A circuit is a loop
in which electrical current - or the flow of electrons - can travel. A circuit
must be closed in order to operate. The three important things to know about a
circuit are voltage, current, and resistance. Voltage is a source of electric
potential, or a difference in charge, that drives the circuit. It is measured
in volts (V). Current is rate at which electrons move throughout a circuit. It
is measured in Coulombs (charge, C) per second, or Amperes (Amps, A).
Resistance affects the rate of electron flow, making it more difficult for
electrons to pass through a specific area and therefore decreases the current.
It is measured in ohms (Ω). These three are related in the following equation:
V=IR, where V is electric potential or voltage, I is current, and R is
resistance.
Too high of a
current can both be physically dangerous and break electrical components, so
devices called resistors implemented in the circuit. Resistors are labeled with
four to five different colored stripes to indicate their number of ohms. Figure
1 below shows the standardized color codes in a graphic from the Elegoo Super Starter Kit manual.
Figure 1.
Light emitting
diodes (LEDs) are sources of light that are easy to use in basic electrical
circuits. They typically require to be connected with a 220-ohm resistor in
order to operate properly. If a resistor is not connected in the circuit, the
LED will burn out. LEDs come in a variety of colors, including specialized LEDs
that can be programmed to change colors. These LEDs are called RGBs, as they
can be red, green, blue, or a combination of these three colors. RGBs require
three separate connections to power: one for red, green, and blue. Each
connection requires its own resistor.
Circuits can be built and tested temporarily in a breadboard. A breadboard is a board with a bunch of small holes in it, built specifically for making electrical connections. There are connections underneath the board that complete the circuit, shown in the below figure 2. The blue represents the ground connection and the red the power. Various electronic components can be plugged into the holes to connect in either series (in a row) or parallel (separately, but with a common start/end). Breadboards allow circuits to be tested without having to solder (melt metal to make more permanent connections) them in place.
Figure 2.
This project uses an
Arduino UNO to drive the circuit. An Arduino UNO is a microcontroller. It is essentially a
mini computer on one circuit board about the size of the palm of your hand. It
can be plugged into a computer to program whatever circuit is connected to it.
Arduino is open source, which means other companies can use and modify it and
make their own version. The group will be using an Elegoo UNO board instead of
an official Arduino board because it is cheaper. However, the two boards serve
the same function and operate through the same official Arduino Integrated Development Environment (IDE).
Figure 3.
Figure 2 shows a graphic from Tinkercad for circuits of an Arduino UNO. As labeled on the
board, there are both digital and analog ports. Digital ports are best used for
plugging in things that can only be turned on or off. Analog ports can be used
to vary the voltage to the ports. For example, an LED plugged into a digital
port can only be turned on, or set to HIGH, or off, set to LOW. If it were
plugged into an analog port, its brightness or intensity can be varied.
