Wireless Null Modem

1
Wireless Null Modem

• Infrared Palm Pilot Communication Device

2
Team Members

• Team Leader
• Peter Trenkle
• Group Members
• Huiyang Sim
• Shaun McFarland
• Stephen Porter

3
Abstract

• Design an infrared console that eliminates the
  need for a DB-9 serial cable to transmit data to
  a PDA
• Develop software that will allow users to
  establish a data link between the console and the
  PDA
• Supply a cheap, convenient alternative to a
  laptop interfacing to an ASCII display menu

4
Diagram of Hardware
PIC Controls capture of serial data from SPI Port
and UART. This data is then decoded from/encoded
into IrDA compatible data
From RS-232 _at_ 19.2 kbps
MAX3100
To PALM
Maxim 3100 Controls IrDA Timing for the PIC
Infrared Transceiver
From PALM
5
Design Constraints

• Design an Infrared Console to Establish a Data
  Link and Tx/Rx RS-232 data through the Infrared
  Data Link
• Transmit and Receive Infrared Data at a Rate of
  19.2kbps

6
Design Constraints (Cont.)

• Develop Software for PALM to Display ASCII Menus
  and Serial Data
• Create a 1 meter Infrared Data Link
• Power Entire Console with one 9V battery

7
Low Power Requirement

• A new IR Xceiver allows for control of Duty Cycle
  and Current-Limiting Resistance
• Duty Cycle and Current-Limiting Resistor can
  affect battery life
• Due to the excessive power needed by the IR
  transceiver, several aspects of the transmitted
  data are observed
• screen refresh rates
• amount of characters on each screen

8
Embedded Software Design

• Used the PCs serial port to transmit serial data
  to verify the PICs onboard UART
• Create Modular I/O routines for SPI module on PIC
• Interface the PIC to the Max3100 UART to control
  IrDA timing
• Transmit and Receive Data between the RS-232
  Interface and the Infrared Interface

9
Palm OS Software Design

• Learned the CodeWarrior language for Palm OS
• Started with Hello World program
• Worked with Initial Serial Port programs
• Program created that allows for bi-directional
  serial communication
• Sends Data Bi-directionally from PC to Palm Pilot
• User Input Functionality must be added
• Changed serial port program to interface to the
  Palms onboard infrared port

10
Unforeseen Design Problems

• Unconnected Ground Planes between Console and PC
  caused strange results
• Intermittent Problems with CodeWarrior
  development system for PALM
• Small Footprint of IR Xceiver is extremely
  difficult to interface to
• Pin 4 (Receive) and Pin 8 (Gnd) are presently
  shorted together

11
Test Specification

• Oscilloscope
• Checked the clocking of the SPI Port of the PIC
  and the Data Rate of the RS-232 Interface
• Allowed for complete verification of hardware
  design
• Logic Analyzer
• To test the actual movement of bits
• Will allow for trigger on Chip Select to actually
  observe operation
• Low Power Testing in a real-world environment

12
Low Power Testing

• Power Testing and Verification takes 2 PHASES
• Continuous Use (PIC constantly xmitting)
• Typical Use (PIC periodically xmitting)
• _at_ Different Baud Rates, Determine Time Until
  Battery Exhausted
• Find Best Baud Rate Best Resistance
• IR Xceiver can be put in SHDN mode between
  xmissions and still receive data
• Following Formula will be used to determine power
  draw
• Battery life in hours 120mAh / X ( mA drawn)

13
What We Promised

• Demonstrate our bi-directional Palm Pilot
  terminal program
• Any IR Links unable to be implemented would be
  simulated by a null modem cable
• Transmit/Receive IR Data with limited IrDA
  functionality
• PC Board would be laid out

14
Where We Are

• IR Communication using Palm Pilot
• Current Range Nearly 1 foot
• Range Angle Maximum 30 degrees
• Basic Serial Communication using PIC
• Interfacing to UART thru SPI port
• PC Board is laid out and ready for order

15
PCB Layout
16
Where We Stand
Hardware Design
Determination of Components
Finished Schematic
Palm OS Dev.
PIC C Firmware Dev.
Hello World On Palm
Basic Serial I/O into the PIC
Serial Com Via Palm
Packetize Data
Infrared Com Via Palm
Final Testing and System Integration
17
Whats Left.

• VT100 functionality for the Palm Pilot
• Make I/O more efficient
• Interrupt driven
• Get rid of Polled Input
• Address Power Concerns and nail down a battery
  life value when the product is robust
• Second order of parts

18
Summary

• IR console will soon be ready for packaging
• Palm Pilot program that displays ASCII data on
  screen is working
• Bi-Directional Communication is kind-of working
• A convenient, low-cost alternative to null modem
  communications will soon exist!

19
Acknowledgements

• We would like to thank Dr. Robert Reese, our
  advisor, for all his patience and input
• We would also like to acknowledge Dr. Joseph
  Picone for his support

20
References

• 1 "About IrDA Software Protocol,
  http//www.irda.org/standards/standards.asp,
• Infrared Data Association, Walnut Creek,
  California, 1996.
• 2 P. Barker and A. C. Boucouvalas, Effect of
  Random Alignment Sway on the
• Performance of IrDA Handheld Devices,
• http//www.irda.org/design/reference.asp,
  Infrared Data Association, Walnut
• Creek, California, 1996.
• 3 M. Cremer, An Introduction to the IrDA
  Protocols, PDA Developers 2.6,
• pp. 35-39, Nov/Dec, 1994.
• 4 T. Engdahl, "Get Power Out of PC RS-232
  port,
• http//www.epanorama.net/circuits/rspower.html,
  Epanorama.net Electronic
• Circuit Design, August 25, 2001.
• 5 L. Goldberg, Infrared Data Transmission The
  Missing Link? Electronic
• Design, pp. 47-64, April 17, 1995.

21
References

• 6 "IrCOMM Serial and Parallel Port Emulation
  over IR (Wire Replacement),
• http//www.irda.org/standards/standards.asp,
  Infrared Data Association, Walnut
• Creek, California, 1995.
• 7 "IrDA Data Link Design Guide,"
  http//www.hp.com/go/ir, Hewlett Packard, Palo
• Alto, California, 2000.
• 8 C. Knutson, Infrared Data Communications
  with IrDA, presented at IrDA
• Conference, 1998.
• 9 P. Langley, Leading Alternative for Serial
  Ports IRDA, Electronic
• Engineering Times, p. 54, August 17, 1998.
• 10 P. Megowan, IrDA Infrared Communications
  An Overview,
• http//www.irda.org/design/reference.asp,
  Infrared Data Association, Walnut
• Creek, California, 1996.
• 11 T. Salazar, UART test mode provides clock
  for RS-232-to-IrDA translator,
• Electronic Design, pp. 124-125, February 21,
  2000.
• 12 "Serial Infrared Link Access Protocol
  (IrLAP) Version 1.1,
• http//www.irda.org/standards/standards.asp,
  Infrared Data Association, Walnut
• Creek, California, 1996.