What are resistors? – Understanding Circuit Building Components

As you dive deeper into electronics, it is important to become familiar with the essential components found in many circuits.

Resistors are one of the building blocks engineers get to know like the back of their hand. Learning about resistors will help you grow your skills and tackle bigger, more exciting projects.

What does a resistor do?

A resistor is a circuit component that does exactly what its name suggests: Resists. Adding a resistor to a circuit reduces the amount of electric current that can pass through the circuit.

Nearly every circuit you encounter uses a resistor in some way. For example, LED circuits, like the ones in our Blink and Hue kits, use current-limiting resistors to protect the components from being overpowered by current and burning out! Resistors are also used to control the brightness of the LEDs.

Beyond the basic limiting of current, resistors can be used in more complex and clever applications. Some electronic components require a specific amount of voltage. Adding resistors to a circuit can reduce the voltage used by these other components. 

Understanding how a resistor will impact the circuit as a whole is explained by a nifty scientific law called Ohm’s Law.

Resistors are also commonly combined with capacitors, which store energy. These are often referred to as RC circuits and can work in tandem to control frequency filters, current supply, and various other applications.

What does it look like on a schematic?

Resistors are represented by “squiggly” lines or by empty rectangles depending on the type of diagram you are reading.

Next to the resistor symbol on the schematic, there will be either a number or a variable. If it is a variable, it will correspond to a number somewhere else in the documentation. That number indicates the resistance in Ohms (Ω) for that resistor.

What do the colors mean on a resistor?

Resistors use a clever color code to indicate their resistance value in Ohms (Ω).

To read the resistor value, you need to first identify what side is which. Commonly, one side will have a metallic gold or silver band (indicating the tolerance of the resistor value). Resistors are typically read from left to right with this tolerance band on the right side (see chart below).

If you don't see a metallic band (or can't tell), there should also be a slightly larger gap between the tolerance band and the band next to it compared to the other side.

The most common type of resistor you'll likely come across in prototyping circuits is the 4-band style (usually tan) but you might run also across 5 or even 6-band resistors. The first two stripes always indicate the first two digits in the Ohm(Ω) resistance value.

A third stripe is used as a multiplier - how many zeros follow the value. And, a fourth stripe is used for tolerance. On rare occasions, you might see a 6-band resistor with an extra band at the end to indicate a Temperature Coefficient. 

By following this system, you can calculate resistor values easily and clearly. A yellow, purple, orange, and gold pattern indicates a 47,000 Ω resistor ± 5%.

This handy chart is included on our Heat Resistant Silicone Mat if you'd like it as a fun colorful reference while soldering and building circuits.

When in doubt, you can always test resistance with a multimeter or punch in the colors you see to an online resistor calculator.

Do resistors have polarity? Does the direction of a resistor matter?

No! Unlike many other components, resistors do not have polarity, meaning you can install them in either direction on a circuit. Also, it does not matter if you are using a through-hole part or surface mount part–the principles and functions of resistors are the same!

How do I add a resistor to a circuit?

Adding a resistor to your circuit comes down to reading a circuit board correctly and soldering in the correct place.

In the Blink and Hue Learn to Solder Kits, the online instructions provide detailed information about installing the resistors so that anyone without prior experience can understand how to do it. Plus, you get great experience learning how to solder resistor components!