Digital Tuner Project Team Haribo Jen, Mihir, Mike, Sami, and Zack

Overview •  Project Overview •  Hardware Building •  Digital Measurement Chain Implementation •  Digital Signal Processing •  Digital Tuner Microcontroller Programming

Project Overview The Digital Tuner Project consists of: •  Building a Digital Tuner Board •  Sampling and conditioning input signals •  Converting input analog signals to digital •  Processing and analyzing digital signals •  Determining guitar string note and tune •  Relaying sensor data to the user via LEDs

Project Overview

Hardware Building The Digital Tuner Board is constructed from

soldering electronic components, including: •  Atmega1284P microcontroller

o  Runs C code ("Brain" of the board)

•  USB to UART transmitter o  Thing that connects to the computer and sends/

listens for messages

•  Microphone o  Captures input sound signals

Hardware Building Functional components of the Digital Tuner

Board: •  Microphone (input) •  Operational amplifer •  Low-pass filter •  Analog-to-digital converter •  Microcontroller •  LEDs (output) •  USB to UART transmitter (output)

Hardware Building Microcontroller

Microphone LED lights

USB to UART transmitter

Buttons

Digital Measurement Chain The Digital Measurement Chain (DMC)

consists of six stages: •  Signal input •  Signal conditioning •  Anti-aliasing •  Sample & Hold •  Analog to Digital Conversion •  Digital Signal Processing •  Output

DMC Implementation

DMC Implementation Digital Tuner Board hardware already achieves: •  Signal Input (Microphone) •  Signal Conditioning (Op amp) •  Anti-aliasing (Low-pass filter removes

erroneous artifacts from input signal)

DMC Implementation Digital Tuner Board microcontroller accomplishes: •  Signal sampling •  Analog-to-digital conversion

o  Converts analog signal to digital signal

•  Digital signal processing o  Performs transformations and analyzes signal to

determine guitar note and tune

•  Output o  Transmits information to computer over bus line or

blinks LEDs to communicate with the user

DMC Implementation Digital Tuner Board microcontroller accomplishes: •  Signal sampling •  Analog-to-digital conversion

o  Converts analog signal to digital signal

•  Digital signal processing o  Performs transformations and analyzes signal to

determine guitar note and tune

•  Output o  Transmits information to computer over bus line or

blinks LEDs to communicate with the user

Signal Sampling Signal sampling: taking measurement of a

signal at a specified rate and number of sample points

Signal Sampling Goal: reconstruct the original signal as

accurately as possible!

Signal Sampling What happens if we sample too slow?

ALIASING!

DMC Implementation Digital Tuner Board microcontroller accomplishes: •  Signal sampling •  Analog-to-digital conversion

o  Converts analog signal to digital signal

•  Digital signal processing o  Performs transformations and analyzes signal to

determine guitar note and tune

•  Output o  Transmits information to computer over bus line or

blinks LEDs to communicate with the user

Analog to Digital Converter Goal: convert analog signals to digital signals

Analog to Digital Converter Why? Simplified and faster signal processing!

Would you rather work with analog numbers (1.239454..., 8.323423...) or digital numbers? (1, 2, 3, 4, 5, ...)

Drawbacks: Quantization error

DMC Implementation Digital Tuner Board microcontroller accomplishes: •  Signal sampling •  Analog-to-digital conversion

o  Converts analog signal to digital signal

•  Digital signal processing o  Performs transformations and analyzes signal to

determine guitar note and tune

•  Output o  Transmits information to computer over bus line or

blinks LEDs to communicate with the user

Talked about in the

microcontroller coding section!

Where are we?

Digital Signal Processing Goal: Determine which guitar note and tune the

input signal corresponds to How? 1. Convert signal to frequency domain 2. Calculate signal's amplitude spectrum 3. Determine frequency of input signal 4. Match frequency of input signal to known

guitar string frequencies

Digital Signal Processing Goal: Determine which guitar note and tune the

input signal corresponds to How? 1. Convert signal to frequency domain 2. Calculate signal's amplitude spectrum 3. Determine frequency of input signal 4. Match frequency of input signal to known

guitar string frequencies

The Fourier Transform

The Fourier Transform Why? Easier to determine the frequency of the

input signal!

Digital Signal Processing Goal: Determine which guitar note and tune the

input signal corresponds to How? 1. Convert signal to frequency domain 2. Calculate signal's amplitude spectrum 3. Determine frequency of input signal 4. Match frequency of input signal to known

guitar string frequencies

The Amplitude Spectrum

Digital Signal Processing Goal: Determine which guitar note and tune the

input signal corresponds to How? 1. Convert signal to frequency domain 2. Calculate signal's amplitude spectrum 3. Determine frequency of input signal 4. Match frequency of input signal to known

guitar string frequencies

Matching Frequencies Frequency (Hz) Guitar Note

82.41 Low E

110.0 A

146.8 D

196.0 G

246.9 B

329.6 High E

Matching Frequencies In tune? Frequencies falling in between these regions are considered flat or sharp notes Digital Tuner Accuracy?

Due to low precision in the ADC and hardware limitations, frequency calculations are approximate

Frequency (Hz) Guitar Note

82.41 Low E

110.0 A

146.8 D

196.0 G

246.9 B

329.6 High E

Microcontroller Programming

The aforementioned digital signal processing steps all take place in the microcontroller!

C programming!

User Interaction The Digital Tuner Board communicates the guitar

note and accuracy to the user, via LED lights.

Questions?