Project Number: P13364 (Piano Touch Pad II)

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1 ABSTRACT Multidisciplinary Senior Design Conference Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York Project Number: P13364 (Piano Touch Pad II) Alex Coleman (Elec. E) Bruce Kynoch (Elec. E) Ed Mackowiak (Comp. E) Whitney Zack (Comp. E) Up until now, keyboardists have been faced with a problem when trying to add effects to their music in real time, they only have two hands; one hand for playing the notes and one hand to control the effect being added. The objective of this project was allow the keyboardist to add effects in real time while keeping both hands on the keyboard's keys. A similar project to this was done by Andrew McPherson.[1] This project is an attempt to improve upon the concept by making it more affordable and customizable for the end user. Another aim for this project was to provide a deeper level of control and a broader functionality. This was accomplished by making the keys themselves touch sensitive through the use of capacitive technology and microprocessors. The keys are designed to give the user X and Y position as well as intensity of touch. This gives multiple parameters of control and is individual to each key's PCB. The data collected from the keys is then sent to a software package on a computer through USB to make the sound modifications desired. The sound modifications are done by Plogue, a third party software that allows for sound modification through the entire midi specification. The octave prototype constructed demonstrates full functionality to the project specifications. NOMENCLATURE MIDI Musical Instrument Digital Interface MIDI is a technical standard that defines a communications protocol and set of connectors to allow the act of playing an instrument to be encoded into a digital data stream. For a piano, when a note is played, a packet is sent out from the keyboard that contains information about the event, including the velocity of the keystroke and the pitch 1 of 7

2 of the note. In this project, MIDI is also used to encode X/Y data from touch pads. Software on a laptop is used to read this MIDI signals and generate sound from them. I 2 C Inter Integrated Circuit I 2 C is a particular two wire interface protocol used for chip to chip communication. In I 2 C, one device is the master; all communication on the bus flows through it. The other devices connected to the bus are slaves; the master can read or write data to the slaves. For the master to read data from a slave, the master first sends out the address of the slave it wants to read from, then a bit to signify that it wants to read, not write. The slave then transmits its data back onto the bus. MSP430 Texas Instruments Microcontroller This 16 bit microcontroller is cheap, power efficient, and easy to use, due to its popularity and the large amount of existing documentation. In this project, the chip was programmed using TI Code Composer. Once programmed, the MSP430 can retain its programming after being shut off, so that the keys will be functioning as soon as they receive power. INTRODUCTION introduction PROCESS Using the Project Readiness Package a set of customer needs was determined and from that the specifications were derived. In the specifications sheet timing, budget, interface, tactile feel, accuracy, and number of axes were documented. The specifications for our project can be found in Table (#). Once a clear set of specifications was made, concepts were made to fit within these specs. Some of our concepts met the specifications better than others and through the process of a two stage concept selection the concepts that fit best were chosen. Some of the concepts considered can be seen in Figures (# #). Spec. # Importance Source Function Specification Unit of Measure Marginal Value Ideal Value S1 9 C2, C3 timing Time between finger movement and change in sound S2 3 C8 price The production cost needs to be within budget S3 9 C4 axis white key must sense on two different axis's S4 9 C4 axis black key must sense on two different axis's ms 12 7 USD $150 $100 axis's 2 3 axis's 1 2 S5 9 implie d accuracy finger must be sensed within 5 mm mm of 7

3 S6 3 C7 do not add effect when player does not intend to add it mm 5 S7 9 implie d Interface use a musical interface standard MIDI S8 3 C1, C5, C6 tactile feel no place on key surface should have a change in height mm 2mm 0mm S9 3 C1, C5, C6 tactile feel key overlay should fit on top of key mm 4mm / +0mm 0mm / +0mm S10 3 C1, C5, C6 tactile feel Table (#) Specifications Document key overlay should be in contact with the actual key mm 2mm 0mm Figure # Input Sensor Concept Selection Iteration 1 Figure # Input Sensor Concept Selection Iteration 2 3 of 7

4 Figure # Touch Processor Selection Iteration 1 Figure # Touch Processor Concept Selection Iteration 2 Figure # Supervisor Microprocessor Concept Selection Using the concepts selected it was then possible to create a system architecture diagram. This system diagram did not change throughout the project and it accurately describes the proof of concept demo that was created. The system architecture can be seen in Figure #. The fundamental concept behind the system architecture was capturing the touch sensor 4 of 7

5 information on the key, and then sending that information over a communication protocol to a processor that could communicate directly with the sound generator. To gather the touch data, first, electrodes had to be printed onto a PCB. The sensors (electrodes) themselves are nothing more than copper under a layer of solder mask. The solder mask acts a dielectric, thus creating a capacitor between the copper and a human finger. These electrodes are then connected to the touch processor. On the touch processor the varying capacitance levels are collected for each electrode. This is done trying to oscillate the voltage on the electrode. When a finger is present the capacitance will rise, which increases the time it takes to fully charge the electrode. The oscillator will only start to decrease the voltage on the electrode once it has reached the max voltage. There is no set oscillation frequency for the electrode. This means that the more capacitance there is on the electrode, the fewer times the system will oscillate over a set amount of time. This is how the MSP430 calculates capacitance. Once this data has been collected the location of the finger is found on the X and Y axes. The algorithm to find the location relies on finding the electrode on the axis that has the highest capacitance above the baseline capacitance. Setting this electrode as the starting location, it uses the two surrounding electrodes to find the offset and add that to the location. The location data is then stored in a buffer accessible to the I 2 C interrupt routine. At any point in time, if the supervisor processor requests the location data from a key, they touch processor will pause and respond with the data loaded into that buffer. The supervisor processor is responsible for polling the individual MSP430s on each key to find their X and Y finger location. Once that data has been acquired it is immediately sent over MIDI to Plogue, the sound generation software. Within Plogue, the keyboard data and the touch data is combined to create the sound with the effect applied to it. Figure # System Arcitecture RESULTS AND DISCUSSION 5 of 7

6 The results of the project were largely positive, and have confirmed the validity of the initial premise and project planning. Most of the requirements in the specification were met, with several small exceptions. Starting with the first customer need (CN1), the system meets the specification, since the touch sensitive printed circuit boards added to the keys do not interfere with a pianists ability to play the instrument. Similarly, CN2 was successfully met, as the keyboard feeds its MIDI stream directly to the computer for processing in the Plogue Bidule software suite, which translates the MIDI data into audible sound with minimal delay. CN3 was partially met. Due to a small amount of jitter appearing in the touch sensor data, and time constraints preventing extensive debugging, a finite impulse response filter was added, with the end result of averaging the last 50 milliseconds worth of data to produce a smooth result. The project meets and exceeds CN4. The specification requires two axis control (X and Y) on the white piano keys, and only one axis (Y) on the black piano keys. The project implements both X and Y axis control on both black and white piano keys. The project also meets the requirements for CN5, as the materials added to the keyboard itself do not interfere with the playability of the device. Each printed circuit board added to the piano keys is of minimal thickness, and provides a playing surface with a similar friction characteristics as that of the piano keys before any modifications were performed. Since the entire playing surface of the key was fitted with useable touch sensitive circuitry, there is no need to indicate to the player where the sensor is located, satisfying CN6. Customer Need #7 was partially met. The currently implemented touch modulation scheme uses absolute position of the finger on the key to apply an effect to the key. This is in contrast with relative positioning, which applies an effect based on the difference of the current position of the fingertip, as compared to where the finger first pressed they key, in the context of a single touch of the key. The firmware on the keyboard does not feature a dead zone (so as to maximize the dynamic range of the absolute position data), however a deadzone has been implemented and tested for absolute positioning. Additionally, relative positioning (with a dead zone feature) is a reasonably trivial improvement that could be made to the device with minimal effort. The only specification that was not at least partially met was CN8. The device currently costs an estimated $174 to produce, as compared to the specified $100. More work is needed to further reduce the cost. Some money could be saved by replacing the mbed microcontroller with a less expensive device. Additionally, the printed circuit boards become cheaper when larger volumes are produced. Customer needs 9 and 10 were met. The device is small enough to fit within the footprint of a standard MIDI keyboard, and has been demonstrated to work in a live setting. Overall, the project was a success. Over the course of MSD I and II, the project was conceived, planned, implemented and tested. As previously stated, a majority of the customer needs were met or exceeded. CONCLUSIONS AND RECOMMENDATIONS 6 of 7

7 conclusions REFERENCES [1] A. McPherson and Y. Kim. Design and applications of a multi-touch musical keyboard. Proc. Sound and Music Computing, Padova, Italy, PDF ACKNOWLEDGEMENTS Gerry Garavuso Faculty Guide and Customer Dr. Patru Engineering Advice Don Slepian Keyboard Advice & Keyboard Dr. Becker Gomez Engineering Advice & mbed 7 of 7