Wireless PDA Text Messaging

A Full-Duplex Messaging System

between 2 PDAs

Jency Jacob

Talat Ozyagcilar

Outline

Objective Overview Software Hardware Difficulties Questions

Objective

The objective is to equip 2 PDA devices in a way such that users are able to simultaneously send and receive messages between one PDA and another.

Overview

Project Components1. 2 PDA devices

2. 2 FM Transmitters and 2 FM Receivers

3. 4 RF antennas for over-the-air communication

4. Level Shifter for Interfacing RF ICs to the PDA

5. 2 power supplies for the transmitters and receivers

Overview (cont’d)

General Overall System Transmission

Protocol

Overview (cont’d)

General Overall System (cont’d)

Interfacing Palm OS

Overview (cont’d)

Software

User Interface Description Packet Description Encryption/Decryption Test Strategy/Debugger Overall Flow Diagram

Software – User Interface Description

Software – User Interface Description (cont’d)

Software – Packet Description

Header - $FF End of Data - $01 (more data), $00 (done)

Encoding Sequence # - Range 0 - 255 End of Packet - $9F

Packet Sequence # - Range 0 to 6

1st Data - 4 bytes of encoded user message

Checksum - Packet Mid-point

2nd Data - 6 bytes of encoded user message

Software – Packet Description (cont’d)

Header - $F5

Control Indicator - $F1FA (Connection Establishment) , Packet Seq # (ACK)

End of Packet - $9F

Software – Encryption/Decryption

Encoding sequence number Encryption table: Identical static tables containing

random numbers

Encoding: Encoded data = Data + Encoding #

Decoding: Decoded data = Data – Encoding #

Software – Testing/Debugger

Debugger Module Viewing receive buffer

and various error flags Sending/Receiving

single packets

Software – Testing/Debugger (cont’d)

POSE: Palm OS Emulator

Software – Overall Flow Diagram

Software – Overall Flow Diagram (cont’d)

Hardware

Components1. PDA

2. Level Shifter

3. Regulators for Power Step-Down

4. Power Supply (9V battery)

5. Transmitter/Receiver Pair (418mhz, 433mhz)

6. Antennas

Hardware – PDA

Sony Clie PEG-SJ

Series

Hardware – Level Shifter/Regulators/Power Supply

Level Shifter – TTL to CMOS Level Converter

Regulator – Obtaining 3.3V & 5V from 9V Battery

Power Supply – 9V Alkaline Battery

Hardware – FM Transmitter

Hardware – FM Receiver

Hardware – Antennas

Difficulties

Capturing data in dedicated receive buffer Utilizing the processor between handling

events and capturing/processing packets Handling noise introduced to the system

through the transmitter/receiver pair

Questions