R5 Resistor: The stripes are in orange-orange-red color order, which indicates a 3.3K resistor. This resistor is used to improve the high current capability of the boost converter chip. Something to note about this resistor, and all resistors in general, is that they are non-polar, which means they can be inserted any way into the circuit board. You don’t have to worry about putting it in “backwards”.
R2 and R4 Resistors: These resistors have the pattern Violet Green Black Red Brown, which means that they are 75K 1% resistors. These resistors are used to figure out what kind of charger is connected.
R1 and R3 Resistors: These resistors have a Yellow White White Red Brown pattern, which indicates that they are 49.9K 1% resistors. These resistors serve the same purpose as the R2 and R4 Resistors, which is figuring out what kind of charger is connected. The only difference between these two are their size and their color pattern.
C1 and C2 Capacitors: These ceramic capacitors are also non-polar, so they can be placed into the circuit board in any orientation. The capacitor in the C1 slot is responsible for stabilizing the output voltage, and filters out high frequency noise so that the 5V output is nice and smooth. The C2 capacitor is used to stabilize the internal reference of the boost converter chip. This keeps the chip stable so that it will generate a voltage as precise as possible.
D1 Diode: This diode is used to ensure that energy is transferred from the batteries to USB port, and not the other way around. Diodes have a special property that allows current to flow only one way, and because of this, the diode has to be inserted in a certain way into the circuit board, and is not non-polar.
IC Socket: This socket protects the boost converter chip and ensures that the boost converter chip can be replaced. It is placed over the resistor in the R5 slot.
L1 Power Inductor: This component is used by the DC/DC converter chip to store and convert power from low voltages to high voltages. Inductors are just a coil of wire, so they have no polarity, and can be placed either way.
C3 and C4 Electrolytic Capacitors: The two electrolytic capacitors placed in the C3 and C4 slots help smooth both the input and output voltages, to keep them stable during the up-conversion. They are used for low frequency noise, and are often paired with a ceramic capacitor. Electrolytic capacitors are polarized and must be placed correctly or the circuit will not work. The longer wire is the positive one and must be placed in the positive hole in the circuit board, and the shorter one is meant for the negative hole.
Boost converter chip: This chip is responsible for upping the voltage in the system while lowering current. It is inserted into the IC Socket, and is not soldered on to the circuit board, so that it can be replaced.
Battery holder: Contains two double a batteries and supplies their power through red and black cables that are soldered onto the circuit board.
USB port: A USB-A charging cable can be inserted into this port and power can be drawn to the connected cable/device from the system.