Monocular Autonomously- Controlled Snowplow - EEWeb

EEWeb 

PULSE 

Ohio University 

EEWeb.com 

Issue 53 

July 3, 2012 

Electrical Engineering Community

TABLE OF CONTENTS 

Frank van Graas, Maarten Uijt de Haag, 

and Wouter Pelgrum 4 

OHIO UNIVERSITY 

Interview with Frank van Graas, Maarten Uijt de Haag, and Wouter Pelgrum - Professors in the School 

of Electrical Engineering and Computer Science, Researchers with the Avionics Engineering Center 

Monocular Autonomously-Controlled 13 

Snowplow 

BY SAMANTHA CRAIG, MATTHEW MILTNER, DEREK FULK, 

WOUTER PELGRUM, AND FRANK VAN GRAAS 

Ohio University’s submission to the Annual Autonomous Snowplow Competition. 

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A solution for emebedded developers that enable them to respond quickly and easily to customer 

and market demands, last-minute design changes and competitive challenges. 

State Machine Heretic 25 

BY DAVE VANDENBOUT WITH XESS CORP. 

An overview of one and two-process state machines and their project applications. 

20 

RTZ - Return to Zero Comic 29 

EEWeb | Electrical Engineering Community Visit www.eeweb.com 3 

TABLE OF CONTENTS

INTERVIEW 

Ohio 

University 

Frank 

van Graas 

(rear), Maarten Uijt 

de Haag (front right), 

Wouter Pelgrum (front left) - 

Professors in the School of Electrical 

Engineering and Computer Science, 

Researchers with the Avionics Engineering Center 

Frank van Graas, 

Maarten Uijt de Haag, 

and Wouter Pelgrum 

How did you get into 

electronics/ engineering and 

when did you start? 

Frank: I built my first circuit when 

I was approximately 5 years old. It 

consisted of a 4.5-V battery, a switch 

and a light bulb. From that time on, I 

wanted to learn as much as I could 

about electronics, and by the time 

I was twelve years old, I already 

planned to get an advanced degree 

in electrical engineering. 

Maarten: Early on in high-school I 

became fascinated with electronics 

and spent a significant amount of 

time “playing” with commercially 

available electronics circuit kits. 

After that I moved on to building 

electronics-based alarm systems for 

my room and small robots that could 

move freely through our house. 

An even though I contemplated 

going in aeronautical engineering I 

decided in the end to get a degree 

in Electrical Engineering. 

Wouter: I have been always 

interested in engineering, especially 


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electrical engineering. As a little 

kid I wired AC light bulbs before I 

could read, invested all my money 

on Lego and spent countless hours 

building elaborate constructions. 

In high school I got myself into a 

wide range of activities, such as 

audio engineering, special effects, 

video productions, and wireless 

communications. 

How did you arrive at Ohio 

University? 

Frank: I was studying at Delft 

University of Technology in the 

Netherlands, finishing up the 

“engineers” degree. GPS had 

become one of my research 

interests, but it was difficult to find 

information about GPS in Europe. 

Through Delft University, I found out 

that Ohio University had an active 

differential GPS program with 

NASA to land helicopters. It turned 

out that one of my professors, Gerrit 

de Jong, knew a professor at Ohio 

University, Kent Chamberlin, from 

an electromagnetics conference in 

Spain. I contacted prof. Chamberlin 

and asked if I could come to visit 

for a few months. That all worked 

out and within 2 weeks I was 

working on the NASA program. 

When it was time for me to return 

to Delft University, I was offered a 

research associate position at Ohio 

and ended up finishing my Ph.D. 

there instead of at Delft University. 

Shortly before I graduated, a faculty 

position in Avionics opened up at 

Ohio. I couldn’t imagine a better 

position, so I applied and joined the 

faculty in 1988. 

Maarten: While I was studying at 

Delft University of Technology in 

the Netherlands, I met Dr. Michael 

Braasch from Ohio University and 

a former student of Dr. Frank van 

Graas. He was part of an exchange 

program between Ohio University 

and Deft University of Technology. 

I worked with him on Global 

Positioning System (GPS) related 

work for my M.S.E.E. and he served 

on my thesis committee. After 

finishing up my degree at Delft, I 

got a scholarship to go abroad and 

work for 6 months. I contacted Ohio 

University and went over there for 6 

months. At Ohio University I met Dr. 

Frank van Graas and he offered me 

a job as a research engineer with 

the Ohio University Avionics 

To me all phases of a 

project are exciting, 

starting with the 

concept, design and 

implementation to the 

operational testing and 

data analyses. - Frank 

Engineering center. Besides my 

regular job I did some substitute 

teaching for Frank and when he 

asked me if I wanted to get my Ph.D. 

I was excited. After finishing up my 

Ph.D. I became a visiting professor 

in 1999 and when a permanent 

position opened up in Electrical 

Engineering and Computer 

Science, I applied and got the job 

in 2000. 

Wouter: When I did my Masters at 

Delft University, Professor Durk van 

Willigen came back from retirement 

to be my advisor for my thesis on 

H-field antennas for Low-Frequency 

radionavigation systems. This work 

got me in contact with the navigation 

community, and also with the people 

from the Avionics Engineering 

Center at Ohio University, Frank 

van Graas especially. In 2005 Frank 

arranged for me to spend 6 months in 

Ohio, primarily to focus on finishing 

my Ph.D. dissertation. In 2006, just 

before finishing my Ph.D., I started 

my own company specializing on 

radionavigation and did a variety of 

projects for Ohio University. When a 

faculty position opened up at Ohio 

University in 2008 I applied and got 

the job, which I started in 2009. 

Can you tell us about your 

work experience/ history 

before arriving at Ohio 

University? 

Frank: During my student years, I 

was always working on challenging 

electronics projects, such as a 

telephone system that connected 

4 telephones to the same line 

and automatically kept track of 

the charges for each individual 

telephone, audio systems, power 

supplies, and sensitive magnetic 

field sensors. 

Maarten: During my student 

years, I worked on a variety of 

electronics project including the 

telephone distribution system at 

my fraternity. Also, I did some work 

as a software engineer at a small 

(15 people) chemical engineering 

company where I end up running 

the software department for a 

year. At Delft university I was 

furthermore a teaching assistant in 

the communications labs. 


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Wouter: When still in college I 

started a company that provided live 

video coverage of rowing races. We 

borrowed equipment from pretty 

much every electrical engineering 

research group of the university, 

ranging from high-end video 

cameras to experimental fiber optic 

video communication systems. That 

combined with home-brew wireless 

video and audio links, computer 

systems, and countless custombuild 

solutions we were able to 

provide a professional product at 

very low cost. Projects like these 

taught me to be creative, have 

risk-mitigation strategies for every 

conceivable situation in place, 

and, most importantly, to build an 

enthusiastic team of people to get 

the job done and to have fun while 

doing it. 

Next to my video production 

activities, I also jumped into Linux, 

and build a massive storage and 

content delivery system consisting 

of a robust cluster of dozens of 

unreliable network servers. Now, a 

decade later, I still apply the lessons 

learned from that project to every 

data collection we conduct. 

During most of my Ph.D. studies I 

worked for Reelektronika, a small 

company in the Netherlands. 

Although work and studies were on 

the same topic, it proved to be a great 

challenge to balance the short-term 

pressure from the company with 

the long-term goals of a Ph.D. At 

Reelektronika I worked on eLoran, 

a Low-Frequency radionavigation 

system, on the H-field antenna, 

receiver algorithms, receiver design 

and implementation, measurement 

campaigns, and data analysis. 

In 2006 I started my own company, 

consulting in radionavigationrelated 

areas. 

What have been some of your 

influences that have helped 

you get to where you are 

today? 

Frank: My father was a major 

influence on my career; he would 

occasionally help me with troubleshooting 

my projects, which helped 

me to realize that there aren’t always 

quick fixes or easy answers. He 

would build everything from scratch, 

including all his measurement 

instrumentation. Growing up, we 

were the first in our neighborhood 

with a black and white television 

because he built it himself. The 

drawback was that we were the 

last to switch to a color TV, since 

he always managed to fix his black 

and white product, no matter what 

went wrong. From that experience, 

I learned that it is important to know 

all the details of a project. 

Maarten: Even though my parents 

were no engineers, they very 

much encouraged my interests in 

electronic systems and aeronautics 

during my high-school years. When 

I got to college and started working 

on my M.S.E.E. my advisor, Dr. 

Durk van Willigen really stimulated 

my interests in electronics for 

aircraft (avionics). After my move 

to Ohio University Frank van Graas 

took over that role and also got me 

interested the teaching and student 

advising which made me decide to 

go into academia. 

Wouter: My parents always greatly 

supported and encouraged my 

interests in science and engineering. 

In college it was my M.S.E.E. and 

Ph.D. advisor Dr. Durk van Willigen 

who got me excited about the area 

of radionavigation and Dr. Frank van 

Graas who brought me in contact 

with Ohio University and has 

mentored me here in the US. 

Do you have any tricks up 

your sleeve? 

Frank: Learn all the basic concepts 

in math, physics and electrical 

engineering. Sooner or later, you’ll 

need them all in your career to solve 

a variety of problems. After a while, 

you’ll recognize the parallels and 

that it all connects to the same basic 

concepts. 

Maarten: Try to express your 

complex engineering problems in 

terms of basic concepts of electrical 

engineering. Furthermore, always 

ask yourself what you want to 

achieve with your electronics 

system, what you are going to use it 

for, and who is going to use it. 

Wouter: Prepare for everything, 

whatever can go wrong will go 

wrong at some point, no matter 

whether you are programming a 

software algorithm or are involved 

in the field-testing of a complex 

system. And then, typically, when 

you are fully prepared for every 

conceivable scenario and have 

backups for everything, you won’t 

need any of your backups because 

your system will just work… 

What has been your favorite 

project? 

Frank: I have several favorite 

projects, but it hard to top the project 

we did for FAA in 1994, when we 

leased an empty Boeing 757 over 

the weekend from the United Parcel 

Service in Louisville, KY, loaded it 


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up with two first-class chairs and 

a rack with electronics, hacked 

into the 757 autopilot to make it fly 

our GPS guidance instead of its 

trusted triple-redundant Instrument 

Landing System, flew to FAA’s test 

site at Atlantic City Airport, NJ, 

executed 50 automatic landings 

in a row, flew back to Louisville 

and unbolted the equipment while 

taxiing to the gate so that we could 

turn the aircraft back over to UPS 

to reconfigure and recertify the 

aircraft for overnight package 

delivery. This project was part of 

an FAA demonstration program to 

show that GPS can be used to land 

airplanes. 

Maarten: My favorite project was 

the design, implementation and 

flight test of a navigation system that 

uses on one or more airborne laser 

scanning systems (as are currently 

being used to build maps of large 

portions of the US). We first flew 

this system and a data collection 

onboard a NASA DC-8 at Dryden 

Research Center at Edwards Air 

Force base and Reno, NV. Next, 

we designed and installed a 

smaller, less expensive system on 

our DC-3 and performed various 

approaches to an airport in West 

Virginia while providing the pilot 

with the necessary guidance on an 

LCD display. This project was I part 

sponsored by NASA, the Air Force 

Research Laboratory and Northrop- 

Grumman. 

Wouter: I have been involved 

with many exciting projects. The 

most fulfilling moments are those 

when a team-effort leads to a great 

result. For example with my video 

productions where I had a team of 

great people making an excellent 

product. The technology had been 

painstakingly prepared and worked 

flawlessly, but the greatest joy is 

Prepare for 

everything, whatever 

can go wrong will go 

wrong at some point, 

no matter whether 

you are programming 

a software algorithm 

or are involved in 

the field-testing of 

a complex system. 

And then, typically, 

when you are fully 

prepared for every 

conceivable scenario 

and have backups 

for everything, you 

won’t need any of 

your backups because 

your system will just 

work… - Wouter 

to share that fulfillment with your 

team. Similarly for the snowplow 

competition, where we all worked 

to the maximum of our abilities to 

achieve an optimal result. It is a 

great pleasure to see the students 

grow throughout those projects 

and from project to project and see 

them become successful in their 

discipline. 

Will you tell us about some of 

the projects you have worked 

on in the past? 

Frank: Past projects have ranged 

from automatic GPS landing 

systems for airplanes and 

helicopters, to using GPS for aircraft 

attitude and heading determination 

by mounting multiple antennas on 

the airplane, GPS receiver design, 

precision GPS navigation projects 

for aircraft and ground vehicles and 

integration of GPS with numerous 

other navigation sensors. 

Maarten: I have worked on a 

large variety of projects ranging 

from integrity monitors for terrain 

databases used on flight displays on 

the flight deck (so-called synthetic 

vision displays), automatic GPS 

landing systems for airplanes, GPS 

receiver design, laser-based and 

camera-based navigation systems 

for aircraft, unmanned ground 

vehicles and unmanned aerial 

vehicles, alerting and notification 

systems for commercial aircraft 

including collision avoidance 

systems using GPS, and integrated 

system build around inertial sensors 

(accelerometers and gyroscopes). 

Wouter: Since I joined Ohio 

University I have worked on a wide 

variety of projects. We have built a 

GPS/Inertial/Rubidium integrated 

positioning, velocity, attitude, and 


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time truth system that is now used 

on almost all our tests. I have 

consulted NAVTEQ on streamlining 

their process from data collection, 

optimal processing algorithms, to 

map generation. We installed and 

operate GPS ionosphere monitoring 

systems in Alaska, Puerto Rico, 

and Singapore, which has already 

provided some very interesting 

data and subsequent publications. 

I have optimized H-field antennas 

for sub-terrain positioning. And we 

just completed the data delivery 

of a massive data collection effort 

for DARPA where we equipped a 

van with 36 and our DC3 with 24 

different navigation sensors. 

What was your role in the 

projects? 

Frank: For these projects, I was the 

Principal Investigator, but I also 

participated in writing the software, 

soldering circuits, trouble-shooting 

the hardware and digging holes to 

plant antennas in the field. 

Maarten: For most of these projects, 

I was the Principal Investigator; on 

others I was a research engineer. 

In all cases I actively participated 

in the projects and had to write 

software and put hardware together. 

Wouter: On some projects I have 

been the (Co) Principal Investigator, 

on others researcher. My role 

within these projects ranges from 

analytical research to soldering 

circuits, from project management 

to software programming, and 

typically all of the above in the same 

project. 

What was your favorite part of 

the project? 

Frank: To me all phases of a 

project are exciting, starting 

with the concept, design and 

implementation to the operational 

testing and data analyses. 

Maarten: Besides the fact that we 

would look at the problem all the 

way from concept through design 

to implementation and testing of 

the systems, I really do enjoy the 

interaction with my students. Seeing 

them learn and become more 

mature engineers is a delight to see! 

Wouter: It is fantastic if a complex 

project comes together, when 

it actually works after many late 

nights, and when you have a great 

team to share your success with. 

Where was the technology 

used? 

Frank: Most of our projects use 

computers, microcontrollers, Field- 

Programmable Gate Arrays (FPGA), 

analog to digital converters, radio 

frequency front-ends and antennas. 

Maarten: Our projects used 

a large number of electronics 

components including computers, 

RF transmitters and receivers, 

measuring equipment such as 

oscilloscopes, spectrum and 

network analyzers, microcontrollers, 

FPGAs, but also laser scanners, 

cameras, and a large number of 

actual avionics systems (inertial 

navigation systems, air data 

computers, weather radar, radio 

altimeters, GPS receivers, etc.). 

Wouter: We use a wide range of 

equipment. Computers, micro 

controllers, FPGAs, RF antennas, 

filters, amplifiers, mixers, custom 

and commercial RF data collection 

setups, signal generators, spectrum 

analyzers, oscilloscopes, 1-way and 

2-way communication equipment, 

inertial sensors, cameras, laser, IR, 

GPS, etc. 

What were the challenges/ 

successes of the project? 

Frank: For me, the biggest challenge 

of a research project is the planning 

and making sure the project is 

completed before the funding runs 

out. It is difficult to predict when 

the right solutions are invented for 

a particular problem. Nevertheless, 

based on first principles from math 

and physics, the feasibility of a 

particular approach can usually be 

determined. Somehow, everything 

always seems to come together at 

the last minute. 

Maarten: The biggest challenge 

for me was the planning and 

coordination of the work given 

the time frame, available funding, 

available students and engineers 

and collaborators at other institutions 

an din industry. Especially, the 

latter required a considerable 

effort in keeping everybody on 

the same page and getting the job 

done. In terms of actually solving 

the problem, we are always very 

successful in coming up with an 

elegant solution that makes sense 

for the problem. A key to the 

successes has always been to find 

good students and carefully train 

and motivate them so they could 

be very productive on the research 

projects. 

Wouter: The biggest challenge 

is getting everything done in time 

and within budget while balancing 

time and energy among multiple 

projects. 


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Do you have any note-worthy 

engineering experiences? 

Frank: I have been fortunate to work 

on GPS since the early days with 

plenty of “low-hanging” fruit, which 

resulted in the Johannes Kepler 

Award for “sustained and significant 

contributions to satellite navigation,” 

from the Satellite Division of The 

Institute of Navigation, the Colonel 

Thomas L. Thurlow Award for 

“outstanding contribution to the 

science of navigation,” from The 

Institute of Navigation and the 

John Ruth Avionics Award for 

“outstanding lifetime achievement 

in the area of GPS navigation,” 

from the American Institute of 

Aeronautics and Astronautics. 

Maarten: For my work on synthetic 

visions systems and my laser-based 

navigation work, I did receive the 

Institute of Navigation, the Colonel 

Thomas L. Thurlow Award for 

“outstanding contribution to the 

science of navigation.” My work in 

these “new” areas of engineering 

allowed me to do some really 

innovating research. 

Will you tell us about the 

autonomous snow plow 

competition and winning the 

competition for the second 

year in a row 

Frank: For any competition, testing 

is the key to success. For the first 

competition, we were testing 

through the night in the basement 

parking lot of our hotel up until a 

few hours before the competition. 

This year, we realized that lack 

of snowfall was going to limit our 

testing in Ohio, so we contacted Dan 

Morris, director of Ohio University’s 

Bird Ice Arena and he generously 

provided us with snow by scraping 

the ice with his zamboni. We then 

trucked the snow to our test area. 

Sometimes, half of the snow melted 

before we were able to plow it. 

When we arrived in St. Paul, MN, for 

the competition, there was no snow 

either. The competition organizers 

also turned to local ice rinks to 

provide snow for the competition. 

Maarten: Having a solid and welltested 

design with a very good 

user-interface that allowed for 

easy implementations of new robot 

strategies, really made the road 

to this competition much easier. 

Especially, Dr. Wouter Pelgum 

with the help of the students was 

instrumental to this design. This 

made testing much easier and as 

such we were actually ready to go 

before we went to the competition 

instead of having to work late hours 

at the competition. 

Wouter: When we competed the first 

time we pretty much build the robot 

from the ground up which was an 

enormous effort. The first moment 

when we were ready to close the 

control loop was the night before 

the competition. We confiscated an 

underground parking garage and 

worked through the night to fix the 

final bugs and tune the controls. 

For the second competition we were 

in much better shape since we had a 

good robot to start with, but we also 

decided to set our goals significantly 

higher this time. Our robot M.A.C.S. 

had to be much faster (up to 2 m/s), 

more precise (cm-level total system 

error), heavier, and more powerful. 

This required us to rebuild most of 

the mechanics, replace the motors, 

the motor controllers, and optimize 

the software. Furthermore, we spent 

countless hours testing. To test 

the impact of snow loading on the 

controls we extensively tested with 

different amounts of snow, plow 

widths, and plow speeds 


continues to be a 

leader in avionics 

engineering because of 

our faculty and staff, 

our good relationships 

with our sponsors, and 

the fantastic fleet of 

aircraft (and airport 

to go with it) that we 

have to evaluate our 

new technologies. 

This gives us a unique 

edge and insight in 

what it takes to get a 

system on an actual 

aircraft. - Maarten 

while monitoring the robot’s 

telemetry. Prior to the competition 

we replicated the entire competition 

field using snow we trucked in 

from the Ohio University’s Bird Ice 

Arena. This provided us with the 


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most realistic testing environment, 

leaving nothing to chance at the 

competition. All and all this got us 

A highly educated 

workforce is essential 

to stay on top of the 

ever-increasing stateof-the-art 

technology, 

and to remain 

competitive in a global 

market. We need to 

stay focused on quality 

education at the high 

school level, combined 

with creating a 

healthy interest in 

mathematics and 

science, followed 

by excellent but 

affordable higher 

education that 

matches the student’s 

capacities. - Wouter 

in the slightly bizarre situation that 

we didn’t have to change a single 

line of code during the competition, 

nothing to repair, everything just 

worked, leaving us with enough 

time to help out the other teams and 

to jump around in our obnoxious 

yellow suits to entertain the 

audience. 

What are you currently 

working on? 

Frank: I’m working on a variety 

of research programs ranging 

from improved atomic frequency 

references, GPS-based aircraft 

landing systems, camera-based 

navigation, ionospheric studies to 

navigation in space. 

Maarten: I’m working on a variety 

of research programs including 

alerting systems for commercial 

aircraft including GPS-based 

surveillance and collision 

avoidance, laser- and camera-based 

integrated navigation, advanced 

flight displays for the future flight 

deck and navigation, guidance and 

surveillance systems for small-size 

unmanned aerial systems for indoor 

and urban operations (search and 

rescue, etc.). 

Wouter: I am researching the 

possibilities of upgrading the 

Distance Measuring Equipment 

(DME) system to meet the stringent 

demands of next generation 

aviation. With this, we can provide a 

backup in case GPS is not available 

due to, for example, interference. 

Can you tell us more 

about Ohio University and 

the technology they are 

developing? 

Frank: Our Avionics Engineering 

Center provides education for 

the next generation of avionics 

engineers, improves existing 

systems and develops new 

technologies for aircraft and 

spacecraft navigation. 

Maarten: At the Ohio University 

Avionics Engineering Center we 

train the next generation avionics 

engineers and help improve the 

safety and performance of existing 

avionics systems, or design, develop 

and flight test new technologies 

for aircraft and unmanned aerial 

vehicles. Of course, our work 

on navigation system for ground 

vehicles (such as the snow plow) 

provides a fantastic platform for 

the students to get familiar with the 

issues and engineering problems in 

developing a navigation system. 

How does Ohio University 

continue to be a leader in 

avionics engineering? 

Frank: We not only develop new 

technologies, but we also use, 

maintain and upgrade the current 

navigation systems. Key to our 

leadership position is our aircraft 

fleet that includes a King Air 

C90SE, a Douglas Dakota DC-3, a 

L29 Delfin jet trainer, and several 

single-engine aircraft. Our practical 

knowledge of the current problems 

and system limitations enables us 

to develop new technologies that 

can be transitioned into the National 

Airspace System. 

Maarten: Ohio University continues 

to be a leader in avionics engineering 

because of our faculty 

and staff, our good relationships 

with our sponsors, and the fantastic 

fleet of aircraft (and airport to go 

with it) that we have to evaluate our 

new technologies. This gives us a 

unique edge and insight in what it 


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takes to get a system on an actual 

aircraft. 

What direction do you see 

your business/research 

heading in the next few years? 

Frank: Aircraft are becoming 

more autonomous, especially 

with the mandated introduction of 

uninhabited aerial systems (UAS) 

into commercial airspace by Sept. 

30, 2015. To enable additional 

aircraft in the National Airspace 

System, the Federal Aviation 

Administration is pursing what is 

referred to as Performance-Based 

Navigation. 

Maarten: A large focus will be on 

the next generation airspace, air 

traffic management and aircraft. In 

the future we will see a much busier 

airspace with a higher density 

of aircraft including unmanned 

aerial vehicles. This will mean that 

we need to start coming u with 

improvements in a large number 

of areas including the areas where 

we focus our research efforts: 

navigation, surveillance and 

communication. 

What are some new 

technologies we can expect 

to see from Ohio University in 

the near future? 

Frank: We are working on a variety 

of navigation sensors for aircraft and 

UAS to increase airspace capacity 

and safety. 

Maarten: We will be putting a 

lot of efforts in coming up with 

new navigation, surveillance and 

communication systems and their 

user interfaces for the future aerial 

vehicles. 

What challenges do you 

foresee in our industry? 

Frank: The primary challenge I 

foresee for our industry is complexity 

and the challenge of preparing 

the next generation of engineers to 

excel in an environments of rapidly 

increasing knowledge. 

Maarten: One of the challenges 

will be to maintain the avionicsengineering 

work force while 

keeping the quality of the engineers 

the same or even improve it. This 

will require a solid training of 

these new engineers in the various 

electrical engineering programs 

and motivating of high-school 

students to pursue careers in 

electrical engineering. 

Wouter: A highly educated workforce 

is essential to stay on top of 

the ever-increasing state-of-the-art 

technology, and to remain competitive 

in a global market. We need to 

stay focused on quality education 

at the high school level, combined 

with creating a healthy interest in 

mathematics and science, followed 

by excellent but affordable higher 

education that matches the student’s 

capacities. 

What are some of your 

hobbies outside of work and 

design? 

Frank: My wife Janet is a performing 

musician; we both get up every 

morning and wonder how it is possible 

that we are getting paid for 

what we love to do – our jobs are 

our biggest hobbies. Besides our 

work, we enjoy Christian ministries, 

traveling and spending time with 

our family and friends. 

Maarten: My main hobby outside of 

work is music: I do play the saxophone 

and flute and am active in a 

couple of bands. Besides this hobby 

I love to spend time with my family 

(wife and daughter)! 

Wouter: When I’m not working I 

like to do sports. Southeastern Ohio 

is a great place to cycle, and I love 

to push myself to the limit on the 

endless county roads surrounding 

Athens. 

Is there anything that you 

have not accomplished yet, 

that you have your sights on 

accomplishing in the near 

future? 

Frank: My primary goal for the near 

future is to take two of our patented 

research technologies and turn 

them into products, the first is a 

laser-guided aircraft landing system 

and the second is a revolutionary 

GPS receiver design. 

Maarten: Professionally, I have my 

sights set on a couple of goals for 

the near-term. This first is to get my 

work in laser-based navigation and 

vision-based navigation transitioned 

to a small fleet of UAVs. The other is 

to have a real-time flight demonstration 

of my work on altering systems 

on one of our aircraft. Personally, I 

am looking forward to the birth of 

my son in August! 

Wouter: I am currently pursuing a 

grant to extend my DME work to 

provide a steady multi-year funding 

basis for further research and 

development. Furthermore, I hope 

to get tenure soon… On the longer 

term, I am entertaining the plan to 

combine my duties as a Professor 

with commercial activities around 

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Monocular 

Autonomously- 

Controlled 

Snowplow 

INTRODUCTION 

A Monocular Autonomously-Controlled 

Snowplow (M.A.C.S.) was 

designed, implemented and tested 

for participation in the First and 

Second Annual Autonomous Snowplow 

Competitions (ASC) in St. 

Paul, MN in January 2011 and 2012. 

This competition challenges teams 

in the areas of guidance, navigation 

and control (GNC) to develop 

a robot that autonomously removes 

snow from a straight, 1-m wide “I”shaped 

field and a “U”-shaped, 1-m 

wide field that fits inside a 10-by-5 m 

rectangle [1]. 

For the first competition, Ohio University 

assembled a team consisting 

of three undergraduate Electrical 

Engineering students (Samantha 

Craig, Matthew Miltner, Derek 

Fulk) and two faculty advisors. For 

the second competition, the team 

consisted of two undergraduate 

students (Samantha Craig, Ryan 

Kollar), two graduate students 

(Pengfei Duan and Kuangmin Li) 

Figure 1: Monocular Autonomously-Controlled Snowplow (M.A.C.S.) 

and three faculty advisors (Wouter 

Pelgrum, Frank van Graas, Maarten 

Uijt de Haag). An existing robot 

was selected as the basis for the 

snowplow design. This robot was 

designed for challenging Search 

and Rescue (SAR) operations and 


By Samantha Craig, 

Matthew Miltner, 

Derek Fulk, 

Wouter Pelgrum, 

and Frank Van Graas 

features all-electric, four-wheel 

drive using four 1.25-hp motors with 

gearing and wheel encoders [2]. 

Two RoboteQ motor controllers are 

used to establish constant wheel 

rotational velocities for each pair of 

left side and right side wheels. 

EEWeb | Electrical Engineering Community Visit www.eeweb.com 13

PROJECT 

Gyro 

Figure 2: High-Level Block Diagram 

Path 

Planning 

USB 

Commanded 

Position 

Scanning 

Laser 

TCP/IP 

Processor 

SSD: 64GB 

Left Motor 

Controller & 

Encoders 

Following the implementation of 

the design modifications, Figure 

1 shows the current configuration 

of the robot, which was renamed 

to Monocular Autonomously-Controlled 

Snowplow or M.A.C.S. to 

highlight its new mission. 

VEHICLE DESIGN 

USB USB 

Commanded 

Heading 

+ 

Position 

Controller 

+ 

WiFi 

Comm 

- - 

MACS Estimated 

Position 

Position 

Loop 

Laser 

Processing 

TCP/IP 

Right Motor 

Controller & 

Encoders 

Commanded 

Speed 

Relay 

Switch 

Figure 3: M.A.C.S. Control System Block Diagram 

A high-level block diagram of 

M.A.C.S. is provided in Figure 2. At 

Remote 

STOP 

Transmit 

Speed & Acceleration 

limits 

Hdg/Spd 

Controller 

MACS Estimated 

Heading 

Heading 

Loop 

Scanning 

Laser 

Motor Power 

Four 12V 

Batteries 

Left Motor 

Controller 

Right Motor 

Controller 

Heading 

Gyro 

5 Samples/s 

Remote 

STOP 

Receive 

Safety 

Circuitry 

Charging 

Circuitry 

Clean Power 

12V Battery 

Left Wheel 

Encoder 

Wheel 

Speed 

Loop 

Wheel 

Speed 

Loop 

Right Wheel 

Encoder 

100 Samples/s 

MACS 

MACS Heading 

the center of the block diagram is 

an AMD 64-bit, 2.4 GHz Dual-Core 

processor with a 64-GB solid state 

drive (to enable low-temperature 

operations). The processor handles 

all sensor interfacing and data recording. 

Power is divided into clean power 

and motor power. The clean power 

uses a 12-V, 31.6 Ah gel battery, 

while each motor uses two of these 

batteries in series to provide 24 V 

with 31.6 Ah. The safety circuitry 

consists of several relays that must 

all be active at the same time in 

order to enable the motor power 

relay switches. Separate charging 

circuits are implemented for each 

individual battery. When an external 

charging cable is connected to 

M.A.C.S., it automatically disables 

all motor power and proceeds to 

charge the batteries individually by 

switching several relays. 

To protect the processor from the 

environment, a box structure was 

created as part of the top inside 

layer of the robot. 

CONTROL SYSTEM DESIGN 

The control system for M.A.C.S. 

uses three control loops that were 

previously implemented and tested 

on Ohio University’s autonomous 

lawnmower [3]. The control system 

block diagram is shown in Figure 3. 

The three control loops are described 

below: 

1. Constant rotational velocity control 

loop using two RoboteQ 

motor controllers with encoder 

feedback from the front motors. 

The controllers are updated at a 

1000 Hz with a 100-Hz Proportional-Integral-Derivative 

(PID) 

controller. 

2. Heading control loop using an 

XSENS MTi gyro (0.1°/minute 

drift after calibration) at a 50-Hz 

update rate with latencies below 

10 ms. The bandwidth of this 

loop is approximately 10 Hz. 

3. Navigation control loop using a 

SICK LD-OEM1000 scanning 


E-Stop A 

E-Stop B 

External Power 

MACS Position 

FEATURED PROJECT

PROJECT 

laser with passive beacons at 

an update rate of 5 Hz to adjust 

for path deviations. 

The laser position and heading updates 

have a latency of 0.2 second, 

which is acceptable because it is 

corrected using the vehicle speed 

of up to 2 m/s, while unknown crosstrack 

velocities are well below a 

few cm/s, resulting in cross-track 

displacement errors of less than 

2 cm. In practice, the gyro stability 

in combination with the known, 

commanded speed of the robot are 

used to coast the position solution 

to compensate for the laser latency. 

Based on the gyroscope test results, 

cross-track errors are below 1 cm 

after 0.2 s of coasting. 

NAVIGATION 

SYSTEM DESIGN 

The concept for M.A.C.S. is to 

develop a navigation solution for 

dense urban environments that are 

likely GNSS-challenged (building 

blockage, severe multipath and 

interference). The required accuracy 

for the navigation solution is 

5 cm rms. Following a trade study 

that included GNSS, camera and 

laser solutions, the laser positioning 

method was selected as most 

effective and robust to satisfy the 

objectives. The additional benefit of 

the laser scanner is that it provides 

a redundant position solution that is 

calculated every 0.2-second time interval 

following the completion of a 

360° scan. The laser scans in increments 

of 0.25° with a 0.16° beam divergence, 

which provides essentially 

full coverage over the scan range. 

The SICK LD-OEM1000 scanning 

laser was selected, which operates 

at infrared (905 nm) with a ranging 

180 

165 

195 

150 

20 15 10 5 5 10 15 20 360 

210 

135 

225 

120 

240 

Figure 4: Laser returns for a 360° scan 

resolution of 3.9 mm. The laser is 

eye-safe and can be used at distances 

up to 250 m. Figure 4 shows 

an example of one 360° laser scan 

taken with 6 beacons and surrounding 

building structures. 

The laser is at the center of the plot 

in Figure 4. The display range is 20 

meters from center to the outer ring. 

The long, near-solid lines represent 

building structures, while the six 

beacons are identified by arrows. 

GUIDANCE SYSTEM DESIGN 

M.A.C.S. uses several commands 

that are used in a script generated 

to clear the snow of the field. The 

snow field coordinates are used 

to generate command set actions 

that are executed successively as a 

function of the snowplow position. 

The M.A.C.S. command set includes 

the following commands: 

1. Initialize 

2. Idle 

3. Stop immediately 

4. Track heading at a set speed 

(positive or negative) , a set 

acceleration, and a set control 

gain 

5. Turn using a commanded final 

heading at a set speed (for zero 

speed, the robot will have a zero 

turn radius) 

6. Slow stop at a set deceleration 

and a set control gain 


105 

255 

90 

270 

75 

285 

60 

300 

45 

315 

30 

330 

15 

345 

FEATURED PROJECT

PROJECT 

PROCESSOR AND SOFT- 

WARE DESIGN 

As detailed in the System Design 

section, M.A.C.S. uses a single processor 

(AMD 64-bit, 2.4 GHz, Dual- 

Core). The AMD processor runs 

both the high-level and the howlevel 

software. The high-level software 

is written in Matlab® for rapid 

prototyping and to provide an advanced 

development environment. 

High-level functions include laser 

processing, path execution, and 

data storage. The low-level software 

is written in C++ for speed and low 

latency. Low-level functions include 

drivers for the laser, gyroscope and 

motor controllers, and the heading/ 

velocity controller software. Figure 

7 shows the processor timing overview. 

The high-level software runs 

in 0.2-s cycles after the completion 

of each laser scan. 

The low-level software runs in 0.01-s 

cycles after the receipt of new gyroscope 

measurement data. The 

RoboteQ motor controllers update 

every 1 ms, but that functions resides 

inside the motor controller. 

Once M.A.C.S. collects data during 

a test run, all data can be played 

back both in real-time and fast-time 

modes for analysis. This methodology 

is also used after software 

Laser updates 

(High-level on AMD) 

Gyro updates 

(Low-level on AMD) 

Motor updates 

(RoboteQ) 

Figure 5: Processor timing overview 

10 milliseconds 

changes have been made to ensure 

that the navigation solution continues 

to function on all previous data 

sets. 

INNOVATIVE DESIGN 

CONTENT 

M.A.C.S. employs several innovative 

design features to achieve autonomous 

operations for snow removal: 

• Fully functional in GPS-challenged 

environments through 

the use of scanning laser-based 

positioning with unique beacon 

design 

• Fault tolerant laser processing 

that operates in the presence 

of disturbances caused by 

humans or environmental conditions 

• Environmentally-friendly, allelectric 

technology 

• Plug-and-play charging of individual 

batteries with error-proof 

connections 

• Robust traction provided by a 

combination of V-profile snow 

tires, duallies, weight, fourwheel 

drive, acceleration control, 

and optimal plow width 

• Plowing strategy that avoids 

1 millisecond 

200 milliseconds 

snow build-up during turns by 

first backing up and then turning 

• Laser cover to shield it from 

sunlight with stealth mounts that 

do not block or diffract the laser 

beam 

• Matlab® highly flexible development 

environment with TCP/ 

IP and USB interfacing and WiFi 

connectivity, including iPhone 

or iPad remote control and 

status displays 

PRACTICAL APPLICATIONS 

M.A.C.S. was designed to remove 

snow from sidewalks in dense 

urban environments that are likely 

GNSS-challenged due to building 

blockage, severe multipath and/ 

or interference. A practical implementation 

would either use existing 

buildings and objects or laser 

reflectors. Only three features with 

good geometry relative to the laser 

scanner are needed for a redundant 

navigation solution. The laser range 

is 250 m, which supports a cm-level 

accurate navigation solution in most 

if not all urban environments. 

A second, practical application of 

the M.A.C.S. platform is educational 

use for research into challenging 

guidance, navigation and control 

problems. The Matlab® development 

environment in combination 

with flexible TCPIP and USB interfacing 

enables rapid prototyping 

and testing of new concepts. 

EDITOR’S NOTE 

This article was taken from an indepth 

conference paper originally 

published by the Institute of Navigation 

(ION) in September of 2011. 


FEATURED PROJECT

PROJECT 

The full paper is available at the 

ION website [4]. 

REFERENCES 

[1] The First Annual Autonomous 

Snowplow Competition Rulebook, 

Revision 2011.3.0, available 

from: http://www.autosnowplow. 

com/Rulebooks.html (accessed on 

21 January 2011). 

[2] Litter, J. J., “Mobile Robot for 

Search and Rescue,” M.S. Thesis, 

Mechanical Engineering, Ohio University, 

2004. 

[3] Bates, D. and F. van Graas, 

“GPS-Guided Autonomous Lawnmower 

with Scanning Laser Obstacle 

Detection,” Proceedings of 

the Institute of Navigation GNSS-06 

Meeting, Fort Worth, TX, September 

2006. 

[4] Craig, Samantha, Miltner, 

Matthew, Fulk, Derek, 

Pelgrum, Wouter, van Graas, Frank, 

“Monocular Autonmously-Controlled 

Snowplow,” Proceedings 

Figure 6: Monocular Autonomously-Controlled Snowplow Team 

of the 24th International Technical 

Meeting of Satellite Division of the 

Institute of Navigation (ION GNSS 

2011), Portland, OR, September 


Electrical Engineering Community 

Contact Us For Advertising Opportunities 

1.800.574.2791 

advertising@eeweb.com 

www.eeweb.com/advertising 

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TECHNICAL ARTICLE 

Today’s embedded developers 

look for hardware and software 

solutions that enable them to 

respond quickly and easily to 

customer and market demands, 

last-minute design changes and 

competitive challenges. Of all the 

components in a typical embedded 

system, the microcontroller (MCU) 

should provide the developer 

with the utmost in versatility and 

configurability, enabling them to 

implement new system features 

easily and efficiently through 

firmware updates and I/O changes. 

Think “Swiss Army knife” etched in 

CMOS. 

However, with many conventional 

MCU architectures, even minor 

I/O changes can cause headaches 

for developers engaged in printed 

circuit board (PCB) design, 

especially for cost- and spaceconstrained 

embedded systems. 

For example, the connectors in the 

system might all be on one side 

of the enclosure. The problem is, 

though, some of the I/Os may need 

to be routed to the opposite side of 

the MCU by passing underneath 

it because the MCU supplier has 

defined the pinout in such a way that 

the I/O connections for the revised 

system cannot all reside on one 

side of the IC. The rearrangement 

of pins used for a given combination 

of I/O functions may force the PCB 

layout engineer to move to a higher 

number of board layers, thus 

increasing the cost and complexity 

of the overall system. 

An additional design challenge 

concerns the MCU package 

itself. To reduce cost, some MCU 

suppliers may provide versions 

of a device that share functions 

between pins and thus squeeze the 

IC into a smaller, cheaper package. 

Register configurations provide the 

ability to allocate those I/O pins to 

a selection of different peripherals, 

but the degree of freedom is usually 

limited; the configuration-control 

hardware may support only one or 

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vendor did not anticipate. The wide 

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MCUs, Silicon Labs 

has implemented a flexible I/O 

system into the design of its new 


TECHNICAL ARTICLE


ARM® Cortex-M3 core-based 

Precision32 MCUs. The key to 

the design is a highly configurable 

dual-crossbar architecture: a 

programmable switching matrix 

that enables a developer to route 

an input to any one of a number of 

output pins. 

The Precision32 MCU architecture 

defines two crossbars (one for 

either side of the IC) that can link 

any internal I/O function to a wide 

range of pins, as Figure 1 illustrates. 

In this example, which uses a TQFP- 

80 package, Crossbar 1 connects to 

pins 9 through 40, excluding only 

28 and 29, which are power and 

ground pins. Crossbar 1 supports 

14 different internal functions, 

including various serial ports, 

timers, and comparators; any of 

these functions can connect to any 

of the external pins that the crossbar 

serves. Some of these pins can also 

be mapped to A/D converter inputs 

or 5V-tolerant outputs. 

The crossbar architecture provides 

the designer with a number of 

benefits. The architecture makes 

it possible to arrange the pinout of 

the chip to simplify board design, 

placing a group of I/O pins as close 

as possible to the ICs or connectors 

to which they need to be linked. 

This approach can often save cost 

by allowing the use of a PCB with 

fewer routing layers as it avoids 

the need to route underneath the 

MCU or take many circuit traces 

through a congested area of the 

PCB. And it can improve signal 

integrity as sensitive traces can be 

kept as short as possible or routed 

close to ground lines. Furthermore, 

pinout changes can be made easily 

– simply by reprogramming the 

1 

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40 

KEY 

USART0 

PCA0 

CMP0 

UART0 

SSG 

RTC 

I25 

I2C1 

CROSSBAR 0 

registers that control the crossbar – 

to accommodate last-minute board 

changes. 

Such fine-grained control over I/O 

configuration makes it much easier 

for designers to use a more costeffective 

package, choosing which 

functions to connect to pins and 

which ones to leave unconnected. 

To allow easy migration from other 

MCUs, Silicon Labs chose the 

ARM Cortex-M3 as the processor 

core for the Precision32 family. This 

processor core has rapidly become 

a de facto standard in 32-bit MCU 

architectures thanks to its broad 

adoption in the embedded market 

by a wide variety of MCU suppliers 

and software tool vendors, 

providing a high degree of choice 

for the embedded developer. It 

has widespread support among 

software companies in terms of 

conventional development tools 

such as C and C++ compilers 

and real-time operating systems. 

Standardization on ARM cores has 

now made it easier than ever to 

port code from one 32-bit MCU to 

another. As a result, the deciding 

factor in MCU selection is shifting 

from the CPU core architecture to 

the peripheral set and th innovative 

ways in which MCU vendors 

address system-design issues. 

A flexible crossbar is easier to 

understand than many of the ad 

hoc I/O remapping schemes used 

by other MCU vendors. To further 

improve ease of use, Silicon Labs 

provides a complimentary software 

tool that simplifies the task of 

device configuration. Silicon Labs’ 

AppBuilder tool offers a graphical 

interface that allows designers to 

drag-and-drop functions to pins. 

Once the configuration is complete, 

the tool generates the boot code 

required to load this configuration 

into the MCU. This tool works with 

commercial IDEs including Keil 

and IAR as well as the popular 

Eclipse development environment, 

which Silicon Labs has adopted and 

modified to support Precision32 


SPI0 

PCA1 

CMP1 

UART1 

USART1 

I25 

Timer 0 

SPI1 

CROSSBAR 1 

CMP0S 

SPI2 

I2C0 

PB 

Peripheral on 2 Xbars 

GPIO on crossbar 

CMP1S 

USART1 

UART1 

6-ch PCA 

I250 

Timer 1 

SPI2 

SPI1 

UART0 

LPTimer 

GPIO off crossbar 

Power / GND 

Test and Regulator 

60 

59 

58 

57 

56 

55 

54 

53 

52 

51 

50 

49 

48 

47 

46 

45 

44 

43 

42 

41 

Figure 1: Precision32 

MCU Dual-Crossbar 

Architecture 

TECHNICAL ARTICLE


Figure 2: Precision32 AppBuilder Tool 

products. 

The AppBuilder tool (see Figure 2) 

goes further: enabling developers 

to quickly and graphically choose 

peripheral mix, select peripheral 

properties, set up clocking modes 

and customize pin-out, all without 

reading the data sheet. The IDE 

support also goes further in terms 

of MCU support by providing 

direct support for all members of 

the Precision32 MCU family. The 

Precision32 dashboard provides 

the latest documentation, code 

examples and software all in one 

place, removing the need to hunt 

down register locations and driver 

source code in data sheets and 

applications notes. 

Support for peripherals is augmented 

by the inclusion of Cortex 

Microcontroller Software Interface 

Standard (CMSIS) compliant 

code. CMSIS provides an interface 

for common peripherals that enables 

peripheral driver re-use and 

simple porting from other ARM- 

based MCUs. On 

top of this, Silicon 

Labs has implementedmiddleware 

designed 

to make writing 

code for multitasking 

and data 

transfers simple. 

This provides important 

support 

for complex systems 

that need, 

for example, USB 

support. There 

are many configuration 

options and 

usage models for 

USB. Silicon Labs 

has used its longstanding 

experience with USB to 

provide a rich suite of middleware 

functions that ease the job of implementation. 

Given the number 

of applications that now demand 

USB support, from sports watches 

to data loggers, engineers need to 

get up to speed on USB as quickly 

as possible, and this library makes 

it possible. For example, to create 

USB-to-UART transfers, developers 

simply specify properties such 

as USB transfer type, data size, 

and synchronous or asynchronous 

UART operation. 

The library provides a number 

of USB class drivers, including 

audio, human-interface device, 

mass storage and device firmware 

update (DFU) libraries for easy 

development. 

In common with the strategy of 

providing a 32-bit MCU family 

that supports the cost-, time- and 

space-constrained demands of 

today’s systems, the USB hardware 

itself was designed for maximum 

utility with the minimum number 

of external support components. 

Many on-chip USB controllers are 

not feature complete, demanding 

components such as external clock 

generators. The USB controller 

on the Precision32 MCU family 

devices has its own integrated 

precision oscillator, using a novel 

clock-recovery technique to 

achieve 0.25 percent accuracy 

without an external crystal. The rest 

of the MCU can use this oscillator 

or a separate one – allowing greater 

flexibility over clocking regimes in 

low-power modes – that is either 

fed by a low-cost 32 kHz crystal or 

can run in open-loop mode. This 

novel approach enables members 

of the Precision32 MCU family to 

operate without the need for a costly 

external crystal. 

Similarly, the internal voltage 

regulator of a Precision32 MCU 

eliminates the need for an external 

regulator. The MCU can operate 

directly from a 5V supply, allowing 

it to be powered directly from USB 

or a separate unregulated source. 

This regulator can also drive an 

output rail at a programmable 

output voltage, enabling the MCU 

to provide power to additional ICs 

while still avoiding the need for an 

external regulator. Alternatively, this 

output can act as a constant current 

source to drive the backlight on an 

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Similar care has been taken in the 

implementation of other analog 

and digital peripherals. The A/D 

converter, for example, provides 

12-bit resolution. In addition, all of 

the Precision32 analog peripherals 

are tested and specified across 


TECHNICAL ARTICLE


temperature and voltage. Many 

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Configurability extends to the analog 

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The analog comparators have 

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EFFICIENCY (%) 

90 

85 

80 

75 

70 

0 1 2 3 4 5 6 7 8 9 

LOAD CURRENT (A) 

FIGURE 1. EFFICIENCY 5V INPUT TO 2.5V OUTPUT, T A = +25°C 

April 5, 2012 

FN8264.1 

10 11 12 

Features 

• DLA SMD#5962-12202 

• 12A Output Current for a Single Device (at TJ = +150°C) 

• 19A Output Current for Two Paralleled Devices 

• 1MHz or 500kHz Switching Frequency 

• 3V to 5.5V Supply Voltage Range 

• ±1% Ref. Voltage (Line, Load, Temp. & Rad.) 

• Pre-Biased Load Compatible 

• Redundancy/Junction Isolation: Exceptional SET Performance 

• Excellent Transient Response 

• High Efficiency > 90% 

• Two ISL70002SEH Synchronization, Inverted-Phase 

• Comparator Input for Enable and Power-Good 

• Adjustable Analog Soft-Start 

• Input Undervoltage, Output Undervoltage and Adjustable 

Output Overcurrent Protection 

• QML Qualified per MIL-PRF-38535 

• Full Mil-Temp Range Operation (-55°C to +125°C) 

• Radiation Environment 

- High Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 krad(Si) 

- ELDRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100 krad(Si)* 

*Level guaranteed by characterization; “EH” version is 

production tested to 50 krad(Si). 

• SEE Hardness 

- SEL and SEB LETTH . . . . . . . . . . . . . . . . . . 86.4MeV/mg/cm2 - SEFI LETTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43MeV/mg/cm2 - SET LETTH . . . . . . . . . . . . . . . . . . . . . . . . . . 86.4MeV/mg/cm2 AMPLITUDE (V) 

25 

20 

15 

10 

5 

0 

Get the Datasheet and Order Samples 

http://www.intersil.com 

CH1 MASTER LX + 20V 

CH2 SLAVE LX + 15V 

CH3 VOUT x 10 

CH4 SYNC 

-6 -4 -2 0 2 4 6 8 10 12 14 

TIME (µs) 

FIGURE 2. 2-PHASE SET PERFORMANCE at 86.4MeV/mg/cm 2 

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2012 

All Rights Reserved. All other trademarks mentioned are the property of their respective owners.

State Machine 

Heretic 


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Like many of you, it’s been drilled into me 

by the Reuse Methodology Manual to write 

my state machines in VHDL as a pair of 

processes: a combinatorial process to compute 

the next state from the inputs and current state, 

and a sequential process to update the current 

state with the next state. 

Here’s a simple example of that format: a state machine 

that simply increments the counter state variable 

whenever the enable input is asserted: 

comb: process(cnt_r, en_i) 

begin 

if en_i = ‘1’ then 

cnt_x


1 

2 

3 

4 

5 

6 

Because cnt_x has no explicit assignment if the enable 

is not asserted, the synthesizer will make it into a latch. 

That’s usually not what you want, especially in your 

supposedly combinatorial process. To avoid latches, I 

usually put a default assignment for each state variable 

right at the top of the combinatorial process: 

The default assignment keeps the counter at its current 

value. This will be overridden in the code that follows 

if the enable is asserted. Either way, the state variable 

always has an explicit assignment and an inferred latch 

is avoided. 

Too much code: 

Two processes, twice as many signals, long sensitivity 

lists and default assignments all serve to increase the 

amount of code you have to write, debug, maintain and 

document. And more code means that less of the total 

design fits on the monitor screen, which makes it harder 

to “load the design into your head” and increases your 

chances of making an error. 

Because of the “code bloat” problem, lately I’ve been 

writing my state machines as a single process: 

1 

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3 

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5 

6 

7 

8 

1 

2 

3 

4 

5 

6 

7 

bad comb: process(cnt_r, en_i) 

begin 

if en_i = ‘1’ then 

cnt_x


Figure 1 

A 

do_it 

done_it B 

clk 

do_it 

done_it 

clk 

B to perform the operation repeatedly, it would have to 

go through a multiple-cycle handshake to initiate each 

operation, rather than just being able to assert and hold 

the request signal. 

A two-process state machine offers a better solution in this 

case. The combinatorial process of A could immediately 

respond to B’s done_it signal and lower the do_it signal 

before the next clock edge. A could also keep the do_it 

signal continuously asserted if it wanted B to do multiple 

operations. 

In the end, which type of state machine should be used? 

I find myself using one-process state machines where I 

can, and the two-process type where I need more control 

to achieve performance. I know that doesn’t hew to the 

guidelines espoused in the RMM, but I’m an engineer so 

I’ll take the liberty to use my own judgment and leave the 

cookbook approaches to the robots. 

[Aside: If you want to see an even more heretical way 

to code state machines, check out the inferred state 

machines Martin Thompson talks about in his blog. ] 

About the Author 

1 2 3 4 5 

David E. Vandenbout earned a B.S.E.E. degree from 

North Carolina State University (NCSU) in 1978 and an 

M.S.E.E. from M.I.T. in 1979. He worked as a Member 

of Technical Staff at Bell Telephone Laboratories from 

1978-1983 until they suggested he explore other career 

clk 

Figure 2 

opportunities. He completed his Ph.D. at NCSU in 

1987 and worked there as an Assistant Professor doing 

research in the areas of neural networks, statistical 

physics, computer tomography, and FPGA-based rapidprototyping. 

After publishing over 45 journal articles, 

conference papers and book chapters, he left in 1993 

due to an allergic reaction to the passive voice. In 1990, 

he was one of the founders of X Engineering Software 

Systems Corp. (XESS), a company that originally 

developed software for X11-based scientific workstations 

until they found out nobody actually wanted to pay 

any money for that. He re-directed XESS so that it now 

develops and sells low-cost, open-source, FPGA-based 

hardware. XESS has developed and delivered boards to 

thousands of individuals and hundreds of corporations 

and universities in almost every country in the world (still 

waiting on Antarctica). XESS FPGA boards have been 

used in everything from classroom instruction to digital 

video processing to cracking the cryptographic codes of 

the SpeedPass system. ■ 


A 

comb 

clk 

do_it 

done_it 

clk 

A 

comb 

do_it 

done_it 

1 2 3 4 5 

B 

clk 

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