Trying
to wrap my head around electronics is surprisingly similar to trying
to sew a complicated pattern with a sewing machine. In sewing you
need to think about the order of everything, measurements, ratios,
materials like the fabric and lining and reinforcement and buttons...
I could go on. I never really got into sewing the way my mom did.
Electronics also seems to require holding a lot in your head at once.
I am
really starting from scratch here.
I
found out that in first designing a circuit, you use what is called a
“solderless breadboard,” pictured below:
Underneath
a breadboard, there are rows of metal strips. On top, there are holes
which you can plug a wire into. If you plug two wires into the same
row of holes, they become connected, because they both touch the same
metal piece. If you want to connect 5 wires together, you just plug
all 5 wires into the same breadboard row.
The Arduino come in where if you have two servos, you need to connect 6
wires (2 signal wires, 2 power wires, 2 ground wires). The Arduino
has only 1 power pin, and you might not want to shove two wires into
the same pin if the wire is too thick. Instead, you would connect one
end of one wire to the Arduino power pin, and the other end of the
same wire into a breadboard row. That gives you 4 holes left in the
same row, into which you can plug a servo power wire. You can do the
same for ground.
Then,
when I want to program the servos, in order to tell them to calculate
the angle, the Arduino software program has a built-in library for
servos. The library is basically a way to use simple words like
write(56) to mean much more complicated things, like "calculate
the angle to make the servo go to 56, then send that signal to the
servo”.
So
instead of calculating the necessary angles yourself, the library
does the heavy code stuff for you. All I have to do is give the
angle.
At
the end of the code in the tutorial below there's a code example:
arduino.cc
Then,
to just get my servo running, all I need to do is copy and paste that
into the Arduino program and hit upload. This code makes my servo
sweep back and forth between 0 and 180 degrees. (In this coding
program, everything after // is a comment. The Arduino doesnt know
these comments exist, so I can write anything I want. They're helpful
for showing other programmers, and future me, my thought process
while coding).
The
brackets move based on instructions from the code myservo.write(pos),
which is the actual piece of code that makes the servo turn. So if I
just write myservo.write(56);, the servo will spin to 56 degrees and
stay there until I send another instruction.
By
the way, a servo is used when you need to spin something precisely. A
regular motor spins as fast as it can whenever you give it power, but
the problem is you never know exactly how far the motor has spun.
Therefore, a servo has a special chip inside that can sense how far
the servo motor has spun, and based on that can calculate the angle
of whatever is attached to the servo motor.
The
servo has 3 wires: power, signal, and ground. This chip listens for
instructions sent to it over the signal line. Once it receives an
instruction to spin to a certain angle, it takes care of the math
needed to spin the motor a precise amount, then stops the motor
itself once the angle has been reached, and waits for further
instructions.
So
where is the instruction coming from? What does that consist of?
Well, it cannot spin on its own, its just a smart motor really, so it
needs a brain, like an Arduino, to tell it where to turn to!
When
I write myservo.write(56); , the Arduino looks up what that means in
the servo library (which it knows is being used because of the
#include Servo.h instruction at the top of the code). The servo.h
library then translates the angle provided into the instruction
that's to be sent to the servo, and then passes that information
along (in this example pin 9, which is where the servo's signal line
is connected). The signal itself is in the form of a pulse wave,
meaning it's a very quick pulse of energy. The longer the pulse, the
greater the angle requested from the servo.
I'm
not certain of the specific pulse widths, but it's something like: a
10ms pulse would turn the servo to 10 degrees, and 100ms would turn
the servo to 100 degree.
It's
based on both the amount of energy collected from the solar panel and
the angle of the sun.
The
amount of energy coming in is equal to the optimal sun angle.
Therefore, when we're at the optimal angle, we're collecting the
largest amount of energy.
The
basic flow of the program will be:
The
Arduino tells the servo to spin to degree 1
The
Arduino writes down the amount of energy collected at degree 1
The
Arduino tells the servo to stop at each angle from 2-180, taking a
measurement at each degree of solar energy
Once
all the data has been collected, the Arduino chooses the angle at
which is detected the most amount of energy, and tells the servo to
go to that angle and stay there
Then
it stays at that angle until it senses that the amount of energy
coming in has dropped
Then
repeats the cycle to find the new optimum angle
It's
not actually going to move that much because if it goes to far it
will sense a drop in energy coming in. The servos will be attached to
the solar cell, and they will use it to move it about. As long as the
bottom of the pan/tilt bracket is anchored in something heavier than
the panel, it should work (Spolier alert: the panel IS to heavy and
we still need to fix the problem).
The
Sunny Buddy is smart enough to be able to charge the battery while
something is plugged in.
learn.sparkfun.com
The
pads that are labeled Load are where we'll be soldering the
usb jack. All we have to so is solder the + to the + side of the usb
jack, - to -, and away we go.
The
LiPower Boost converter is needed because the battery only outputs
3.7V. Therefore, if you measured the voltage at the Load pads,
you'd only see the voltage coming out of the battery, which is ~3.7V.
We need to step this up to 5V so we can charge over USB, which
expects 5V. The LiPower is what holds the charge and releases it to
increase the voltage.
Therefore,
the connection will be: Sunny Buddy → battery → LiPower → USB
By
using an inductor, the LiPower Boost converter can build a magnetic
charge within itself and by carefully timing the pulses going into
the inductor, it can step up the voltage leaving the inductor.
The
solar panel plugs into the sunny buddy, which handles the conversion
from solar energy into battery charging energy.
The
ideal place for adding cable length is tricky to figure out--we'll
have to do some calculations.
The
Arduino and servos will hook up to for power the LiPower output as
well, same 5V place as the USB jack. We're supposed to use
power-saving techniques to reduce the amount of power they actually
use.
*Next* we'll talk more about programming the servos and using LCD Shield to help us make sure that the Arduino is performing correctly.
