.77

file notation, and create an output based on the ABC file notation. The project also has a solid

mechanical design. Which could also be adapted to if the project went into production. A picture

of the project is below in Figure 6.

Figure 6: Final project

V. Conclusions and Recommendations

A. Recommendations

If this project were to be remade or put into production, there are several things to be

considered. The solenoids right now are active high instead of active low. This means that to

retract they need to be turned on. The power consumption of this project could be optimized if

they were active low. Before going into production it would be important to get a reliable

solenoid supplier. For this project the solenoids were purchased from an unreliable supplier and

the wrong solenoids were delivered.

B. Conclusions

As stated in the results, this is a working project. It can be used to get kids interested in

STEM. The project could be expanded on to include controlling more keys, playing cords, or

adding a touch screen. There are many different directions that this project could be taken into.

Also, the way that the project is now, it could be taken into production. So to summarize this

project is working as is and can be expanded on or taken into production.

Appendix A

This appendix discusses ABC file notation. The first thing in an ABC file is the header.

It contains information about the song. The header is denoted in Figure 5. The next part of the

file is the notes. The notes correlate to the notes in the song. This is also denoted in Figure 5

below. [12]

Figure 6: ABC file example [12]

Appendix B

This appendix includes the code used on the Self-Playing Xylophone project.

const int enablePin = 9;// Control pins

const int controlPin0 = 2; const int controlPin1 = 3; const int controlPin2 = 5; const int controlPin3 = 6; const int controlPin4 = 7; const int button = 8; char song[] = "C, D, E, F, | G, A, B, C|D E F G|A B c d|e f g a|b c' d' e'|f' g' a' b'"; byte notecontrol[] = {0x01,0x02,0xFE,0xFE,0xFE,0xFE,0x00,0x08,0x09,0x03,0x04,0x05,0x06,0x07,0x0FF,0xFF,0x0A,0x0B,0x0C,0x0D,0x0E,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF};

void setup() { // put your setup code here, to run once: Serial.begin(9600);

pinMode(enablePin, OUTPUT); pinMode(controlPin0, OUTPUT); pinMode(controlPin1, OUTPUT);

pinMode(controlPin2, OUTPUT); pinMode(controlPin3, OUTPUT); pinMode(controlPin4, OUTPUT); pinMode(button, INPUT); digitalWrite(enablePin, LOW); } void loop() { // put your main code here, to run repeatedly: for (int i=0; i < sizeof(song) ; i++){ int note = song[i];

if ((song[i] >= 'A' && song[i] <= 'G')){ note = note - 58; if (song[i+1] == ',') { note = note - 7; } Serial.println(notecontrol[note]); Playnote(notecontrol[note]); } if ((song[i] >= 'a' && song[i] <= 'g')){ note = note - 83;

if (song[i+1] == 39) { note = note + 7;

} Serial.println(notecontrol[note]);

Playnote(notecontrol[note]); } delay(250); } } void Playnote(byte n){ Serial.println("Playing note"); Serial.println(n);

if( (n & 0x01) != 0){ digitalWrite(controlPin0, HIGH); Serial.print("1"); } else{ digitalWrite(controlPin0, LOW); Serial.print("0"); } if( ((n>>1) & 0x01) != 0){ digitalWrite(controlPin1, HIGH); Serial.print("1"); } else{ digitalWrite(controlPin1, LOW);

Serial.print("0"); } if( ((n>>2) & 0x01) != 0){

digitalWrite(controlPin2, HIGH); Serial.print("1"); } else{ digitalWrite(controlPin2, LOW); Serial.print("0"); } if( ((n>>3) & 0x01) != 0){ digitalWrite(controlPin3, HIGH); Serial.print("1");

} else{ digitalWrite(controlPin3, LOW); Serial.print("0"); }

if( ((n>>4) & 0x01) != 0){ digitalWrite(controlPin4, HIGH);

Serial.println("1"); } else{ digitalWrite(controlPin4, LOW); Serial.println("0"); } digitalWrite(enablePin, HIGH); delay(50); digitalWrite(enablePin, LOW);

}

Appendix C

This appendix includes the circuit schematic used on the Self-Playing Xylophone project.

References

[1] ‘How Does a Xylophone Work?’ [Online]. Available: https://ourpastimes.com/how-does-a-

xylophone-work-12165630.html [2] ‘Kids Xylophone’ [Online] Available: www.educationaltoysplanet.com/wood-

xylophone.html [3] ‘SD Card Module Slot Socket Reader for Arudino UNO R3 Mega 2560 Nano’ [Online]

Available:

https://www.amazon.com/gp/product/B00WH7WXRC/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

[4] ‘ARDUINO UNO REV3’ [Online] Available: https://store.arduino.cc/arduino-uno-rev3 [5] ‘AVR 28 Pin 20MHz 32K 6A/D - ATMega328P’ [Online] Available:

https://www.sparkfun.com/products/9061

[6] ‘MM74HCT138N’ [Online] Available: https://www.mouser.com/productdetail/on-semiconductor-fairchild/mm74hct138n?qs=%2FXEtZmhGuCGdB8ctGZq3Og%3D%3D

[7] ‘100x 1N4001 Molded Plastic Case Rectifier Diodes, 1A, 50V DO-41’ [Online] Available: https://www.amazon.com/gp/product/B06XC1V28Z/ref=oh_aui_detailpage_o02_s00?ie=UTF8

&psc=1

[8] ‘3V-12V DC 80mA-350mA Micro solenoid electromagnet push and pull dc Miniture electromagnet Mini Solenoid Electromagnet’ [Online] Available:

https://www.amazon.com/gp/product/B00ZC53KB4/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

[9] ‘Lyons 25-Note Xylophone (Glockenspiel) with Case’ [Online] Available:

https://www.amazon.com/Lyons-25-Note-Xylophone-Glockenspiel-Case/dp/B001VO7FPC/ref=sr_1_1?s=industrial&ie=UTF8&qid=1521143716&sr=8-

1&keywords=25+note+xylophone [10] ‘Server Supply’ [Online] Available:

https://www.serversupply.com/products/part_search/query.asp?q=PS-5231-5DF1-

LF&msclkid=7c383f8a1ccd167ce61c655562d48266 [11] ‘ISO/IEC/IEEE 24748-5:2017’ [Online] Available:

https://www.iso.org/standard/60062.html [12] ‘How to understand abc (the basics)’ [Online] Available:

http://abcnotation.com/blog/2010/01/31/how-to-understand-abc-the-basics/