EE332 Junior ProjectSound Recorder

Spring 2001

Chris Brophy

Matt Olinger

Instructor: S. D. Gutschlag 4/26/01

Block Diagram

•Top Down Design

•Sample input audio

•Store in memory (Emac board)

•Play audio output

Audio Input

• Amplify microphone input

• Shift and Clip to protect A/D converter

• Sample input with software

Microphone PreAmp

• Basic Op-Amp with feedback for simplicity

• Easily adjustable offset for A/D

A/D Clipper Circuit

©2001 Brophy and Olinger

Software

•For sampling, used Timer 0 Interrupt

•For REC/PLAY/STOP buttons, used EXT3,5,6

•For LEDs, used P1.6 and P1.7

Software

Sample Rate

•Adjustable with T0

•Set to 6kHz for human voice

•Maximum necessary frequency is 3kHz

•Double for Nyquist Theorem

•32KB of memory

•Recording time of 5.3 seconds

Square Wave Memory Dump

Sine Wave Memory Dump

Audio Output

•“Unshift” Output of D/A•Amplify•Output on speaker

Audio Output

Preliminary Speaker Amplifier

Audio Output

Final Speaker Amplifier

FFT

Due to sampling effect of A/D,results are similar to the PAM lab.

Aliasing effect is also seen past theNyquist Theory frequency limit.

Conclusions and Performance

Audio Samples

•Test at 3.6kHz Sample Rate

•Test at 5.9kHz Sample Rate

•Test at 16.4kHz Sample Rate

All objectives were achieved:•Microphone input•Record into memory•Output through speaker