led反向应用

ECE 476 Final Project: LED Sensor

Piano Keyboard

Cristina Guzman (cgg27) and Joe Vulih (jpv23)

Contents

Introduction

High level design

∙ Rationale

∙ Background Math

∙ Logical Structure

∙ Hardware/Software Tradeoffs

∙ Standards

∙ Patents

Program Design

Hardware Design

Results of the design

∙ Speed of Execution

∙ Accuracy

∙ Safety

∙ Interference

∙ Usability

Conclusions

∙ Expectations

∙ Applicable standards

∙ Intellectual property considerations

∙ Ethical considerations

Legal considerations

Appendix A: Commented Code

Appendix B: Overall Schematics

Appendix C: Cost details

Appendix D: Tasks

Appendix E: References

Introduction

Our project utilizes an array of LEDs that work as light sensors to generate a musical tone, simulating a piano keyboard.

The basic idea is to use LEDs as both emitters and sensors. For our project specifically, we used a total of 63 LEDs, 9 for each of the seven natural keys. Only the middle LED served as photodetector when the key was pressed, absorbing light from the other LEDs reflected from the finger. We then used the Karplus-Strong algorithm for sound generation, all programmed in C. The tone was passed through an audio amplifier, and can be listened through headphones or speakers connected to the audio jack.

We chose this project because we wanted to do something with LEDs as sensors, and specifically chose music because of our interest in this matter.

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High level design

∙ Rationale

∙ Background Math

∙ Logical Structure

∙ Hardware/Software Tradeoffs

∙ Standards

∙ Patents

Rationale

The rationale behind this idea consists of usinga diode in a 3 step process, as shown in the following schematic. Each step is approximately 1 millisecond long. The upper pin will starts at Vcc and stay there for one millisecond (step one), and then drop to ground for two milliseconds (step two and three). The lower pin will start at ground for step 1, then rise to Vcc for the length of step two and finally the diode will discharge exponentially due to the hole-electron generation due to the incident light on the LED (8 pin leakages).

For the sound generation we will use the Karplus-Strong algorithm developed in the 80s, which is computationally simple. It is a method of physical modeling a string that simulates the sound of some types of instruments, including the piano. It uses a low pass filter and a delay block, which we will implement in software. A schematic of how it works is shown below.