West Mountain Radio Keyer Paddle User manual

QEX – May/June 2010 3
Reprinted with permission © ARRL
David Bern, W2LNX
8809 Cold Spring Rd, Potomac, MD 20854; [email protected]
A PS/2 Keyer: Using a Keyer
Paddle to Emulate a PS/2
Keyboard and Mouse
1Notes appear on page 8.
Would you like to operate your computer without a keyboard?
How about RTTY or PSK-31 without a keyboard? Now you can.
This article describes my first program-
ming project with a Microchip PIC®micro-
controller. The program for this project,
written in C, emulates a PS/2 keyboard and
a PS/2 mouse using a CW keyer paddle for
input.
Note: an earlier version of this article was
published in The 28th Annual ARRL and
TAPR Digital Communications Conference
Proceedings. The 28th Annual DCC was
held in Chicago, Illinois on September
25-27, 2009.
Over the past several years, I became
interested in learning how to program
Microchip PIC microcontrollers and I began
to look for an interesting project. I am an
experienced Cprogrammer, but I knew
nothing about PIC microcontroller program-
ming. My criteria for the project was that it
needed to have a well defined input, a well
defined output, and the circuit needed to
consist solely of a PIC microcontroller with
some light emitting diodes (LED). And,
importantly, it needed to be written in C.
At the 26th DCC, Milt Cram, W8NUE
and George Heron, N2APB introduced their
NUE-PSK digital modem.1The full details
of the NUE-PSK modem were published
in the Mar/Apr 2009 issue of QEX (NUE-
PSK Digital Modem Enables PSK31 Field
Operation Without Using a PC!), along with
a summary article in the March 2008 issue
of QST. The NUE-PSK modem is a small
device that provides portable PSK31 (and
now RTTY) operation without the use of a
personal computer. It does, however, require
a PS/2 keyboard for entering text. It occurred
to me that it could be more portable if the
large PS/2 keyboard were replaced with a
CW keyer paddle. A PIC microcontroller
would translate CW input sent on the paddle
into the output from a standard PS/2 key-
board. Hence, I found the idea for the project
for which I was looking. I would write a pro-
gram that runs on a PIC, and that emulates
a PS/2 keyboard using a keyer paddle for
input. Later on in the project, I wondered if
it was also possible to emulate a PS/2 mouse
with only two switch contacts and no other
moving parts.
Background
Morse Code
Morse code input is defined in the ITU
recommendation on the international Morse
code and is further described in an article in
Wikipedia.2, 3 The CW character and word
timings needed for this project are the length
of time of a dash relative to a dot, the length
of time between dots and dashes in a letter,
the length of time between letters and the
length of time between words.
The PS/2 Protocol
The output of a PS/2 keyboard and a PS/2
mouse follow the PS/2 protocol, which was
originally described in the IBM Personal
System/2 Hardware Technical Reference,
in the sections on the “101 and 102 Key
Keyboard” and the “Keyboard and Auxiliary
Device Controller” sections of the computer
reference manual, respectively.4, 5 Articles on
the Internet about the PS/2 protocol, the PS/2
keyboard protocol, and the PS/2 mouse pro-
tocol were most helpful.6, 7, 8 More recently,
an article describing a keyboard-game inter-
face using the PS/2 protocol appeared in
Nuts and Volts magazine.9
The physical PS/2 interface, shown in
Figure 1, used for the keyboard and mouse
connectors uses the PS/2 protocol. The PS/2
protocol is a two way synchronous protocol
used to communicate between a host and a
device. (See Note 6.) A host, typically, is a
personal computer and a device, typically,
is a keyboard or a mouse. In addition to a
clock line and a data line, there is a 5 V line
and a ground line. The PS/2 protocol uses
the clock line and the data line for sending
data. The frequency of the clock is within
the range of 10 to 16.7 kHz. Data is sent as
an 11 bit frame, starting with a zero start bit,
the eight data bits, with the least significant
bit first, an odd parity bit and one stop bit.
The device always generates the clock sig-
56
34
12
65
43
21
Male
(Plug)
Female
(Socket)
6-pin Mini-DIN (PS/2)
1 - Data 4 - Vcc (+5 V)
2 - Not Used 5 - Clock
3 - Ground 6 - Not Used
Figure 1 — The PS/2 ports for the keyboard
and mouse on personal computers use six
pin mini-DIN connectors.

4QEX – May/June 2010 Reprinted with permission © ARRL
nal. The host can request to communicate
with the device by pulling the clock line low
for at least 100 µs, then pulling the data line
low and then releasing the clock line back
high. The device responds by generating the
clock signal for the host to send its data to
the device. Finally, the device acknowledges
that it has received the complete data from
the host.
The PS/2 Keyboard Protocol
Each key on a PS/2 keyboard device is
identified by a unique scan code. Scan code
set 2 is commonly used today and it was
originally developed by IBM for the AT key-
board.10 The keyboard device sends to the
host the scan code of a key that is pressed;
a break code and its scan code is then sent
when that key is released. The host computer
can communicate with the keyboard device.
For example, the host commands the key-
board to light its Caps Lock LED when the
Caps Lock key is pressed.
The PS/2 Mouse Protocol
The standard PS/2 mouse device sends
the host its movement and button informa-
tion as a three byte packet. Mouse movement
information is sent as a relative position
change and is a signed nine bit two’s comple-
Figure 2 — This was my development breadboard. At the top of the photo, the four logic analyzer
probes are connected to the clock and data lines of the keyboard and mouse connectors.The
other two logic analyzer probes are connected to the –MCLR pin and a mark pin.
Figure 3 — This is the schematic diagram of the PS/2 Keyer.
ment binary number. Also, a standard PS/2
mouse has a left, a middle, and a right but-
ton. Initially, the host communicates with the
mouse to configure it after the host has deter-
mined whether the mouse is a standard PS/2
mouse or an enhanced PS/2 mouse.
The Project
Learning the PS/2 Protocol
To gain an understanding of the PS/2
protocol, I needed to see the data and the
clock lines at the wire level on a PS/2 cable.

QEX – May/June 2010 5
Reprinted with permission © ARRL
I assembled a six pin mini-DIN connector
breakout board from parts obtained from
SparkFun Electronics, a wonderful resource
for digital electronics hobbyists.11, 12 Sample
PS/2 protocol data came from an original
IBM AT computer PS/2 keyboard and a
Logitech PS/2 three button mouse. I pur-
chased an inexpensive logic analyzer from
Saleae.13 Since the PS/2 data bits are sent in
“reverse” order — least significant bit first
— I created a paper form to record the start
bit, eight data bits, parity bit, stop bit and any
acknowledgment bit. Later in the project, I
purchased a USBee SX logic analyzer, since
it can decode the PS/2 protocol for the host
and the device.14
PIC18F4520 Prototyping Boards
I needed to choose a PIC microcontroller
for my project. Rick Hambly, W2GPS, devel-
ops and sells time related products using PIC
microcontrollers and he recommended that
I use the 18F series PIC microcontrollers. I
purchased the PIC18F4520 development kit
from CCS: it includes a prototyping board,
and most valuably, an exercise booklet to
help get started.15 Note that the PIC18F4520
prototyping board and exercise booklet can
be purchased separately from the complete
kit. Other prototyping and demonstration
boards I have tried that use the PIC18F4520
are the PICDEM 2 Plus demonstration board
from Microchip, the Dem2PLUS demonstra-
tion board from Sure Electronics, and the
Olimex 40 pin bare prototyping board with
RS-232 from SparkFun.16, 17, 18 A USB ver-
sion of the Olimex 40 pin bare prototyping
board is also available.19
I assembled a prototyping board as shown
in Figure 2 by using a breadboard purchased
from Beginner Electronics, a PIC18F4520
microcontroller in the PDIP form factor,
two six pin mini-DIN connectors, an ICD
programming connector and a serial TTL
to RS-232 adapter.20, 21, 22, 23 I connected the
5 V power supply to the prototyping board
with a positive temperature coefficient (PTC)
resettable fuse device, available from Spark
Fun, at both mini-DIN connectors and at
the ICD programming connector.24 These
devices protect the prototyping board and
power supply sources against an accidental
short circuit. The two mini-DIN connectors
are connected to a personal computer using
a PS/2 keyboard-and-mouse-to-USB adapter
and two PS/2 male-to-male cables.25, 26 The
ICD connector is connected to a PIC pro-
grammer with a short cable. As luck would
have it, the receive and transmit pins of the
RS-232 adapter match the corresponding
input/output pins on the PIC18F4520. Note
the probes connected to the logic analyzer
in Figure 2.
The circuit schematic diagram shown in
Figure 3 consists of essentially one compo-
nent — the PIC18F4520 microcontroller.
The PS/2 keyboard connector, the PS/2
mouse connector and the CW keyer paddle
is connected to port B pins of the PIC to
take advantage of the internal pull-up resis-
tors provided within the PIC. No external
clock crystal or resonator is needed since the
internal 8 MHz clock within the PIC is used
instead.
PIC Development Tools
For the PIC programmer, I used the
Microchip PICkit™ 2 programmer/debug-
ger.27 The PICkit 2 is inexpensive and was
adequate for this project. It has a convenient
power management feature: it provides
power to the development board if it detects
that the board has no power. Also, power to
the board can be turned on and off from a
software menu item.
After evaluating free demonstration ver-
sions of several PIC Ccompilers, I chose the
CCS Ccompiler since it appears to best hide
hardware details of PIC microcontrollers
with library functions.28 The port input/out-
put library functions are easy to use and inter-
rupt service routines are easy to write. Also,
Rick Hambly, W2GPS, recommended the
CCS Ccompiler since he uses it extensively
for his work.
For the actual development environment,
I preferred to use the Microchip MPLAB®
integrated development environment (IDE)
instead of the one provided by CCS with
their Ccompiler suite.29 Note that the less
expensive CCS PCH Ccompiler instead of
the full CCS Ccompiler suite is sufficient
for this project since PCH integrates with the
MPLAB IDE.30
Learning PIC CProgramming
My first goal was to repeatedly blink an
LED on and off and to display “hello, world”
on a HyperTerminal serial terminal window.
I read several introductory books on PIC C
programming to get me started.31, 32, 33 There
are several other good books to read, as
well.34, 35, 36 Nuts & Volts and Circuit Cellar
magazines also have good articles on PIC
microcontroller development.37, 38
For program testing and debugging, I
learned to use LEDs and timing pulses on
an output pin to observe with a logic ana-
lyzer. I used the printf() function to print
configuration and debugging information
during program development and testing. I
also quickly learned not to introduce a timing
error in the code by putting a printf() in
the wrong place.
Writing the Program
This program is organized into three
software modules. The first module decodes
CW characters keyed in with the paddle. The
invalid CW character di di dah dah is used
to indicate that the next character entered
is a command code. Some command codes
are keyboard Enter, keyboard Caps Lock, an
Table 1
The Parts List to Build the PS/2 Keyer on a Circuit Board
Part Quantity Part Name Vendor Part Number
C1, C2 2 0.1 µF 50 V 10% PC-Mount Capacitor Digi-Key BC1148CT-ND
D5 1 Red round diffused lens LED Digi-Key P589-ND
R1-R5 5 330 Ω¼ W resistor Digi-Key P330BACT-ND
R6 1 10 kΩ¼ W resistor Digi-Key 10KQBK-ND
U1 1 40 pin IC socket Digi-Key 3M5471-ND
U1 1 PIC18F4520-I/P Digi-Key PIC18F4520-I/P-ND
4 Self-Stick Rubber Feet Digi-Key SJ5012-0-ND
J1, J3 1 PS/2 keyboard extension cable with purple connectors Micro Center SKU: 133314
J2, J4 1 PS/2 mouse extension cable with green connectors Micro Center SKU: 133272
J4 1 ¼ inch In-Line Stereo Audio Jack RadioShack Catalog #: 274-141
D1-D4 4 Green rectangular clear lens LED SparkFun SKU: COM-08532
Microchip PICkit 2 microcontroller programmer Digi-Key PG164120-ND
Saleae Logic logic analyzer SparkFun SKU: TOL-08938
Pro USB Converter: USB to PS/2 Keyboard and Mouse Micro Center SKU: 919712

6QEX – May/June 2010 Reprinted with permission © ARRL
error code and a switch to mouse mode. The
error code generates the appropriate number
of backspace characters to the beginning of
a word just entered. CW is translated into
ASCII text characters using a lookup table.
The paddle dot and dash contacts are con-
nected to pins RB4 and RB5, respectively, of
port B to take advantage of the change-on-
input interrupt feature. This allows the PIC to
go to sleep and consume practically no power
while waiting for an interrupt to occur when a
paddle lever is pressed.
Keyer paddle switch contact bounce
was probably the most challenging problem
of this project. A paper on switch bounce
convinced me that a keyer paddle without
any switch contacts, such as the Touchkeyer
paddle is necessary for this project.39, 40 An
internal timer interrupt is used to measure
time between dots and dashes. Using port B
input interrupts and timer interrupts simpli-
fied the code.
The second module emulates a PS/2
keyboard using the PS/2 protocol. ASCII
characters are translated into PS/2 keyboard
scan codes using a lookup table. The lookup
table has every character of a PS/2 keyboard,
including those not found in Morse code.
It was a thrill to first see the letter Q gener-
ated by the PIC microcontroller appear in a
NotePad text editor window!
The third module emulates a PS/2 stan-
dard three-button mouse. It generates PS/2
mouse button clicks and mouse pointer
movement from the keyer paddle input.
Clicking — briefly pressing — the left
paddle lever generates a left mouse button
click and, correspondingly, clicking the right
paddle lever generates a right mouse button
click. Mouse pointer movement is controlled
by pressing and holding the paddle lever:
the left contact controls the left-right mouse
pointer movement; the right contact con-
trols the up-down mouse pointer movement.
Pressing both sides moves the mouse pointer
along one diagonal direction or the other
diagonal direction. Hence, there are eight
possible mouse movement directions, and it
is possible to move the mouse pointer in an
Figure 4 — On the printed circuit board, there is a green LED in a transparent plastic lens
next to each cable connection. Hot glue is used to protect and secure the connections from
the PS/2 cables to the circuit board.The circles in the corners indicate where rubber feet are
placed under the circuit board.
Figure 5 — This photo shows a PICkit 2 programming cable wired using the connections
shown in Table 2. Hot glue protects the cable connections to a small prototyping board.The
dark colored dot on the top left corner of the perf board is oriented with the white triangle
on the PICkit 2.
Table 2B
Connections from the PICkit 2 Programmer Male Connector to a PS/2 Male
Connector PICkit 2 Programming Cable
Pin PICkit 2 Male Connector Pin PS/2 Male Connector
1 –MCLR 2 –MCLR
2 VDD 4 VDD
3 ground 3 ground
4 ICSP PGD 1 ICSP data
5 ICSP PGC 5 ICSP clock
6 not connected 6 not connected
Table 2A
PS/2 Mouse Extension Cable
with Green Connectors and PS/2
Keyboard Extension Cable with
Purple Connectors
Pin Wire Color
1 Black
2 Violet
3 Red
4 Green
5 Yellow
6 Blue

QEX – May/June 2010 7
Reprinted with permission © ARRL
Figure 6 — This shows a CW paddle cable wired using Table 3B.
octagon. Pressing for longer than about three
seconds causes the mouse pointer to move
faster on the screen. A command code of
three left clicks switches the program back to
keyboard mode. Again, it was fun to see the
mouse pointer move by itself in a continuous
circle on the screen during initial testing. It
took about two weeks of testing and experi-
menting with different mouse pointer move-
ment policies to get something reasonable to
control mouse pointer movement.
Testing during software development
was not difficult. A PS/2 keyboard and
mouse to USB adapter, a logic analyzer and
LEDs were used. During program startup,
the PIC would send a PS/2 keyboard and a
PS/2 mouse device reset code via the PS/2
to USB adapter to the host computer. The
computer would then respond with PS/2
device configuration command codes. This
made it unnecessary to repeatedly plug and
unplug the adapter USB connector in and
out of the USB port on the computer. I used
a logic analyzer to help my understanding of
the host-to-device initial configuration dialog
and for debugging my generated PS/2 key-
board scan codes and PS/2 mouse packets.
I connected the logic analyzer probes to the
PS/2 keyboard and the PS/2 mouse clock and
data lines. Also, additional mark pulses were
generated at points of interest in the code
to identify logic analyzer points of interest.
LEDs connected to pins on port A indicated
program activity. A general status LED, an
LED for the PS/2 keyboard port, and an LED
for the PS/2 mouse port were used.
Building a Circuit Board
After the 2009 Digital Communications
Conference, I designed a printed circuit board
Table 3A
Cable From Bencher CW Paddle
to a ¼ Inch Stereo Phone Plug,
RadioShack Catalog no.: 274-139.
Paddle Contact ¼ Inch Stereo
Phone Plug
Dot Left Tip
Dash Right Ring
Ground Sleeve
Table 3B
Connections Between a ¼ Inch Stereo
In-Line Jack, RadioShack Catalog no.:
274-141, and a PS/2 Male Connector.
CW Paddle Cable
¼ Inch Stereo In-Line Jack PS/2 Male
Connector
Dot Brass Tab 5
Dash Silver Tab 1
Ground 3
as shown in Figure 4. A PS/2 mouse exten-
sion cable with green connectors and a PS/2
keyboard extension cable with purple con-
nectors were cut in half and attached to the
circuit board with hot glue. The male green
and purple connectors are connected to the
corresponding purple and green female con-
nectors of the PS/2 keyboard-and-mouse-to-
USB adapter.
Table 1 provides the parts list of readily
available components to construct a circuit
board. Figure 5 shows a PICkit 2 program-
ming cable wired according to the informa-
tion in Table 2.
Figure 6 shows a CW paddle cable. On
one end of a connecting cable, I wired an
in-line ¼ inch stereo phone jack and on the
other end I used a PS/2 male connector, wired
according to Table 3B.
A sample program is shown in Figure 7.
It continuously blinks all the port LEDs. This
program is useful for doing a basic test of the
circuit board after its construction.
Future Enhancements
The current version uses a PS/2 key-
board-and-mouse-to-USB adapter to con-
nect the PIC18F4520 microcontroller to the
host computer. My next version will use a
PIC18F4550 microcontroller, since it con-
tains an internal USB interface, eliminating
the need for a PS/2-to-USB adapter.
Availability
The source code and the Express PCB
circuit board files for this project are avail-
able for download from the ARRL QEX
Web page.41 The source code is released
under the GNU General Public License,
version 2 (GPLv2); the files for the printed
circuit board are released under The TAPR
Open Hardware License Version 1.0 (May
25, 2007).
Conclusion
This is an interesting and enjoyable proj-
ect. I hope that this article inspires you to start
a Microchip PIC microcontroller program-
ming project. You can incrementally develop
a microcontroller project of moderate com-
plexity by systematically testing at every step
of the way. Microchip PIC microcontrollers,
programming tools and software develop-
ment tools are readily available and are rela-
tively inexpensive.
This project may be of possible use by
people who have limited physical mobility
who cannot use a conventional keyboard or
a mouse. This could allow them to type on a
computer or to manipulate a mouse pointer
using just two switch contacts. Coupled with
a “Puff and Sip Key,” described in the March
2004 issue of QST, the PS/2 keyer could
allow hands free operation of a computer.42
Acknowledgements
I would like to thank the following people
for helping me with this project in some way:
Adam Bern, KB3KVD, for being my keyer
paddle mouse tester, Jim Johns, KA Ø IQT, for
enlightening conversations about Microchip
tools, Joe Julicher, N9WXU, for suggesting
the PICkit 2 programmer, Larry Wolfgang,
WR1B, for convincing me to work on this
project, Milt Cram, W8NUE, and George
Heron, N2APB, for developing their NUE-

8QEX – May/June 2010 Reprinted with permission © ARRL
PSK modem, Rick Hambly, W2GPS,
for giving me guidance, and Steve Bible,
N7HPR, for encouraging me to write up this
project for the 2009 Digital Communications
Conference.
Notes
1Milton Cram, W8NUE, and George L. Heron,
N2APB, “NUE-PSK31: A digital modem for
PSK31 Field Operation...Without Using a
PC!,” 2007 TAPR and ARRL 26th Digital
Communications Conference Proceedings,
Hartford, Connecticut: ARRL.
2International Morse code,
“RECOMMENDATION ITU-R M.1677,”
International Telecommunication Union,
2004; available at www.godfreydykes.info/
international morse code.pdf
3Morse code, Wikipedia, The Free
Encyclopedia; http://en.wikipedia.org/wiki/
Morse_code
4Keyboard 101- and 102-Key, IBM Personal
System/2 Hardware Interface Technical
Reference — Common Interfaces, 1990;
www.mcamafia.de/pdf/pdfref.htm
5Keyboard and Auxiliary Device Controller,
IBM Personal System/2 Hardware Interface
Technical Reference — Common Interfaces,
1990, www.mcamafia.de/pdf/pdfref.htm
6Adam Chapweske, The PS/2 Mouse/
Keyboard Protocol, 2003; www.computer-
engineering.org/ps2protocol/
7Adam Chapweske, The PS/2 Keyboard
Interface, 2003; www.computer-engineer
ing.org/ps2keyboard/
8Adam Chapweske The PS/2 Mouse
Interface, 2003; www.computer-engineer
ing.org/ps2mouse/
9Jochen Jahn, “Keyboard-Game Interface,”
Nuts & Volts Magazine,Dec 2009, pp 30-34.
10Adam Chapweske, Keyboard Scan Codes:
Set 2; www.computer-engineering.org/
ps2keyboard/scancodes2.html
11SparkFun Electronics, MiniDIN 6-Pin
Connector, SKU: PRT-08509; www.
sparkfun.com/commerce/product_info.
php?products_id=8509
12SparkFun Electronics, MiniDIN 6-Pin
Connector Breakout, SKU: PRT-08651;
www.sparkfun.com/commerce/prod-
uct_info.php?products_id=8651
13Saleae LLC, Saleae logic analyzer; www.
saleae.com/logic/
14CWAV, Inc, USBee SX logic analyzer; www.
usbee.com/sx.html
15CCS, Inc., PIC18F4520 Development
Kit; www.ccsinfo.com/product_info.
php?products_id=18F452kit
16Microchip Technology Inc., PICDEM 2 Plus,
Part Number: DM163022; www.microchip.
com/stellent/idcplg?IdcService=SS_
GET_PAGE&nodeId=1406&dDocName=
en010072
17Sure Electronics Co, Hybrid of PIC18F4520
Dem2PLUS and Low Power Demo Board;
www.sure-electronics.com/product/
goods.php?id=24 and www.sureelectron
ics.net/goods.php?id=24
18SparkFun Electronics, 40 Pin PIC
Development Board, SKU: DEV-00021;
www.sparkfun.com/commerce/prod
uct_info.php?products_id=21
19SparkFun Electronics, 40 Pin PIC
#include <18F4520.h>
#use delay(internal=8MHZ)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#define PORT0_LED PIN_A0
#define PORT1_LED PIN_A1
#define PORT2_LED PIN_A2
#define PORT3_LED PIN_A3
#define DELAY 250
void blink_port_LEDs(void);
/* -------------------------------------------------- *
* this program continuously blinks all the port LEDs *
* -------------------------------------------------- */
void main(void)
{
delay_ms(DELAY);
printf(“Figure 7 sample program... hello\r\n”);
for (;;) {
blink_port_LEDs();
}
}
/* --------------------------------- *
* this routine blinks each port LED *
* --------------------------------- */
void blink_port_LEDs(void)
{
output_high(PORT0_LED); delay_ms(DELAY);
output_low(PORT0_LED); delay_ms(DELAY);
output_high(PORT1_LED); delay_ms(DELAY);
output_low(PORT1_LED); delay_ms(DELAY);
output_high(PORT3_LED); delay_ms(DELAY);
output_low(PORT3_LED); delay_ms(DELAY);
output_high(PORT2_LED); delay_ms(DELAY);
output_low(PORT2_LED); delay_ms(DELAY);
}
Figure 7 — This is a sample Cprogram for the PIC18F4520 using the CCS Ccompiler.

QEX – May/June 2010 9
Reprinted with permission © ARRL
Development Board with USB, SKU: DEV-
00022; www.sparkfun.com/commerce/
product_info.php?products_id=22
20Beginner Electronics, Breadboard and Wire
Kit; www.beginnerelectronics.com/begin
ner/Products.php
21Microchip Technology Inc,
PIC18F2420/2520/4420/4520 Data
Sheet: 28/40/44-Pin Enhanced Flash
Microcontrollers with 10-Bit A/D and nano-
watt Technology (document DS39631E),
2008; www.microchip.com
22SparkFun Electronics, Adapter board
for Microchip ICD and ICD2; www.
sparkfun.com/commerce/product_info.
php?products_id=193
23HVW Technologies, RS-232 Driver Module
— DCE; www.hvwtech.com/products_
view.asp?ProductID=289
24SparkFun Electronics, PTC Resettable
Fuse, SKU: COM-08357; www.spark
fun.com/commerce/product_info.
php?products_id=8357
25Inland Pro USB Converter USB to PS/2
Keyboard and Mouse, SKU: 919712; www.
microcenter.com/single_product_results.
phtml?product_id=0230515
26Cable Club, 6 ft PS/2 Keyboard and Mouse
Interface Cable (Male/Male), part: BC20277-
6; www.cableclub.com/keyboard-mouse-
interface-cable-malemale-p-797.html
27Microchip Technology Inc, PICkit 2
Development Programmer/Debugger;
www.microchip.com/stellent/
idcplg?IdcService=SS_GET_PAGE&node
Id=1406&dDocName=en023805
28CCS, Inc, Compiler Exclusively for Microchip
PIC®MCUs, www.ccsinfo.com/content.
php?page=compilers
29Microchip Technology Inc, MPLAB
Integrated Development Environment;
www.microchip.com/stellent/
idcplg?IdcService=SS_GET_PAGE&nod
eId=1406&dDocName=en019469&part=S
W007002
30CCS, Inc, PCH Command-line Compiler
for PIC18 MCU parts; www.ccsinfo.
com/product_info.php?cPath=Store_
Software&products_id=PCH_full
31Benson, David, C What Happens, Using
PIC®Microcontrollers and the CCS C
Compiler, Hayden, Idaho; Square 1
Electronics, 2008; www.sq-1.com/cwhtoc.
html
32Chuck Hellebuyck, Beginner’s Guide To
Embedded CProgramming: Using the
PIC®Microcontroller and the HITECH
PICC-LiteTM CCompiler, Milford, Michigan;
Electronic Products, 2008, ISBN: 978-
1438231594; www.elproducts.com/
embeddedcbook.htm
33Martin P Bates, Programming 8-bit PIC
Microcontrollers in C: with Interactive
Hardware Simulation, Oxford, UK: Newnes
Press, 2008; ISBN: 9780750689601
34Chuck Hellebuyck, Beginner’s Guide to
Embedded CProgramming — Volume
2: Timers, Interrupts, Communication,
Displays and More, Milford, Michigan:
Electronic Products, 2009; ISBN: 978-
1448628148, www.elproducts.com/
embeddedcbook2.htm
35Dogan Ibrahim, Advanced PIC
Microcontroller Projects in C: From USB
to RTOS with the PIC 18F Series, Oxford,
UK: Newnes Press, 2008; ISBN: 978-
0750686112
36Richard H. Barnett, Sarah Cox, Larry
O’Cull, Embedded CProgramming and
the Microchip PIC, Clifton Park, New
York: Delmar Learning, 2004; ISBN: 978-
1401837488
37Nuts & Volts Magazine, The Magazine for
the Electronics Hobbyist, ISSN 1528-9885;
www.nutsvolts.com/
38Circuit Cellar, The Magazine for Computer
Applications,ISSN 1528-0608; www.
cuitcellar.com/
39Jack G. Ganssle, A Guide to Debouncing,
Rev 3: June, 2008; www.ganssle.com/
debouncing.pdf
40CW Touchkeyer touch paddle, model
P1PADW; www.cwtouchkeyer.com/
P1PADW.htm
41The program source code file and circuit
board pattern files in ExpressPCB format
are available for download from the ARRL
QEX Web site. Go to www.arrl.org/qexfiles
and look for the file 5x10_Bern.zip.
42Gary Gordon, K6KV, “Build a Puff-and-Sip
Key,” March 2004 QST, pp 31-32.
David Bern, W2LNX, was first licensed in
1979 as N2AER with an Advanced Class and
upgraded to an Amateur Extra Class in 2000.
Later, he obtained his W2LNX vanity call sign
since he is also an avid Linux enthusiast. As a
high school student, he earned his First-Class
Radiotelephone Operator License with Ship
Radar Endorsement. In 1977, he earned a
BS in Computer Science from City College of
New York and then in 1983 earned an MS in
Computer Science from New York University.
He is a professional software developer and
also an adjunct professor of engineering at
Montgomery College, Rockville, Maryland. He
prefers building and experimenting with ham
radio projects to operating but enjoys operat-
ing QRP digital modes in the summer with his
son Adam, KB3KVD, in the Virginia moun-
tains. Currently, he is learning microcontroller
programming and digital signal processing.