The most comprehensive introduction to resistors

Resistors are among the most common component of electronics. They are an essential component in nearly every circuit. They play a significant part in our most beloved formula, Ohm’s Law.

Basic Resistor Information

Resistors are electronic parts that are characterized by a constant, unchanging electric resistance. The resistance of the resistor hinders the movement of electrons within the circuit.

Resistors can be described as active components, which means that they consume power only (and aren’t able to produce it). Resistors are typically used in circuits to are used to complement actively-operating components such as op-amps microcontrollers, as well as various other electronic circuits. Most commonly, they are employed to restrict the current flowing through them, divide voltages as well as the pull-up of I/O lines.

Resistor units

Resistance to electrical currents can be measured in the ohms. An ohm symbol is greek capital-omega O. The (somewhat circular) meaning of the word 1O refers to difference between two points, where 1 one volt (1V) of potential energy applied will cause 1 amp (1A) in current.

As far as SI unit values are concerned, bigger or less ohm values are matched by an identifier like kilo- mega-, mega- or giga- to make larger values easier to comprehend. It’s common to see resistors that fall in the megaohm (kO) or megaohm (MO) range (much less often do you find milohm (mO) resistances). For instance an O resistor of 4,700O is comparable to an 4.7kO resistor. Likewise, the 5,600,000O resistance could be described in the form of 5,600kO, or (more often)) 5.6MO.

Schematic symbol

All resistors come with 2 terminals with one connection at both ends of the. When it is modeled using an electrical schematic, the resistor appears in one of the following symbols:

Two typical schematic symbols for resistors. R1 is an American-style 1kO resistor while R2 represents an International-style 47kO resistor.

The resistor’s terminals are the lines that extend from the Squiggle (or rectangular). They are what connect the remainder parts of the circuit.

The circuit symbols of the resistor are usually enhanced with an resistance number and an identifier. The value, expressed in ohms, is important for in assessing and actually building the circuit. Its name will usually be composed of an R followed by an ohm. Every resistor in an circuit must be identified by a specific name or number. As an example, here’s several resistors operating on the 555 timer circuit

In this circuit the resistors play an important part in determining how much frequency is generated by the timer’s output. The third resistance (R3) reduces the amount of current flowing that an LED can carry.

Types of Resistors

Resistors are available in a variety of sizes and shapes. They could be through-hole or surface-mount. They could be a conventional static or static resistor, a collection of resistors or a custom variable resistor.

Termination and Mounting

Resistors can be found with two different termination types that are through-hole or surface-mount. These kinds of resistors are generally referred to as PTH (plated through-hole) or SMD/SMT (surface-mount technology or device).

Through-hole resistors are made with long, flexible leads that can be inserted to the shape of a breadboard or soldered by hand onto prototyping boards as well as a printed circuit boards (PCB). They are typically better suited for prototyping, breadboarding or in any situation where you’d prefer not to connect tiny, 0.6mm-long SMD resistors. Long leads typically require trimming. These resistors will take up larger space than surface mount counterparts.

The most commonly used through-hole resistors are found in an axial box. The dimension of an axial resistance is proportional the power it is rated. A typical 1/2 W resistor measures around 9.2mm across, whereas the smaller 1/4 W resistor measures around 6.3mm long.

Half-watt ( 1/2 W) resistor (above) that is sized to the size of a quarter-watt ( 1/4 W).

Surface-mount resistors are typically tiny black rectangles that are connected on either side by smaller, more shiny silver-colored and conductive edges. These resistors are made to be placed in the tops of PCBs which are then soldered to the landing pad that they’re paired with. Because they’re so small, they’re generally put in place by robots robot and then sent through an oven in which solder melts, and then holds them in their place.

A tiny 0603 330O resistor hovering over shiny George Washington’s nose on top of a [U.S. quarter](

SMD resistors are offered in standard sizes, usually 0805 (0.08″ long by 0.05″ wide) 0603 or 0402. They’re great for mass circuit-board-production, or in designs where space is a precious commodity. They require a steady and precise hand to solder manually, but!

Resistor Composition

Resistors are made of various materials. The most popular, modern-day resistors are made of either the carbonor metal or a metal-oxide-based film. In these types of resistors, a thin layer of conductor (though nevertheless resistant) materials is wrapped around and then covered with an insulate material. The majority of standard through-hole resistors that are simple and no-frills are available in carbon-film or a metal-film.

Take a peek inside several carbon-film resistors. The values of resistance from the top to the bottom include 27O, 330O and 3.3MO. In of the resistor, a layer of carbon wraps around the insulation. The more wraps, the higher resistance. It’s pretty cool!

Other through-hole resistors could be wirewound, or made from thin metallic foil. These are typically more costly, premium components that are specifically selected because of their distinctive characteristics, such as an increased power-rating or the maximum temperature range.

Surface-mount resistors are typically either thin or thick-film varieties. Thicker-film tends to be more expensive however it is less exact than thinner. In both types of resistors, small-sized films of metal alloy that resists can be sandwiched in between a base of ceramic and a glass/epoxy layer, it is then joined to the edges of the conductive.

Special Resistor Packaging

There are many different, specially-purpose resistors available there. Resistors are often pre-wired five- or so ranges of resistors. Resistors within these arrays could be connected to a common pin or even be configured to function as voltage dividers.

A set of five resistors 330O that are all connected at the same point.

Variable Resistors (i.e. Potentiometers)

Resistors aren’t required to be static. Variable resistors, also known in the field of rheostats are those that can be set to certain values. The rheostat has a similarity to that of the potentiometer. Pots connect two resistors in the internal circuit in series and then adjust their center tap to create the ability to adjust the voltage divisor. The variable resistors are typically utilized for inputs such as volume knobs, that need to be able to adjust.

A variety of potentiometers. From the top left, clockwise: the standard 10k trimpot 2-axis joystick, softpot slide pot, the classic right-angle and a breadboard-friendly 10k trimpot.

Decoding Resistor Markings

While they don’t display their worth in a clear manner, the majority of resistors are marked to indicate how much resistance they have. PTH resistors utilize the color-coding system (which is a great way to add some interest to circuits) as do SMD resistors are equipped with their own system of value marking.

Understanding the Color Bands

Through-hole, axial resistances generally utilize the color-band system for displaying their worth. The majority of these resistors feature four color bands around the resistor, however you can also find six and five band resistors.

Four Band Resistors

In the typical four-band resistors, the first two bands represent the two most significant numbers of the value of the resistor. The third band represents an amount of weight that is multiplied by the two digits that are significant by a power of 10.

The last band is how much the tolerance for the resistor. The tolerance is the amount of less or more is the actually resistance to the resistor is in comparison to the nominal value. The resistor cannot be manufactured to be perfect, and various manufacturing techniques can result in higher or lower tolerances. For instance, a resistor that has 5 percent tolerance can vary from 0.95kO or 1.05kO.

What is the best way to determine which band is the one that is first and which is the last? The lastband, known as the tolerance band is usually clearly distinguished by the values bands and typically, it’s silver or gold.

Resistors in the Five and Six Bands

Five band resistors feature an additional important digit band in between the two bands that precede it and also the multiplyer band. They also have more tolerance options offered.

Six-band resistors are five band resistors that have an additional band on the other end which is that the coefficient of temperature. This is the anticipated changes in the resistor’s value depending on the temperature change in degrees Celsius. The temperature coefficients are quite small, even in the ppm-ppm range.

Decoding Color Bands of Resistor

To decode the color codes of resistor bands, refer to a table of color codes for resistors similar to the one shown below. For the two bands that are first you need to find the color’s numeral value. The 4.7kO resistor displayed here contains two color bands – violet and yellow with digits between 4 and (47). The third color band of 4.7kO color is red. This suggests that the 47 must be multiplied 10 two (or 100). 47 times 100 is 4,700! 4.7kO resistor that has four bands of color

If you’re looking to commit the color code to memory using a mnemonic device, it could assist. There are a few (sometimes not-so-savory) Mnemonics available to help you remember the color code for the resistor. A great one that explains the difference between lack and brown, is:lack and rown is:rown is:

“Big brown rabbits usually give huge vocal groans when snapped with care.”

If you are able to have a memory of “ROY G. BIV” then subtract that of the indigo (poor indigo as no one can remember indigo) and add brown and black to the front, and white and gray in the rear of the traditional rainbow color order.

The Resistor Color Code Table

Have difficulties seeing? Click the image to get a greater clarity!

Resistor Color Code Calculator

If you’d prefer to skip the math (we don’t care! ) instead, you can utilize a calculator that is easy to use try an one of these calculators a shot!

Four Band Resistors

Band 1   Band 2   Band 3                   Band 4

  1. (MSV) Value 2 Weight                  Tolerance

Resistance: 1kO + -5 1 %

Resistors in the Five and Six Band

Note: Calculate your six-band resistor here. Be certain to add an appropriate temperature coefficient onto the value you want to get for the resistor

Band 1   Band 2   Band 3   Band 4                   Band 5

  1. (MSV) Value 2 3              Weight                  Tolerance

Resistance: 1kO + -5 1 %

Understanding Surface-Mount Markings

SMD resistors, such as the ones in 0603 and 0805 packages, come with different ways to display their worth. There are several commonly used marking methods that you’ll encounter in these resistances. They’ll typically feature three to four characters, either numbers or letters over the top on the front of the box.

When the 3 characters that you’re looking at appear to be each a number it’s likely that you’re seeing the E24 mark resistor. These marks actually have some similarities with the color-band systems used on PTH resistors. Two numbers are the primary two most significant digits of the value, and the last number indicates the magnitude.

In the image above in the above example, resistors are labeled in the following order: 104,105, 205 751, 751, and 754. The resistor with the number 104 is 100kO (10×104) 751 is 1MO (10×105) and 205 will be two MO (20×105). 751 is 751O (75×10 1) 754 is 750O (75×10 1), and 754 is 754kO (75×10 4).

Another popular system of coding one of the most popular is E96 and is one of the more obscure of all. The resistors in E96 will be identified with three characters: 2 numbers in the start and an ending letter. Two numbers reveal the initial three numbers of the value, matching with one of the less obvious values in this table.

Code       Value                      Code       Value                      Code       Value                      Code       Value                      Code       Value                      Code       Value

01           100                         17           147                         33           215                         49           316                         65           464                         81           681

02           102                         18           150                         34           221                         50           324                         66           475                         82           698

03           105                         19           154                         35           226                         51           332                         67           487                         83           715

04           107                         20           158                         36           232                         52           340                         68           499                         84           732

05           110                         21           162                         37           237                         53           348                         69           511                         85           750

06           113                         22           165                         38           243                         54           357                         70           523                         86           768

07           115                         23           169                         39           249                         55           365                         71           536                         87           787

08           118                         24           174                         40           255                         56           374                         72           549                         88           806

09           121                         25           178                         41           261                         57           383                         73           562                         89           825

10           124                         26           182                         42           267                         58           392                         74           576                         90           845

11           127                         27           187                         43           274                         59           402                         75           590                         91           866

12           130                         28           191                         44           280                         60           412                         76           604                         92           887

13           133                         29           196                         45           287                         61           422                         77           619                         93           909

14           137                         30           200                         46           294                         62           432                         78           634                         94           931

15           140                         31           205                         47           301                         63           442                         79           649                         95           953

16           143                         32           210                         48           309                         64           453                         80           665                         96           976


The last letter signifies a multiplier, a match to the following table:

Letter     Multiplier                              Letter     Multiplier                              Letter     Multiplier

Z              0.001                     A             1                              D             1000

If R or Y, 0.01                        B or H    10                           E              10000

X or S     0.1                          C              100                         F              100000




Therefore, an 01C resistor is our great friend 10,010O (100×100), 01B is 1kO (100×10) Then 01D is 100kO. They are straightforward, however, other codes might not be. 85A from the above image can be interpreted as the 750O (750×1) as well as 30C is actually 20kO.

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