Wireless Digital Wireless Digital Audio TransmissionAudio Transmission

Senior Design ProjectSenior Design ProjectSummer 2002Summer 2002

E. Donnelly, K. Khan, S. OwenE. Donnelly, K. Khan, S. OwenD. ChoyD. ChoyDr. H. LamDr. H. Lam

The Problem …The Problem …

Veronica has lots of cool music (MP3’s Veronica has lots of cool music (MP3’s and wav’s) stored on computer…and wav’s) stored on computer…

……but Veronica wants to play this but Veronica wants to play this music on her stereo….music on her stereo….

… … the Solutionthe Solution

A wireless “link” that connects A wireless “link” that connects Veronica’s stereo to her computerVeronica’s stereo to her computer

Design: Sending musicDesign: Sending music

1.1. Analog audio connected to Analog audio connected to EncoderEncoder

2.2. EncoderEncoder converts audio converts audio MP3 MP3– MP3 compression saves bandwidthMP3 compression saves bandwidth– MP3’s are digitalMP3’s are digital

3.3. MP3 sent to MP3 sent to TransmitterTransmitter via via UARTUART

Design: Receiving Design: Receiving MusicMusic ReceiverReceiver “picks up” transmitter’s “picks up” transmitter’s

datadata Data sent to UART, converted to Data sent to UART, converted to

10-bit packets10-bit packets DecoderDecoder converts MP3 to analog converts MP3 to analog

audioaudio Audio connected to stereo via RCAAudio connected to stereo via RCA

How it Works (HiW)How it Works (HiW)

Encoder / DecoderEncoder / Decoder

InterfacingInterfacing

Wireless transmissionWireless transmission

HiW: Encoder/DecoderHiW: Encoder/Decoder

Micronas MP3 Encoder/DecoderMicronas MP3 Encoder/Decoder– Built in A/D, D/ABuilt in A/D, D/A– Variable bit rate encodingVariable bit rate encoding– Automatic decodingAutomatic decoding– I2C interfaceI2C interface

Atmel AVR MicrocontrollerAtmel AVR Microcontroller– Built in UARTBuilt in UART– I2C interfaceI2C interface

HiW: InterfacingHiW: Interfacing

I2CI2C– Allowed Atmel to ‘talk’ to MicronasAllowed Atmel to ‘talk’ to Micronas– Registers changedRegisters changed

ControlControl DSP coreDSP core CodecCodec

Parallel I/OParallel I/O– 8 Data lines: Input/Output8 Data lines: Input/Output– 5 handshaking lines5 handshaking lines

HiW: Wireless ‘link’HiW: Wireless ‘link’

Linx Tech’s Transmitter and Linx Tech’s Transmitter and ReceiverReceiver– Acts like a wireActs like a wire– Analog or Digital modeAnalog or Digital mode– Speed up to 56 kbps in Digital ModeSpeed up to 56 kbps in Digital Mode

Surface Mount AdapterSurface Mount Adapter

Micronas Micronas MAS3587FMAS3587F– 0.5mm pitch 0.5mm pitch – 64 pin64 pin– QFPQFP– 1.2 cm1.2 cm22

Surface mount Surface mount adapter: Purchasedadapter: Purchased

QFP to PCBQFP to PCB Ironwood ElectronicsIronwood Electronics Pros:Pros:

– Tinned padsTinned pads– Easy to solderEasy to solder

Cons:Cons:– Cost $40Cost $40– 2 weeks to ship2 weeks to ship– Very difficult to debugVery difficult to debug

Surface mount Surface mount adapter: Designed in adapter: Designed in lablab QFP to std. headersQFP to std. headers Designed in ProtelDesigned in Protel Milled in labMilled in lab ProsPros

– Cost $0Cost $0– Easy to debugEasy to debug

ConsCons– Req. solder pasteReq. solder paste– Steady hands, Steady hands,

patience, & good patience, & good visionvision

Our AdapterOur Adapter

The EncoderThe Encoder

SchematicSchematic

Circuit BoardCircuit Board

Encoder Protel Encoder Protel SchematicSchematic

Adapter

Atmel

Programmer

Power Region

RCA JacksDC Blocking and Filter Capacitors

Encoder BoardEncoder Board

Micronas

Atmel

Power Region

DC blocking and filter capacitors

RCA input and output jacks

Atmel programmer headers

6 MHz osc.

18.432 MHz crystal

The DecoderThe Decoder

SchematicSchematic

Circuit BoardCircuit Board

Decoder Protel Decoder Protel SchematicSchematic

Micronas

Atmel

Programmer

Power Region

RCA JacksDC Blocking and Filter Capacitors

Filtered/Unfiltered jumpers

Low Pass Filters

Decoder BoardDecoder Board

Atmel

MicronasDC blocking and filter capacitors

Power Region

Low pass filters

SoftwareSoftware

Micronas initialization Micronas initialization – Atmel sets registers via IAtmel sets registers via I22C C – Developed for communication btwn Developed for communication btwn

ICsICs 2-wire Master-Slave interface2-wire Master-Slave interface

– Data LineData Line– Clock LineClock Line

Original Library functions developed to Original Library functions developed to suit our needssuit our needs

Bus Timing and Bus Timing and ProtocolProtocol

Data I/OData I/O

EncodingEncoding– Parallel Interface from MicronasParallel Interface from Micronas– Atmel passes data bytes to UARTAtmel passes data bytes to UART– UART sends serial data to wireless UART sends serial data to wireless

transmittertransmitter DecodingDecoding

– UART receives serial data from UART receives serial data from wireless receiverwireless receiver

– Atmel gets data bytes from UARTAtmel gets data bytes from UART– Parallel Interface to MicronasParallel Interface to Micronas

SummarySummary

Due to limitations in wireless Due to limitations in wireless transmission bandwidth, a less than CD transmission bandwidth, a less than CD quality sampling rate was used.quality sampling rate was used.

With slightly more bandwidth in the With slightly more bandwidth in the wireless channel(128kbps), CD-quality wireless channel(128kbps), CD-quality sound could be achieved using MPEG 1 sound could be achieved using MPEG 1 Layer 3.Layer 3.

A more expensive wireless portion would A more expensive wireless portion would also solve this problem, and allow an also solve this problem, and allow an uncompressed digital audio stream to be uncompressed digital audio stream to be transmitted.transmitted.