Wireless Null Modem

1
Wireless Null Modem

• Infrared Palm Pilot Communication Device

2
Team Members

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

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
Design Constraints

• Design an Infrared Console to Establish a Data
  Link
• Transmit and Receive Infrared Data at a Rate of
  19.2kbps
• PALM Software to Display ASCII Menus and Serial
  Data
• Create a 1 meter Infrared Data Link
• Power Console with 9V battery for 4 hours

5
Major Design Challenge

• Improper Infrared Encoding
• MAX3100 did not encode IR data properly bytes
  lost in long strings
• To fix, an IR encoder is used (TOIM4232)
• To implement the encoder, a radical redesign is
  needed

6
Original Hardware Design
PIC 16F873
RS-232 Line Driver
PIC Controls capture of serial data from SPI Port
and UART. This data is then decoded from/encoded
into IrDA compatible data
On-Board UART
From RS-232 _at_ 19.2 kbps
On-Board SPI Port
Maxim 3100 Controls IrDA Timing for the PIC
To PALM
Infrared Transceiver
MAX3100
From PALM
7
Redesigned Hardware
TOIM4232
RS-232 Line Driver
IR XCVR
To PALM
From RS-232
From PALM
PIC 16F873
To control TOIM4232 mode of operation
Operates at 3.3V, current draw lt 2 mA
8
Advantages of New Console

• Less Power Needed
• The circuit runs at 3.3V, thus decreasing power
  draw
• Parasitic Power may be able to power entire
  console
• Fewer components needed
• Possibly no battery
• Packaging becomes smaller

9
Disadvantages of New Console

• Two components tied to TOIM4232 RS-232 port
• PIC needs port to configure the TOIM4232
• Line Driver connected directly to the RS-232
  ports
• Determine new resistance value that will allow
  for 1 meter IR transmission

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Parasitic Power

• Definition Taking of power from the serial port
  on one of the unused RS-232 pins
• Supply power to Console (1020 mA)
• Feasible if we increase external resistance to IR
  Transceiver
• Pin outs for Voltage Regulator for Battery
  Powered Option

11
Parasitic Power Schematic
12
Schematic

• Transistor vs. Voltage Regulator solution
• 78L05 Voltage Regulator dissipated too much power
  (10 mA)
• Diode and Transistor power base dissipates
  minimal current (.1 2 mA) depending on load
• Decreased Power Dissipation more available
  current
• With Voltage Regulator 3.3V _at_ 5mA
• Transistors 3.3V _at_ 15 mA

13
Parasitic Power Comparison
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The POWER Challenge

• Power aspect of this project deals with the
  console interface to the IR Xcvr
• External Resistance
• TX vs. RX mode
• Power balanced with Range Specification
• Due to the small current draw of the
  encode/decode components, current draw to Xcvr is
  closely monitored
• Old Design Enc/Dec 4mA _at_ 5 V
• New Design Enc/Dec lt2mA _at_ 3.3 V

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IR XCVR Pinout
External Resistance determines majority of
current drawn by circuit
PIC 16F873
IRED
TX
RX
TFDS4500
Vcc1/SD
5V
Ground
16
POWER DATA
1m Specified
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POWER DATA
54mA specified
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Durability and Packaging

• Temperature Constraint
• Met by purchasing industrial range components
• Sealed properly inside enclosure
• Packaging Constraint
• Currently, 4.94 x 2.25 x 1.2, too long
• With Parasitic Power only, would shorten design

19
Economics
20
Performance Testing

• Parasitic Power Circuit
• Projected 20 mA output
• Actual 7 mA output Not enough
• Test Range
• 2 meters TX 1.5 meters RX
• Exceeds design constraint
• Test Battery Life
• Measured total current draw of design 27 mA
• 6 hours of continuous use greatly exceeds
  design constraint
• Palm Pilot will monitor BER

21
Future Work

• FPGA Implementation
• Higher IrDA Protocol Stacks
• Add features to PIC, unused clock cycles
• Make it even lower power, exact cut off point for
  external resistance and 1 meter

22
Lessons Learned

• To decrease steady-state power draw, have switch
  transistors on Xcvrs IRED line and Vcc1/SD pin
• Dont change 2 things at once!
• Tantalum or Ceramic Capacitors It makes a
  difference
• Code Warrior is bad for Palm coding
• PACKAGING IS NONTRIVIAL!!!

23
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 and Dr. Ray Winton for their support
• My teammates for sticking with it

24
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.

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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.