# Ohm Law, Symbol of Resistor, Types, and Defenition

Symbol of Resistor - In electronic devices, if you have ever seen a component like the picture below, its name is Resistor. But resistors are not just like the following picture, there are many versions, you will read the article below.

This component is the most basic component and Symbol of Resistor that you must know if you want to play in the field of electronics, because it will be very widely used.

## Definition of Resistor

Resistor is a passive component to reduce current flowing in an electrical circuit. Resistor comes from the word "Resist" which means to reduce, hold, block, reject or inhibit.

The ability of a resistor to carry current is called resistance.

We can analogize that electric current is like water. While the resistor is a water pipe.

When water flows in a clean pipe, the amount of water entering is equal to the water leaving. However, if the pipe is dirty inside, has a lot of moss or there are lumps of soil, then the amount of water that enters is not the same as the water that comes out.

Well, the pipe was also called the Resist component, because it has blocked the flow of water with the presence of moss and lumps of soil. The amount of the resistor's ability to block electric current, depends on the resistance value.

The greater the resistance value, the greater the ability to inhibit electric current. Resistors are called passive components because these resistors do not require an energy source from other components to be able to inhibit electric current.

### Symbol of Resistor

Resistor symbols such as jagged or zigzag are American and Japanese standard resistor symbols often known as ANSI (American National Standards Institute), while square is a European standard and is often known as IEC (International Electrotechnical Commission). Some Symbol of Resistor are as follows:

### Ohm's Law and Units

The unit value of this resistor is “Ohm”. The current flowing in the resistor (A) is equal to the voltage across the resistor (V) divided by the resistance (R).

I = V / R

While the power consumption (P) of a resistor is equal to the current flowing (I) times the voltage across the resistor (V).

P = I x V

Using another formula, the power consumption of a resistor is equal to the square of the current (I^2) times the resistance (R).

P = I^2 x R

The complete formula is as follows::

## Resistor Types

Because symbol of resistor are very widely used in electronic devices, there are several types of resistor distribution, including resistors based on resistance value, shape, raw material and use. Therefore it is important that we know these types of resistors.

### 1. Based on Value

When talking about resistance values, resistors are divided into two types, Fixed Resistors and Variable Resistors..

#### a. Fixed Resistor

Fixed resistors are resistors that have a fixed value of resistance. Usually this resistance value can be known based on the color of the bracelet or the number written on the resistor body.

In addition to having a fixed value, this resistor also has a tolerance value, temperature coefficient and power capability.

For self-tolerance, these fixed value resistors have a range from 0.001% to 20%. The smaller the tolerance value, the more accurate the resistance value.

For the temperature coefficient value, this fixed resistor starts from the value range of -1500/ -900ppm/degree Celsius to 1800ppm/degree Celsius.

For power capabilities, these resistors have power capabilities ranging from 0.05W (1/2W) to 150W.

Fixed Resistors are very many derivatives or types depending on the material that makes up the resistor itself, but in general, based on the material of manufacture, it is currently divided into four major groups, namely:

• Carbon Resistor (resistor made with carbon material)
• Film Resistors (resistors made of metal oxide are usually low-power)
• Wire-wound resistors (resistors made with wire windings are usually high power)
• Semiconductor Resistors (resistors made with semiconductor materials)

#### b. Variabel Resistor

A variable resistor is a resistor whose value can be changed. The process of changing this value can occur due to human influence, temperature and light.
These resistors are of several types:
• Potensiometer
• Rheostat
• Thermistor
• Magneto Resistor
• Photoresistor
• Humistor
• Force Sensitive Resistor

### 2. By Shape

Resistors when viewed from a physical form consist of 3 types, namely::
• THT
• SMD
• MELF

### 3. Based on Raw Material

Resistors have many types that can be made based on the composition of the material. Each resistor material has its own advantages and disadvantages.

As for based on the material, the various resistors are::

• Carbon Resistor
• Metal Element Resistors
• Metal Film Resistor
• Thick Film Resistors
• Thin Film Resistors
• Wire Wound Resistors
• Semiconductor Resistor

### 4. Based on Usage

Because the use of this resistor is very wide, it would be nice if we know the type of resistor based on its application, including:

• Power Resistor
• Current Sense
• Resistor Automotive
• Resistor Safety Resistive
• Moisture Resistant Resistor

## How to Calculate Resistor Value

There are two ways to find out the resistance value of a resistor. The first is based on the color band and the second value is listed directly on the body of the resistor. The most basic thing to know the resistor color value is to remember the resistor value table

### 1. Based on Resistor Color Table

In Figure above is a resistor color code chart from 4 bands to 6 bands of color. In addition to determining the resistance value, the color code of the resistor in the 6th ring of the color band is also used to determine the Temperature Coefficient of Resistance (TCR) of a resistance. The unit of this TCR is ppm/°C. (parts per million per degree Cetrigrade).

#### a. How to Read the Bracelet Color Code Resistor Value

You have to remember the resistor value table code above. The priority to remember is the Color and Number column because it already represents the multiplication column.
Take a look at the multiplication column, we can replace the multiplication term with "Number of Zeros".
Look at the brown color, the value is 1. Chocolate is worth 1, meaning that in the bracelet/column the zero multiplier is one.
Red has a value of 2, zero is two and so on and this only applies in the multiplier column.
If you are still confused, here I will give two examples of how we can read the color band on a resistor to find out what the resistance value of the resistor is.

#### b. First Example

Here in Figure 1 there is a resistor that I provide. This resistor has 4 colored bands on the body of the resistor.

Please review the color chart to see the value of the bracelet color. How to calculate resistor color is:

Brown, Black, Orange and Gold
1 ,        0   x  1.000    and  ±5%.
Result is: 10.000 Ohm ±5%
(How to read : 10.000 atau 10K Ohm with ±5%);

#### c. Second Example

How to read the second example resistor is:

Orange, Orange, Red and Gold.
3,        3   x  100    and  ±5%.
Results is : 3.300 Ohm ±5%
(How to read  : 3.300 or 3K3 Ohm with ±5%);

In the two examples above are resistors with 4 color bands, but on the market there are resistors that have 5 to 6 colored bands. Well, to be clearer how to read it, you can look at the following picture

Here are some examples of how to calculate resistor color codes:

The 1 Ohm Resistor Color Code is brown black gold
The 100 Ohm Resistor Color Code is brown black brown
The 1K Ohm Resistor Color Code is Brown Black Red
The 100k Ohm resistor Color Code is Brown Black Yellow.

Black gold black brown resistor is 10 Ohm 5%
Resistor brown black red gold 102 or 1K Ohm 5%
Resistor red red gold gold 2.2 Ohm 5%
Resistor brown black gold gold 1 Ohm 5%

### 2. How to Read SMD Resistor Value

To read the SMD resistor is easier than the resistor that has a color band. Figures 4 and 5 are examples of SMD resistors. Generally SMD resistors have the value listed on the body. Take a look at the following picture:

#### a. First Example

Examples of SMD resistors read 3,300 Ohms or 3K3 Ohms or 3.3K Ohms

#### b. Second Example

Examples of SMD Resistors read 100 Ohm

## Package Shape and Resistor Size

At the beginning of the discovery of resistors, the type of resistor that has two legs is a resistor used in all electronic devices.

However, as technology develops, resistors also evolve. The size of the resistor that is made is getting smaller, so it is designed in such a way that the holder can be attached to the PCB with a small size as well.

Based on the size of the wrapper or body on the resistor, it is currently divided into 3 groups or in English the term "Package".

What is meant by the package here is a group based on the shape and size of the resistor, friends.

There are 3 types of packages that resistors have, namely::
• SMD (Surface Mount Technology)
• Axial
• MELF (Metal Electrode Leadless Face).
SMD resistors are resistors attached to the PCB, with a rectangular and thin shape.

Axial resistors are resistors that have legs or leads.

MELF resistors are resistors in the form of Axial resistors but without legs and include resistors attached to the PCB such as SMD resistors.

For details, please see the following picture.

Gambar 1. Tipe Resistor

SMD and MELF resistors are often used in small dual layer devices. Because of its small size and the soldering position is directly on the PCB without holes, these resistors are used in almost all digital electronic devices such as computers, smartphones, LCD TVs and others.

The size of the SMD resistor is marked with a numeric code such as 0805. The numeric number contains the length and width of a resistor.

For the size of the Axial and MELF resistors, at this time I can't write it down here, because I haven't found a standard size for this resistor. However, from my experience, the size between the legs of the Axial resistor ranges from 0.8 – 1.2 cm with a power of <1 watt. For more details, please see the datasheet of the resistors used.

## Resistor Application

We now understand that a resistor is an electronic component that can block an electric current and have a Symbol of Resistor.

But in electronic circuits, what exactly or when are resistors used in circuits?

This is what we must master in designing and assembling electronic circuits. By knowing the basics of this resistor application, it is hoped that you can easily understand the repair of errors that occur.

There are at least 5 uses of resistors including Current Blockers, Series Resistors, Parallel, Pull-Ups, and Pull-Downs.

### 1. Reduce Current

Well, this is what most people know. Resistors are often used in circuits that require current resistance, such as turning on an LED.

The LED will work if it is supplied with sufficient current. Bright or not an LED depends on how much or a little current is applied to it. However, too much current applied to the LED will cause the LED to be damaged and burn out. Here it is important that we use resistors.

Let's see an example:

Based on the dataseed of an LED, the current that makes the LED glow is 20 mA with a voltage of 2.2V.

In the circuit, the available source voltage is 5V. If the source voltage is given directly to the LED, it is certain that the LED will be damaged because the voltage limit that the LED can accept is 2.2V.

### 2. Series Resistor

#### a. Definition of Series Resistor

A series resistor is a resistor that is connected in series with another resistor. Either two resistors, three resistors and so on.

In addition, resistors can also be connected in parallel and a combination of the two. This is the basics of electronics.

The series resistor circuit is basically like this:

#### b. Series Resistor Function

In electronic circuits, at least the most basic function is to add a certain resistance value and voltage divider.

Why do we have to increase the resistance value?

Resistors have standard values in their production. Resistor manufacturers don't print resistors with that many values.

Take a look at the following pdf, which lists 168 resistor values with a tolerance of 5% commonly produced:

For example in our circuit design, we need a resistor with a value of 12.5K ohms.

However, in the market we get resistors with a value range of 12K ohms, 13K ohms.

How can we make a resistor with a value of 12.5K ohms?

The trick is to add a 12K ohm + 500 ohm resistor = 12.5K ohm.

The Resistor Series Circuit Formula is:

Rtotal = R1 + R2 + R3 + ..... + Rn

R1 = Resistor 1
R2 = Resistor 2
R3 = Resistor 3
Rn = Resistor n

*n = next value

#### Series Resistors As Voltage Dividers

The thing to remember from this series is:

The voltage across each resistor in series is different, while the current for each resistor is the same“.

By their nature, the resistor will create a voltage drop or voltage drop across the series resistor. Notice in the picture below, there are three resistors connected in series.

The applied voltage at points A and B is 10V. Each resistor has a resistance value of 3K, 2K, and 5K Ohms connected in series.

When measuring each voltage on the resistor using a multimeter, the results are 3V, 2V and 5V.

How could this happen?

Explanation:
1. Get The Rtotal

Rtotal = R1 + R2 + R3
= 3K + 2K + 5K = 10K

2. Get Current Flow

I = V/R
= 10V / 10K ohm
= 0.001 A = 1mA

This means that the current through R1, R2 and R3 is 1 mA. The Current remains the same in the series resistor circuit.

Itotal = IR1 = IR2 = IR3

3. Get Voltage in R1

VR1 =  I * R1 = 1mA * 3K
= 3V

4. Get Voltage in R2

VR2 = I * R2
= 1mA * 2K
= 2V

5. Get Voltage in  R3

VR2 = I * R2
= 1mA * 5K
= 5V

#### Example of a Series Resistor

Here is an example and solution to a resistor voltage divider problem with two resistors in series. This formula is the basic formula of Ohm's law.

1. First example

If Vs, R1 and R2 are known, how to find Vout1 and Vout2?

First find the current I first because the current in the series resistor is the same. The formula is I = Vsource / (R1 + R2)

Second look for Vout1. The formula is Vout1 = I.R1
Third, look for Vout2. The formula is Vout2 = I.R2

2. Seconds example

If Vs, Vout1 and Vout2 are known, how to find R1 and R2?

Jawab:

Since R1 and R2 are unknown, the only way is to determine their total. For example, let's say Rtotal is 2K Ohms.

First find the current I first. I = Vsource / 2K
Second find the resistance R1 the formula is R1 = (Vsource - Vout1) / I
Third find the resistance R2 the formula is R2 = (Vsource - Vout2) / I

### 3. Parallel Resistor

#### a. Definition of Parallel Resistor

Parallel Resistors are resistors that are connected in parallel to another resistor. Either two resistors, three resistors and so on. The basic circuit of parallel resistors is as follows:

#### b. Parallel Resistor Function

The function of the Parallel Resistor is to reduce a certain resistance value and to divide the current. The explanation is as follows:

#### Reducing Certain Resistance Value

Why should we reduce the resistance value? Resistors have standard values in their production. Resistor manufacturers don't print resistors with that many values. Take a look at the following pdf, which lists 168 resistor values with a tolerance of 5% commonly produced:

For example in our circuit design, we need a resistor with a value of 2819 ohms or the equivalent of 2.8K Ohms. However, on the market only 2.7K and 3K Ohm resistance resistors can be found.

Then, how can we make a resistor with a value of 2.8K ohms? The trick is to make a parallel resistor using a 3.6K ohm resistor and 13K ohm = 2.8K ohm.

The Resistor Series Circuit Formula is:

Rtotal = 1/R1 + 1/R2 + 1/R3 + ..... + 1/Rn

#### Parallel Resistors As Current Dividers

The voltage across each resistor in parallel is the same, while the current for each resistor is different“.

Notice in the picture below, there are three resistors connected in parallel.

The applied voltage at points A and B is 10V.

Each resistor has a resistance value of 3K, 2K, and 5K Ohms connected in parallel.

How could this happen?

Explanation:
1. Get the Rtotal

Rtotal = 1/R1 + 1/R2 + 1/R3
= 967.74 Ohm

2. Get the current (I1)

I1 =  V / R1
= 10V / 3K
= 0.0033333333333333 A
= 3.3333333333333 mA

3. Get the current (I2)

I2 = V / R2
= 10V / 2K
=  0.005 A
= 5mA

4. Get the current (I3)

I3 = V /  R3
= 10V /  5K
= 0.002 A
= 2mA

5. Get the Itotal

Itotal  = I1 + I2 +  I3
= 3.3mA + 5mA + 2mA
= 10.3333333333333 mA

6. Check again

R = V / I
= 10V / 10.3333333333333 mA
= 10V / 0.0103333333333333 A
= 967.7419 Ohm

### 4. Pull-Up Resistor

Pull-Up circuit is a resistor circuit that is used to make the voltage float or close to the source voltage.

#### a. What are pull-up resistors used for?

If we play with digital electronic circuits, we will be dealing with two conditions 0 or 1.

This Digital Pin accepts digital logic input only, LOW (0) or HIGH (1).

In voltage, logic 0 is 0V and logic 1 is 5V.

However, if we want to know in more detail, actually logic 0 has a range of values, namely:

If Vsource 5V:
• 0 =    0V - 2.5V
• 1 = 2.6V - 5V
If Vsource is 3.3V:
• 0 =    0V - 2.4V
• 1 = 2.5V - 3.3V

The basic circuit of a pull-up resistor is as follows (left)::

#### b. How do pull-up resistors work?

Notice in the picture above (left), when the button is not pressed, the Pin_Digital voltage will be in the 5V position, but when the button is pressed the voltage will change to 0V.

When the button is pressed, the resistor will become a resistance which will keep VCC and GND from short circuiting.

#### c. Examples of Using Pull-Up Resistors

Let's take the example of one of the uses of pull-up resistors is the reset button on the minimum microcontroller system.

On the microcontroller, a button will reset the microcontroller if the reset pin of the microcontroller is given a logic 0 or 0V (remember the voltage range above).

When the button is released (no longer at logic 0), the microcontroller will work by reading program starts from scratch.

#### d. What is the Rated Pull-Up Resistor used?

This is a question that is often asked by new microcontroller users. The value of this pull-up resistor will be different according to the source voltage that drives the microcontroller.
• If Vcc is 5V, can use a 10K Ohm . resistor
• If the Vcc is 3.3V, you can use a 4.7K or 4K7 Ohm resistor

### 5. Resistor Pull-Down

The difference between Pull-Down and Pull-Up resistors is only in their placement.

If Pull-Up, then the resistor is located on the "top" connected to VCC.

If Pull-Down, then the resistor is located on the "bring" connected to Ground.

For how it works is the same. If the button is pressed, then the output voltage is 5V, if not pressed the voltage is 0V.

The value of the Pull-Down resistor is the same as the Pull-Up.

Source: Electronics Fundamentals Book, FLOYD