Wireless Digital Audio Transmission Senior Design Project Summer 2002 E. Donnelly, K. Khan, S. Owen D. Choy Dr. H. Lam

The Problem … Veronica has lots of cool music (MP3’s and wav’s) stored on computer… Veronica has lots of cool music (MP3’s and wav’s) stored on computer… …but Veronica wants to play this music on her stereo…. …but Veronica wants to play this music on her stereo….

… the Solution A wireless “link” that connects Veronica’s stereo to her computer A wireless “link” that connects Veronica’s stereo to her computer

Design: Sending music 1. Analog audio connected to Encoder 2. Encoder converts audio  MP3 –MP3 compression saves bandwidth –MP3’s are digital 3. MP3 sent to Transmitter via UART

Design: Receiving Music Receiver “picks up” transmitter’s data Receiver “picks up” transmitter’s data Data sent to UART, converted to 10- bit packets Data sent to UART, converted to 10- bit packets Decoder converts MP3 to analog audio Decoder converts MP3 to analog audio Audio connected to stereo via RCA Audio connected to stereo via RCA

How it Works (HiW) Encoder / Decoder Encoder / Decoder Interfacing Interfacing Wireless transmission Wireless transmission

HiW: Encoder/Decoder Micronas MP3 Encoder/Decoder Micronas MP3 Encoder/Decoder –Built in A/D, D/A –Variable bit rate encoding –Automatic decoding –I2C interface Atmel AVR Microcontroller Atmel AVR Microcontroller –Built in UART –I2C interface

HiW: Interfacing I2C I2C –Allowed Atmel to ‘talk’ to Micronas –Registers changed Control Control DSP core DSP core Codec Codec Parallel I/O Parallel I/O –8 Data lines: Input/Output –5 handshaking lines

HiW: Wireless ‘link’ Linx Tech’s Transmitter and Receiver Linx Tech’s Transmitter and Receiver –Acts like a wire –Analog or Digital mode –Speed up to 56 kbps in Digital Mode

Surface Mount Adapter Micronas MAS3587F Micronas MAS3587F –0.5mm pitch –64 pin –QFP –1.2 cm 2

Surface mount adapter: Purchased QFP to PCB QFP to PCB Ironwood Electronics Ironwood Electronics Pros: Pros: –Tinned pads –Easy to solder Cons: Cons: –Cost $40 –2 weeks to ship –Very difficult to debug

Surface mount adapter: Designed in lab QFP to std. headers QFP to std. headers Designed in Protel Designed in Protel Milled in lab Milled in lab Pros Pros –Cost $0 –Easy to debug Cons Cons –Req. solder paste –Steady hands, patience, & good vision

Our Adapter

The Encoder Schematic Schematic Circuit Board Circuit Board

Encoder Protel Schematic Adapter Atmel Programmer Power Region RCA Jacks DC Blocking and Filter Capacitors

Encoder Board Micronas Atmel Power Region DC blocking and filter capacitors RCA input and output jacks Atmel programmer headers 6 MHz osc MHz crystal

The Decoder Schematic Schematic Circuit Board Circuit Board

Decoder Protel Schematic Micronas Atmel Programmer Power Region RCA Jacks DC Blocking and Filter Capacitors Filtered/Unfiltered jumpers Low Pass Filters

Decoder Board Atmel Micronas DC blocking and filter capacitors Power Region Low pass filters

Software Micronas initialization Micronas initialization –Atmel sets registers via I 2 C –Developed for communication btwn ICs 2-wire Master-Slave interface 2-wire Master-Slave interface –Data Line –Clock Line Original Library functions developed to suit our needs Original Library functions developed to suit our needs

Bus Timing and Protocol

Data I/O Encoding Encoding –Parallel Interface from Micronas –Atmel passes data bytes to UART –UART sends serial data to wireless transmitter Decoding Decoding –UART receives serial data from wireless receiver –Atmel gets data bytes from UART –Parallel Interface to Micronas

Summary Due to limitations in wireless transmission bandwidth, a less than CD quality sampling rate was used. Due to limitations in wireless transmission bandwidth, a less than CD quality sampling rate was used. With slightly more bandwidth in the wireless channel(128kbps), CD-quality sound could be achieved using MPEG 1 Layer 3. With slightly more bandwidth in the wireless channel(128kbps), CD-quality sound could be achieved using MPEG 1 Layer 3. A more expensive wireless portion would also solve this problem, and allow an uncompressed digital audio stream to be transmitted. A more expensive wireless portion would also solve this problem, and allow an uncompressed digital audio stream to be transmitted.