25.4.6 Direct Current Power

The power of electricity is called electric power. The electric power is equal to the value of multiplying a voltage by a current. Electric power means the amount of energy consumed when a current goes through a resistance. The electric power is expressed in W (Watt).

The electric power at direct current is calculated as follows.

Electric Power = Voltage × Current ( P = VI )

25.4.5 Pull-up Resistor and Pull-down Resistor

In many electronic circuits, it is the pull-up resistor and pull-down resistor that are used as one of the methods to safely protect the circuit from being broken down from various electrical shocks and to ensure that it can operates correctly according to the originally designed intention under any circumstances. Basically, the pull-up resistor and pull-down resistor are a term defined by where to equip the resistor between power supply and ground, and allow a small current to flow by using a resistor of appropriate size for each resistor. Next, we will explain this.

25.4.4 Kirchhoff’s Laws

Kirchhoff’s law has a first law of current and a second law of voltage.

25.4.4.1 First Law – The Law of Current

The first rule is that on a certain path of current, the sum of incoming currents and the sum of outgoing currents is the same. That is, the sum of the current flowing into one point of the circuit and the current flowing out of the point is the same.

25.4.3 Series and Parallel of Power

There are three ways of connecting the power supply: series connection, parallel connection and series/parallel connection.

25.4.3.1 Series Connection

The way to connect a (+) pole of one cell to a (-) pole of another is series connection. At this time, the total electromotive force is the sum of the electromotive force of all the batteries.

25.4.2 Series and Parallel of Resistance

Basic resistance connections include a series connection where the combined resistance increases and a parallel connection where the combined resistance is reduced.There are three ways of connecting resistance: series connection, parallel connection and series/parallel connection.

25.4.2.1 Series Connection of Resistance

● Combined resistance of series connection

25.4 Basics of Electronic Circuit

Here, we will explain the basic knowledge of electronic circuit.

25.4.1 Short and Resistance

Short is also generally referred to as a short circuit, which means that two wires with different potentials are directly connected to each other, such as connecting a (+) wire and a (-) wire without a resistor in a circuit where electricity is supplied. When this direct connection is made, excessive current flows for a moment and spark occurs.

25.3 Basics of Electricity/Electronics

Here, we will explain the basics of electricity and electronics.

If you need additional information, please refer to the following:

■ http://portal.hrd.go.kr/EL/contents/084/01/ch01_02.htm

■ http://cafe.daum.net/kneeng

■ http://blog.daum.net/hongbkim/2542

■ http://blog.naver.com/dhjdhj11/150184044066

25.2.3 Precautions and Features in Using GPIO

● Precautions in using GPIO pin

■ When powering Raspberry Pi, make sure that metal object does not touch the GPIO pin.

■ Do not supply more than total 250mA current from 5V power pin.

■ Do not supply more than total 50mA current from 3.3V power pin.

■ Do not supply higher than 3.3V to all GPIO pins at the input.

■ Do not use more than 3mA current per pin at the output.

■ Do not supply higher than 5V power to Raspberry Pi.

25.2.2 GPIO Port Details

25.2.2.1 GPIO Basics

There are various kinds of GPIO interface pins in Raspberry Pi. Each pin has its own purpose, and several pins are used together to make a specific circuit.

● DNC (Do Not Connect )