Transcript Wireless Null Modem Infrared Palm Pilot Communication Device

Wireless Null
Modem
Infrared Palm Pilot
Communication Device
Team Members
• Team Leader:
– Stephen Porter
• Group Members:
– Huiyang Sim
– Shaun McFarland
– Peter Trenkle
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
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
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
Original Hardware Design
From RS-232
@ 19.2 kbps
RS-232
Line
Driver
Maxim 3100
Controls IrDA
Timing for the PIC
On-Board
UART PIC 16F873
On-Board
SPI Port
PIC Controls
capture of serial data
from SPI Port and
UART. This data is
then decoded
from/encoded into
IrDA compatible
data
To PALM
MAX3100
Infrared
Transceiver
From PALM
Redesigned Hardware
From RS-232
RS-232
Line
Driver
To control
TOIM4232 mode of
operation
To PALM
TOIM4232
IR XCVR
From PALM
PIC 16F873
Operates at 3.3V,
current draw < 2 mA
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
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
Parasitic Power
• Definition: Taking of power from the
serial port on one of the unused RS232 pins
• Supply power to Console (10–20 mA)
– Feasible if we increase external
resistance to IR Transceiver
– Pin outs for Voltage Regulator for
Battery Powered Option
Parasitic Power Schematic
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 @ 5mA
– Transistors 3.3V @ 15 mA
Parasitic Power Comparison
Voltage Regulator vs. Transistor
0.012
0.008
Transistor
0.006
Voltage Regulator
0.004
0.002
0
50
10
0
15
0
18
3
20
0
25
0
30
0
35
0
40
0
42
1
Amps
0.01
Resistance
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 @ 5 V
– New Design Enc/Dec = <2mA @ 3.3 V
IR XCVR Pinout
External Resistance
determines majority
of current drawn by
circuit
IRED
TX
PIC 16F873
RX
+5V
Vcc1/SD
Ground
TFDS4500
POWER DATA
Meters
Range Vs. Resistance
4
3.5
3
2.5
2
1.5
1
0.5
0
Simulated
Packaged
Prototype
1m
Specified
6
14
30
Ohms
70
120
POWER DATA
Current vs. Resistance
600
mA
500
400
Breadboard
300
Simulated
200
Packaged
100
0
6
14
30
Ohms
70
120
54mA
specified
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
Economics
PIC16F877
TFDS4500
DB-9 Plug
LM7805
74HCT04
MAX3100
MAX232A
Passives (R,C)
Materials (Packaging, PCB)
MAX3232A
2N3904 Transistors
1N4148 Diode
TOIM4232
Passives (R,C)
Materials (Packaging, PCB)
$4.50
$3.13
$2.00
$0.35
$0.25
$2.50
$0.85
$1.50
$8.95
$1.85
$0.25
$0.10
$4.00
$1.50
$5.95
$24.03 for old
$23.28 for new
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
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
Lessons Learned
• To decrease steady-state power
draw, have switch transistors on
Xcvr’s IRED line and Vcc1/SD pin
• Don’t change 2 things at once!
• Tantalum or Ceramic Capacitors – It
makes a difference
• Code Warrior is bad for Palm coding
• PACKAGING IS NONTRIVIAL!!!
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