In the process of writing this article,
I was asked why we didn’t use linear
actuators. To tell the truth, we
hadn’t even considered it. A rotary
actuator with spur and pinion gears
requires constant power to hold a
fixed position, whereas a linear
actuator with a screw or worm gear
can hold its position without being energized — thereby
consuming less power. Linear actuators might have been a
(Figure 8). Whenever my mind was free to wander
throughout the day, I thought about this project. I rolled
ideas round and round in my head, contemplating my
designs from every conceivable angle. I was looking for
flaws and trying to figure out the order of construction.
Anyone who has ever designed a complicated machine
knows that the order of construction must be strategically
planned — lest you make a permanent, irreversible move
only to realize that you should have done something else
first. It’s agonizing, yet euphoric at the same time! It is
creation, and it is wonderful; there is no better feeling!
THE MOMENT OF TRUTH
The three of us stayed up the entire night before the
big presentation. An erroneous line of PBasic code pushed
one of our servos beyond its mechanical limits, stripping
the gears inside. Mike and I had to drive an hour away to
pick up a replacement servo while Adam furiously rushed
to complete the computer code. When we finally finished
the solar tracker — just an hour before the presentation —
we were exhausted! After showers and a quick change
of clothes, we made a mad dash for the engineering
There we stood in front of a classroom full of
professors and fellow students, waiting to be judged. It
was the moment of truth, the culmination of seven
months of hard work — and supposedly the crowning
achievement of our college educations. We each took
turns telling about the different aspects of the project, all
the while wondering if it would work at the crucial
moment. Then, with mounting tension and nervous
trepidation, I flicked on the power switch! For a moment,
there was nothing but silence as the entire room looked
on in wide-eyed anticipation. Then suddenly, as all the air
in the room seemed to be sucked up in one collective
gasp, it jerked to life and smoothly positioned itself toward
the light source (an incandescent flood lamp). It worked!!!
I think that Adam, Mike, and I were just as shocked as
We received many questions and compliments.
Though bulky, heavy, and not nearly as efficient as it
could have been, it worked! We each received an A in the
course. When Dr. Goodman told me that this solar tracker
was the quintessential Senior Design project, I felt that all
The numbers that we use every day (0 - 9 or some combination thereof) are part of the decimal number system. Computers use
the binary number system (0 and 1) because their transistor logic gates have two states: off and on. Computers represent decimal
numbers as a string of zeros and ones.
Say, for example, that one of the Bug Eye’s light sensor voltage divider circuits is measuring 2.7 volts. The microprocessor
(BS2p40) doesn’t understand 2s and 7s, only 0s and 1s. So, the analog voltage (2.7V) has to be converted to a binary (or digital)
representation for the computer to understand.
Here’s how to make the conversion yourself: That’s 2.7 volts out of a maximum five volt reference; 2.7 divided by 5 equals 0.54
or 54%. Since we used eight-bit analog-to-digital converters, that means that the resolution of the binary value is 2^ 8 or
2x2x2x2x2x2x2x2 or 256 (values 0 - 255). Now, 54% of 256 is 138, but we say 137 since we’re starting at 0 instead of 1.
So, now we have a prorated value of 137 out of 256 (the same ratio as 2.7 out of 5). Next, we represent the decimal number
137 in binary form; 137 in decimal equals 10001001 in binary. Notice the decending powers of two below.
(2^ 7)x1 + (2^ 6)x0 + (2^ 5)x0 + (2^ 4)x0 + (2^ 3)x1 + (2^2)x0 + (2^1)x0 + (2^0)x1 = 137
(128)x1 + ( 64)x0 + ( 32)x0 + ( 16)x0 + ( 8)x1 + ( 4)x0 + (2)x0 + (1)x1 = 137
(128)x1 + 0 + 0 + 0 + ( 8)x1 + 0 + 0 + (1)x1 = 137
128 +0 +0 +0 + 8 +0 +0 +1 =137
128 + 8 + 1 = 137
10001001 (binary) = 137 (decimal)
Therefore, the microprocessor now understands 10001001 to mean 2.7 volts (or a little more than half of the five volt reference) is
being measured by that particular light sensor. After polling the other 15 light sensor circuits, the computer can compare the binary
representations of those voltages and decide which three are seeing the most light — and therefore determine in which direction the
sun is located.