To be able to read schematics you must know the schematic symbols. But you don’t need to memorize them all. To start with, it’s usually enough to know the battery, resistor, capacitor, transistor, diode, LED, and switch.
Later when you come across symbols you don’t know, you can come back here to identify what it is.
Below is an overview of the most used symbols in circuit diagrams.
The symbol for a battery is shown below.
A large and a small line is suppose to represent one battery cell so that the image below would suggest a two-cell battery of 3 V. But usually people just draw the battery symbol with one or two cells no matter what voltage it is.
Capacitors are either polarized or not. The symbols that are commonly used for the two are shown below.
A polarized capacitor is marked with a “+” sign. It is important to distinguish between these two because the polarized capacitor needs to be placed correctly according to the “+” sign.
The schematic symbol of the resistor are drawn in two different ways. The american style resistor is drawn as a zigzag resistor while the european style resistor is drawn as a rectangular resistor.
Even though I’m from Europe, I like to draw the zigzag version. I think it is easier to draw and looks better.
The potentiometer is drawn in several different ways. The symbol is usually drawn as a resistor with an arrow across it or pointing down on it as the one below.
Schematic Symbols of a Transistor
The most common transistor types are the Bipolar Junction Transistor (BJT), Darlington Transistor, and the Field Effect Transistor (FET). The schematic symbols for these types are shown below:
An Integrated Circuit (IC) is usually shown as a rectangular box with pins. Below, an example of the CMOS IC 4017 is shown.
Here are the schematic symbols for the logic gates:
The inductor symbol looks like a coiled wire as this is what an inductor essentially is.
The symbol of the transformer looks like two inductors with something in between them. Thats’s because that’s basically what a transformer is.
A switch can be represented in numerous ways in a circuit diagram. Below is a few examples:
The operational amplifier or “opamp” is represented as a triangle with two inputs and one output. In some cases, the power supply pins are removed, but you still need to connect them for it to work.
In larger circuit diagrams, you usually have a lot of connections to the power supply. To simplify, it’s common to use power symbols for ground and VDD (or VCC) as shown below.
In circuits where you have a dual supply, that is positive, neutral, and negative – you usually have a third power symbol that looks like the VDD symbol, just upside down.
The symbol for a photoresistor – or Light-Dependent Resistor (LDR) – looks like a resistor in a circle with arrows pointing inwards.
The crystal is a component used to create a stable clock frequency, often for microcontrollers. In circuit diagrams it looks like this:
Fuses are often used in higher-voltage circuits. The fuse symbol looks like this: