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Wireless Null Modem

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... a cheap, convenient alternative to a laptop interfacing to an ASCII display menu ... Data Link Design Guide,' http://www.hp.com/go/ir, Hewlett Packard, Palo ... – PowerPoint PPT presentation

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Title: 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

10
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
14
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

15
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
17
POWER DATA
54mA specified
18
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.

25
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.
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