Servo magazine 10 2008

10.2008
VOL. 6 NO. 10
SERVO 10.2008
5
34
A Digital RF Datalink
by Fred Eady
When your robots need to
communicate, but can’t see each
other, short-distance signaling using
low-power RF solves the problem.
40
Getting Control With the
Propeller: Part 2
by David Carrier
Controlling servos.
44
Get a Starter Motor
Runnin’ in Your Robot
by Steven Schmitt
Auto star
ter motors are often
overlooked for use in robot building.
However, they make a good choice
for power since they are almost
always series wound, inexpensive,
and readily available.
49
Counting on the Tried and
True Schmitt Trigger
by Margaret Toebes
See how one team at the North
Carolina Science Olympiad put this
classic circuit to work.
52
The Pico ITX Johnny 5
Project
by Andrew Alter
Part 2 covers the concept and
implementation of PC-
based robotics.
56
RoboGames 2008
by Samuel Coniglio
This world class event continues to
not disappoint year after year.
60
External Interface for the
NXT Robotic Brick
by Dennis Bogden
Using Robot C software and
integrated circuits, you can interface
your own sensors and actuators to
the NXT brick.
PAGE 56
Features & Projects
Due to extraterrestrial activity, the “Build the Ultimate
Robot” series by Michael Simpson will continue in the
November issue. We apologize for any inconvenience.
TOC Oct08.qxd 9/3/2008 1:42 PM Page 5
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TECHNICAL EDITOR
Dan Danknick
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CONTRIBUTING EDITORS
Jeff Eckert Tom Carroll
Gordon McComb David Geer
Dennis Clark R. Steven Rainwater
Fred Eady Kevin Berry
Andrew Alter Dennis Bogden
Sam Coniglio Margaret Toebes
Steven Schmitt David Carrier
James Baker Mike Jeffries
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William Smith Camp Peavy
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Copyright 2008 by
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Size Matters
W
hen Parallax announced their
new 12 VDC motors with
mount, wheels, and position
controller, I couldn’t resist picking up
a kit ($280). Finally, a ‘standard’ drive
system designed for medium-sized
mobile robots from the company
behind the BASIC Stamp and the
Boe-Bot.
The verdict? In short, the kit is
first-class. Not only are the aluminum
components beautifully machined
and professionally finished, but the
two 12 VDC motors are powerful
and the gearing is aggressive —
expect about 150 RPM at 1.5A and
no load. Furthermore, assembly
instructions and example Stamp
source code are straightforward
and easy to follow. It took me
all of 20 minutes for basic
assembly, including mounting
the quadrature encoder
assembly and inflating the
pneumatic tires.
I paired my motor kit with a
pair of the recommended HB-25
controllers ($50 each) from
Parallax. The controllers are
hefty, with built-in heatsinks and
cooling fans, and at less than three
ounces, add little to the overall
weight of about six pounds for the
pair of motors.
Is the kit perfect for every
robotics application? Of course not —
no general-purpose kit could be. For
example, the pneumatic 6” tires;
while well executed, are overkill for
my needs (an indoor balancing bot
platform) given their relatively small
diameter and inherent stiffness. I
replaced the inner tubes with zero
maintenance foam tubing. It’s a trick
I picked up from working with Traxx
wheels. Want a stiffer, more
supportive ride? Simply use denser
foam inserts in the tires.
Another consideration is ground
clearance for the motor and motor
mount. There’s only about an inch of
clearance from the rectangular motor
mount to the contact surface. This
shouldn’t be a problem if your robot
is going to be working on pavement,
carpet, or even a mowed lawn.
However, if you’re thinking of
running your robot down gravel
roads and rough terrain, you might
want to consider protecting the
Mind / Iron
by Bryan Bergeron, Editor

Mind/Iron Continued
6
SERVO 10.2008
Mind-IronOCT08.qxd 9/3/2008 2:58 PM Page 6
motors from accidental impact with a sheet of plastic or
even a layer of electrical tape.
If you’re thinking of moving from a Boe-Bot or other
small mobile robot platform to something based on the
Parallax wheel kit, take a moment to consider what’s
involved. You’re not simply replacing small, inexpensive,
lightweight servos with a heftier, more powerful (and
more expensive) drive system; you’ll have to upgrade your
entire development infrastructure.
For starters, you’ll have to stock up on heavy duty
aluminum stock — sheet metal, brackets, and fasteners. I’m
not talking about the solid chassis designs used to create
heavy-duty battle bots, but stock that’s significantly more
substantial than the easily workable aluminum and plastic
used with a typical carpet roamer.
Then there’s the issue of power. Forget about using a
AA battery pack. Instead, think 12V gell cell or — better
yet — a pair of six-cell, 7.2V NiMh battery packs sold for
R/C vehicles. I’ve had great results with the Dura Trax
six-cell, 7.2V, 4.2 Ah pack ($43 each) available from Tower
Hobbies (www.towerhobbies.com). While you’re on the
Tower Hobbies website, pick up a few sets of two-pin Ultra
Plugs by W.S. Deans ($3/set). Try these quick connect, low
resistance plugs for your battery connections and you’ll
never want to use a Molex connector again.
Because of the mixed voltages required — 12 VDC for
the Parallax motors or HB-25 motor controllers and 5V/3V
for the microcontroller and sensors — you should consider
a high-efficiency DC-DC converter. My favorite is
the programmable, three-channel RGi Power
Commander (($200), available from CrustCrawler
(www.crustcrawler.com). I use it to convert the 14.4
VDC from a pair of NiMh battery packs to 12V, 5V, and
3V, to power the motors, sensors, and Parallax Propeller
chip, respectively. Alternatively, you can use separate
battery packs and dedicated voltage regulators for each
voltage — but this wouldn’t be my first choice because of
the additional weight and space requirements.
You’ll also have to consider your tools. As noted
above, you won’t be working exclusively with easily
bendable aluminum, but you’ll have to learn to handle
heavy-duty stock. And this means you’ll probably have to
upgrade to heavy-duty tools — no more bending the
aluminum chassis with needle-nose pliers. Think bench
vise and rubber hammer.
Given the added expense of a medium-sized robot
over something that can fit in your hand, why make the
move? For one, you can create something practical — a
robot to fetch the paper, move a tray of food from one
room to another, or bring your medicines when they’re
prescribed, for example. You can also drop a laptop or
even a computer motherboard on a medium-sized platform
and have carrying capacity to spare. If you do decide to
make the move — with or without the Parallax motors —
drop me a line and a photo to share with your fellow
readers.
SV
ISP
programming
connector
push-on/push-off
power button
reset
button
piezo buzzer
30:1 micro
metal
gearmotors
user pushbuttons
removable 8x2
character LCD
battery charger
connector
optional
power LED
5 reflectance sensors on underside
4 AAA
batteries
(not included)
* High-traction silicone tires
* Speeds exceeding 3 ft/sec
using innovative constant-
voltage motor supply
robot diameter is 3π cm (~3.7 inches)
Item #975
$99.95
The Pololu 3pi robot is a high-performance, compact
mobile platform featuring:

* Two metal gearmotors
* Five reflectance sensors
* 8×2 character LCD
* Three user pushbuttons
* Buzzer and LEDs

All peripherals are connected to an ATmega168
microcontroller running at 20 MHz, with free C-programming
tools, libraries, and support for the Arduino environment.
Find out more at www.pololu.com/3pi or by calling 1-877-7-POLOLU.
SERVO 10.2008
7
Mind-IronOCT08.qxd 9/3/2008 2:59 PM Page 7
8
SERVO 10.2008
Fecundity Begets Rotundity
If you tip over the average robot,
all it can do is thrash around helplessly
until someone picks it up. But being
round and without external appendages,
the Groundbot™ from Rotundus
(www.rotundus.se) is always upright.
It also can move through mud, snow,
and sand without getting stuck, and,
being hermetically sealed, is pretty
much impervious to environmental
threats. It’s also tough enough to
survive drops of up to 10 ft (3 m).
Originally designed to explore the
surface of Mercury, Groundbot has
been modified for terrestrial chores
such as large-area patrol, explosive
gas monitoring, and remote
inspection. It can be fitted with up
to four cameras (up to 360° field of
vision), various sensors, night-vision
systems, microphones, and speakers.
Probably the most interesting
feature is the drive mechanism, which
basically relies on gravity. A controlled
pendulum is held close to the ground
when the bot is motionless. By lifting
the pendulum, it can be made to roll
in any direction. This produces speeds
of up to 6 mph (10 kph) and the
ability to handle inclines up to 20°.
In case you’re interested in the
details, Groundbot is 2 ft (0.6 m) in
diameter, weighs 55 lb (25 kg), and
normally runs six to eight hours on a
charge. Its operating temperature
range is -22° to 104°F (-30° to 40°C).
Bot Can Toot Your Flute
Proving that no idea is too silly to
endure if it draws government fund-
ing, the Anthromorphic Flutist Robot,
created by Atsuo Takanishi at Japan’s
Waseda University (www.waseda.jp),
is now in its fourth incarnation and
18th year of existence. Model WF-4RIV
(Waseda Flutist no. 4 Refined IV),
features 41 degrees of freedom that
have “enhanced its performance with
more natural notes and smoother
transitions between notes.” Specifically,
the lips and
tonguing mechanisms
have been redesigned to be more like
the corresponding human organs. Oh,
sure, there are the usual academic
rationalizations: “Clarifying the
human motor control while playing
the flute from an engineering point
of view . Enabling the communica-
tion with humans at the emotional
level of perception . Proposing novel
applications of humanoid robots .”
and so on. But imagine spending 18
years of your life on this thing. For a
demonstration, see www.youtube.
com/watch?v=lYDW2A5-Cbw.
Reportedly, work has begun on a
saxophone-playing version, so maybe
by 2026 Takanishi will come up
with something as amazing as, for
example, the Welte Orchestrion. First
demonstrated in 1862, it weighs in at
1,500 lb, operates from music rolls,
and drives 50+ pipes, bass, and snare
drums, and a triangle. To hear one,
visit www.asapackermansion.com/
orchestrion.html.
Saved by the Bear
At the other end of the utility
spectrum is the Battlefield Extraction-
Assist Robot (BEAR), developed by
Vecna Technologies (www.vecna.com),
a self-funded company created in
1998 and operated by alumni from
MIT, Harvard, Stanford, Yale,
Princeton, Berkeley, CMU, and other
assorted institutions.
Still in the prototype stage, BEAR
is envisioned as a marriage of three
elements: a powerful hydraulic upper
body, an agile mobility platform with
independent sets of tracked “legs,” and
The Waseda Flutist No. 4 vs. the Welte Orchestrion.
by Jeff Eckert
Robytes
The Groundbot mobile robot,
revamped for security duties.
Photo courtesy of Rotundus.
Robytes.qxd 9/2/2008 3:37 PM Page 8
“dynamic balancing behavior” (DBB).
DBB is how the robot hopes to balance
itself on the balls of its “ankles.” In
fact, the production model should be
able to remain upright whether bal-
ancing on its ankles, knees, or hips.
It has already demonstrated the
ability to pick up a realistically weighted
human dummy and carry it around for
50 minutes without a break. According
to Vecna, the purpose of the bear head
is to comfort soldiers who might be
put off by the otherwise “grotesque”
appearance of the machine.
New Robotics Conference
If you’re working on robotics at
the design level, you may be interested
in the upcoming IEEE International
Conference on Technologies for Practical
Robot Applications (TePRA). It’s a new
conference “aimed at catalyzing the
development of enabling technologies
and encouraging their adoption by robot
designers.” It’s intended to be a cross
between a dry academic conference
and an industrial trade show, so you
get an emphasis on practical
applications coupled with technical
presentations aimed at future
applications. The stated goals are
“to expose robot designers to new
enabling tools, techniques, and
technologies” and “to expose tool,
technique, and technology developers
to the needs of robot designers.”
The event is scheduled for
November 10th and 11th at the
Holiday Inn Select Hotel, Woburn,
MA. For details, visit www.ieee
robot-tepra.org.
Dragonfly V. 3
In July, the Delft University of
Technology (www.tudelft.nl) intro-
duced the third version of its artificial
dragonfly, the DelFly Micro micro air
vehicle (MAV). Weighing only 3 g and
with a wingspan of only 10 cm, it
flies by flapping its wings like an
insect. The remote-controlled device is
intended to be used someday for
observation flights in dangerous or
difficult to reach areas, and it already
can be equipped with a tiny 0.5 g
camera that transmits TV-quality
images to a ground station. Given
that it can fly continuously for only
about 3 min (at 5 m/s), it obviously
isn’t ready for commercial production.
But Micro is just a stepping stone to
the planned DelFly Nano (5 cm, 1 g),
which will be able to move independ-
ently using image recognition
software, hover like a hummingbird,
and even fly backwards.
SV
Robytes
SERVO 10.2008
9
Vecna’s BEAR robot as employed on the
battlefield. Photo courtesy of US Army.
The DelFly Micro MAV.
Photo courtesy of Delft U.
Heavy Metal R
o
bot Kit
Announcing
the Gears
Designed for Students and Professionals
L
Heavy Metal is engineered for rigors of daily use in classrooms,
summer camps, workshops, labs . . . even combat robots!
L
Assembles quickly using fasteners of same size/pitch and
threaded inserts. 10" wheel base, heavy gauge aluminum,
4-wheel drive, 3" rubber wheels, 3/8" axles, flanged
bronze bearings, #25 pitch steel chain and sprockets.
All drive components are keyed and broached.
L
Competition all-metal gearhead motors, gearbox
rated at 500 oz-in of continuous torque. Heavy Metal
accepts off-the-shelf engineering parts, plus
components and control systems from GEARS IDS,
FIRST* and VEX Robotics* kits.
Contact Mark Newby
mnewby@gearseds.com
sWWWGEARSEDSCOM
Lb for Lb
the World's
Toughest Robot
Chassis
Supports 200 lbs of
standing weight!
Heavy Metal 1 Kit includes chassis, motors, drive system, and wheels for $499.00.
*VEX Robotics is a mark of Innovation First, Inc. and FIRST refers to © US FIRST (Foundation for the Inspiration and Recognition of Science and Technology)
Robytes.qxd 9/3/2008 1:06 PM Page 9
10
SERVO 10.2008
You’re No. 1 . Really!
Ian Ingram, BigBot curator and
creator of the “You’re No. 1” robotic
foam hand and finger interpretation
atop the Andy Warhol Museum spoke
about the BigBots, beginning with his
own work (at my request).
The nearly seven yards of
Pittsburgh black and yellow foam
hand and index finger spread the love
by reaching out to visitors to say they
were no. 1. The hand moved, posi-
tioned itself, and pointed at various
visitor outposts miles away and
throughout the city using dual-axis
hydraulics. One axis was a hydraulic
motor and one was a hydraulic actuator.
The hydraulics gave the hand
two degrees of freedom (DOF) of
movement. The first DOF held the
hand straight up and twisted it
around while the second moved it
downward to point it at the outposts
or to wave at people. All the action
was automated by a small microcon-
troller, though the original plan was to
have kiosks at the outposts with
remote triggers to activate the hand
and point it in the specific direction of
the kiosk that triggered the response.
The robotic hand made use of
sensing and a limiting switch — a
gross encoder — which told the
robot when to stop and start its
movements. The hand was fitted
with a camera that lined up in varying
positions equal to a straight line to the
different outposts.
The PIC microcontroller was
brought to life using software created
in C programming. The software looks
for limit switch hits, making plans
for movement between where the
hand is and where it needs to go to
perform the pointing and waving,
according to Ingram.
The robot uses a motor to pump
fluid to create pressure to activate
and manipulate the hydraulics. The
hydraulic valves use solenoids and are
pushed by external signals from the
microcontroller. The structure of the
hand is steel weldments with
polyurethane foam similar to the
hands that people take to sports
games.
Semi-autonomous
Percussive Devices
Communicate Like
Crickets
The Crickets installation uses a
number of interconnected robotic
sculptures to imitate the action and
reaction of group communication
among packs of animals such as dogs
or insects. The robots are equipped
with wooden knockers controlled by
solenoids to tap out their noises.
Contact the author at geercom@alltel.net
by David Geer
Robot250 Features BigBots
Robotic Artwork that Interacts and Responds
Robot250 is a city-wide extravaganza of large scale interactive robot art projects, workshops,
festivities, events, and film held July 11-27 in Pittsburgh, PA. Sponsored by Carnegie Mellon
University, the University of Pittsburgh, and a number of local community groups like the
Heinz Endowments, the program features BigBots interactive robot displays with artistic themes.
Photos and caption information are
courtesy of Carnegie Mellon University.
The “You’re No. 1” BigBots
robotic installation by Ian Ingram
is a 20-foot tall robotic black
and yellow foam hand and finger
like the ones worn by fans of
Pittsburgh’s most famous sports
team. The maneuvering hydraulic
hand appeared on the roof of
the Andy Warhol Museum in
Pittsburgh as part of the
Robot250 Festival, which ran
July 11-27, 2008. Ingram, BigBot
curator, senior research
associate, and artist-in-residence
at Carnegie Mellon University,
built the big hand, which pointed
at passers-by around the city.
Geerhead.qxd 9/3/2008 9:31 AM Page 10
Connected by thin wires,
each robot communicates to
its closest neighbor whether it
is silent or drumming up a
storm. So, throughout the
group the robots set each
other off until the whole
colony is chirping away or they
turn each other off until they
are all quiet.
Each cricket is controlled by a
BASIC Stamp microcontroller and has
its own unique sound. Software
programming sets the action and
reaction in motion. The programming
uses a specific set of rules called “The
Game of Life” that says when a robot
starts knocking, the signal to its
neighbor is to start knocking, but
when all robots are knocking, one
robot must become silent and then
the others react in kind one by one
until all are silent.
Green Roof Roller
Coaster
Roof top plants and gardening
generally serve the building and
environment by providing an added
layer of insulation or contributing
oxygen. Serving the plants themselves
is a matter left unaccounted for,
until now.
The idea behind the Green Roof
Roller Coaster is to set the plants on a
continual ride up, around,
and down for their own
stimulation and amuse-
ment. In an attempt to
measure their pleasure,
the installation uses
sensors near the plants
to gauge humidity, CO
2
,
vibration, and leaf conduc-
tance. While these sensors
interpret the health of the small trees’
environment, this is only loosely and
perhaps humorously translated to the
degree of entertainment the plants
find from their constant motion.
The Look-See Tree
A mobile installation that looks
like a fallen tree houses five groups of
visible robotic animals that move and
interact with people as they sense
them coming near. The robots are
electrically powered and animated
using servo motors. They are connect-
ed via frameworks of gears and
linkage systems and are powered by
a hand-cranked electric generator.
One robot simulates a fox that
paws at the ground. Another group
of robots are birds whose chirping
resembles cell phones ringing or car
alarms sounding off. Still another
group are animals collecting garbage
from around the city to construct
their nests.
The Reach Robot
Sculpture
The Reach robot senses people’s
movements and gestures throughout
SERVO 10.2008
11
GEERHEAD
The “Green Roof Roller Coaster” BigBots
installation is a roller coaster that takes a
variety of grasses and other plants for a
wild ride above the Children’s Museum
of Pittsburgh. The installation uses
sensors to measure humidity, CO
2
,
vibration, and leaf conductance in an
attempt to determine how the plants
respond to riding on a roller coaster.
These robotic wood blocks
called “Crickets” tap with
wooden knockers in response
to neighboring bots that are
doing likewise.
The “Look-See Tree” is a
mobile tree sculpture
haven for robotic animals
and cell phones that
behave like animals.
The “Reach” robotic installation in the
PPG Place plaza interprets pedestrian
movement with a musical response. The
creation of artists Grisha Coleman and
Frank Broz, Reach consists of strands of
fiberglass that create a web across the
plaza, a plane in which a LIDAR (LIght
Detection And Ranging) system senses
movement and triggers musical
compositions from famed area African
American Jazz composers.
Geerhead.qxd 9/3/2008 9:34 AM Page 11
the PPG Place plaza using two LIDAR
(LIght Detection And Ranging)
technology systems that scan and
find ranges or distances between the
place of emission of laser light and
the position of the person sweeping
through.
One system aims its lasers across
the whole plaza and one scans down
from up high, creating a plane they
scan across to determine distance and
movement. “It tracks objects (people)
as they move through that plane,”
says Ingram.
The lasers determine people’s
positions relative to strands of fiber-
glass webbing strewn in criss cross
fashion across the plaza and 10 feet
above it. People who may be
“reaching” toward the strands to
stroke them as if they were strings on
an instrument will note an audible
response.
When people’s positions relative
to the strings are tracked and
captured by the lasers and pressure
sensors, this sets off musical
compositions reminiscent of famed
Pittsburgh area composers,
particularly African American Jazz
musicians.
While the installation and its
purpose may be confusing to some,
others will realize its purpose as their
actions set off the music. Patrons may
not only start the music with their
gesturing, but also “conduct” the
music by interacting repeatedly
with the webbing, and so with the
laser field.
People in different locations in the
plaza will activate different musical
effects and interludes.
Conclusion
Robots 250 and the BigBots
installations stir the curious soul to
investigate. It’s amazing how robotics
have become so much a part of our
lives and how closely they intertwine
themselves with the most expressive
of art forms. It is interesting to see
the skill level in robotics assumed by
those whose primary endeavor of
study is the arts.
SV
12
SERVO 10.2008
GEERHEAD
Robot250 home page
http://robot250.org
Robot250 events and exhibits
http://robot250.org/festival/
index.php
Robot250 types of events
http://robot250.org/festival/
types/index.php
Robot250 BigBots
http://robot250.org/festival/
bigbots
Robot250 photo gallery
http://robot250.org/media/gallery
RESOURCES
Geerhead.qxd 9/3/2008 9:35 AM Page 12
Q
. (In this case, not so much a question, but a
request. It was worded so well and completely
I felt that it would be disingenuous to simply
paraphrase, so I’ll quote and add comments later. I believe
in giving credit where credit is due.)
I enjoyed your column in the August issue of SERVO. I
really like the AVR microcontrollers and the gcc-avr compiler.
I wish you would mention a readily available and really
pretty simple IDE for the Atmel — Arduino. They’re at
http://arduino.cc/.
I’ve used this environment in several Introductory
Programming classes and it’s been a big hit. It meets
several of the criteria that your questioner brought up and
it has some cool features that, to me, contrast favorably
with the complexity of Eclipse.
1) The Arduino software Integrated Development
Environment is portable, and is available for Mac, Linux,
and Win32. Basically, it’s a small Java application that
allows editing and compiling C/C++ programs and that
launches gcc-avr in the background to do the actual
cross-compilation.
2) It’s simple — and while that means putting up with
some limitations, such as no real debugging — a lack of
complexity is also a big plus for beginners. Source code files
are easily assembled into “sketches,” which are held in
folders on your system. The look is very simple and clean,
with no makefiles or projects needed, and without the
cascade of panes, options, menus, and buttons that are an
unfortunate side effect of Eclipse’s power.
3) There’s a nice library built in. It has functions for easy
digital and analog I/O, along with most of the standard
C library. It’s all documented on the site.
4) You don’t need a programmer because it can directly
upload the compiled program into the chip. This is
possible because the chips come with a small bootloader
pre-installed. So when you press the appropriate button in
the Arduino IDE, a serial or USB to serial cable carries the
generated code into the chip. Then you just press reset and
go. Very easy, and this is a feature I appreciate as someone
who works a lot with beginning programming students.
5) A number of inexpensive boards are available. Some
examples can be found at http://moderndevice.com/
and http://wulfden.org/TheShoppe.shtml.
6) There’s a ton of software and hardware already available
for the basic hardware. As an example, www.freeduino.
org/ lists hundreds of projects and reusable hardware and
software ideas.
Anyway, sorry for the long mail, and keep up the good
work, I enjoy your column.
— Jerry Reed
Adjunct Professor of Computer
Programming and Applications,
Valencia Community College
A
. Thanks Jerry for the kudos and the lead. I had heard
of Arduino but thought of it (initially) as only another
interpreter chip for a token-based compiler. Little did
I realize just how WRONG I was! The Arduino is an open
source language built on top of C++ that simplifies the task
of writing code for an embedded processor. The Arduino
project abstracts the embedded processor to make it a
hardware object that can be run on its own or interfaced
to the computer to talk to other programs. The obvious
computer interface is the Processing language upon which
the Arduino language is built. This hardware-oriented
language is called Wiring; it simplifies many of the tasks
that a beginner would like to do with an embedded
processor. Of course, this act of simplifying that
programming means that some of the capability of the
processor (an Atmel ATMEGA8 or ATMEGA168) is reduced
or lost (no interrupts or PWM capability), but for many
Tap into the sum of
all human knowledge
and get your questions answered here!
From software algorithms to material selection, Mr. Roboto strives to meet you
where you are — and what more would you expect from a complex service droid?
by
Dennis Clark
Our resident expert on all things
robotic is merely an email away.
roboto@servomagazine.com
SERVO 10.2008
13
MrRoboto.qxd 9/2/2008 11:16 AM Page 13
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SERVO 10.2008
just looking for learning embedded programming this is a
VERY painless way to learn. Arduino boards (or other
independent offshoots) are fairly cheap and capable, so the
introductory price is also low. Because Arduino is open
sourced, you aren’t locked into anyone’s boards at all. Part
of the Wiring environment’s IDE includes the ability to turn
any ATMEGA8 or ATMEGA168 into an Arduino target; as
long as you have a programmer and downloader software
that can directly program the ATMEGA part. After you
have the bootloader installed, all you need is a serial port
connection (Bluetooth, ZigBee, or any other wireless
connection will work, as well!) and you’re off and running.
The Arduino site mentioned above is a good start
to learn this environment — which is Java based
and runs on any platform that has Java installed.
There is even a little interface driver/program
named serproxy that comes with the install on
the Mac OS X operating system to simplify the
interface to another computer program to talk to
the Arduino board over a serial port. For more
information on the Processing language and
Wiring language, see the links http://processing
.org/ and http://wiring.org.co/. I’m going to
be looking into these resources in the future!
Q
. I have inherited a pile of parts. Among
these are five pairs of ultrasonic sensors.
At least, that is what I think they are.
One is marked on the back with a 40R and the
other with a T. I am assuming these are transmitters
(T) and receivers (R). There was a slip of paper
in the container with 40TR12B written on it.
I notice that ultrasonics are usually purchased
on circuit boards. Can you help me with a circuit design and
some software tips for making these work? Thanks.
— Anonymous
A
. The ultrasonic transducers that you have are from
Jameco, part number 139492. They are 40 kHz trans-
ducers which means that they resonate at 40 kHz,
and require a 40 kHz signal to make them work. There are
many, MANY sites on the Internet that detail various folks’
circuits to drive these devices. Here are a couple that I like.
The one shown in Figure 1 is located at www.e-arsenal.
net/robotics/sonar.html and seems a custom fit to your
transducers. It uses a
MAX232 serial port
driver to deliver a higher
voltage to the transducer
to increase the power
of the output signal
and a common op-amp
to sense the returning
echo. This circuit,
however, requires that
you send a 40 kHz
signal to the circuit;
typically you would use
a PWM output to do
this and wait for a
return echo on the pong
line. This circuit details
using a PIC16F628 to
handle all of the SONAR
details and uses a
similar but simpler
circuit to send and
receive SONAR signals
(see Figure 2). This
Figure 2. A PIC controlled SONAR circuit. Used with permission by GenerExe IT.
Figure 1. SONAR circuit 1.
MrRoboto.qxd 9/2/2008 11:16 AM Page 14

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