Title: Wireless Null Modem
1Wireless Null Modem
- Infrared Palm Pilot Communication Device
2Team Members
- Team Leader
- Stephen Porter
- Group Members
- Huiyang Sim
- Shaun McFarland
- Peter Trenkle
3Abstract
- 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
4Design 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
5Major 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
6Original 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
7Redesigned 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
8Advantages 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
9Disadvantages 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
10Parasitic 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
11Parasitic Power Schematic
12Schematic
- 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
13Parasitic Power Comparison
14The 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
15IR XCVR Pinout
External Resistance determines majority of
current drawn by circuit
PIC 16F873
IRED
TX
RX
TFDS4500
Vcc1/SD
5V
Ground
16POWER DATA
1m Specified
17POWER DATA
54mA specified
18Durability 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
19Economics
20Performance 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
21Future 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
22Lessons 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!!!
23Acknowledgements
- 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
24References
- 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.
25References
- 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.