Maria Montero

Electrical Symbols for Electronic Components – Passive Components

Learn the electrical symbols for basic electronic components, including passive components (resistors, capacitors, inductors, transformers), diodes, and thyristors.

Electrical symbols are a short way to indicate which components are involved in a circuit diagram. They provide a quick guide to a design for visual communication, an essential aspect of engineering. I can’t imagine a design review meeting that doesn’t involve a carefully drawn outline. Despite the proliferation of projectors and digital tablets and other things, I suspect that many engineers have not found a suitable substitute for physical schematic prints that can be closely examined and marked with a pencil.

Even if no one else is going to see your design, a good schematic can help you organize your thoughts, reflect on the functionality of a circuit, and find errors when they are very easy to correct (i.e. prior to The board has been sent to the fabulous house.

There is no doubt that some of this information is a bit elementary. However, if you read both articles to the end, I think you will find several details that will be new information for some readers and good reminders for many others.

Note: This guide will focus on North American symbols. If there is enough interest from the community, we will supplement it with symbols popular in other parts of the world.

Related information

Symbols for resistors

The general idea of ​​a resistance symbol presents no difficulties, but putting this theory into practice is surprisingly difficult. How many peaks and valleys should there be? Does the first diagonal line go up or down? Should the number of peaks equal the number of valleys? What is the ideal slope of the diagonal lines? There is currently no agreed answer to all of these questions in the industry.

Of course, all these questions would be definitely solved if everyone just adopted me Symbol of resistance (which is undoubtedly the best in the world):

Electrical symbol for resistors.

Now we will move on to some components that are extensions of the basic resistor. First, there are resistors that have a non-fixed resistance, rheostats, and potentiometers.


If a device is simply a variable resistor, it is called rheostat. This is a two terminal device that allows the user to mechanically adjust the resistance between the terminals.

Rheostatic symbol


A three-terminal variable resistor is a potentiometer. The third terminal (called the wiper) allows the device to function as a variable voltage divider, although a potentiometer can be used as a rheostat by connecting the external circuit to the windshield wiper and one of the other two terminals.

Potentiometer symbol


Mechanical movement is not the only thing that can change the resistance of a component. A variable resistor that is controlled by light is called photoresistor or a LDR (light dependent resistor). As you might expect, these devices are useful when the behavior of a circuit must be influenced by the intensity of light; Take a look at this article to learn more.

Photoresist symbol, also known as LDR


If the resistance of a variable resistor is governed by temperature, we have a thermistor.