Reading Schematics

Reading schematics can be difficult for beginners since there are many symbols. This guide is intended to help people with any background in electronics (including none) become able to read and understand an electronic circuit schematic diagram. My advice is to start out with small simple schematics, eventually progressing to more complicated schematics as you become more comfortable with the symbology.

To read a schematic, you require no understanding of how a circuit actually works, although it might help with troubleshooting. However, you must be able to realize what component each symbol represents and how to connect them.

In a schematic, all components should be clearly labeled with a part number or size. For resistors, the size in Ohms should be labeled, while capacitors should have the size in Farads labeled. If a component is not marked, it may have been missed by the drawer of the schematic or it may not matter what size resistor is put in place.

Wires in schematics are represented by lines. Connections between wires are represented by dots on the point where the lines intersect. If two wires cross, but one has a curve over the intersection, it means that the two wires aren't connected and only cross to make drawing the schematic easier.

Switches are usually classified into two types: momentary and toggle switches. A toggle switch is a line with part of it removed and pointing outwards. A momentary switch is two broken lines with a third parallel line to the side of it, representing a push button.

Battery cells are represented by two parallel lines, with one shorter than the other. In some schematics you will see only one battery cell, while others will put more than one in a row. The number of cells is usually arbitrary since the voltage is clearly marked. It should also be noted that the longer line represents the positive terminal of the battery.

Resistors are either represented by 3-4 triangular waves or a rectangular block. A potentiometer or variable resistor is the same, only with an arrow pointing perpendicular to the standard resistor.

Unpolarized capacitors are represented by two lines of equal length perpendicular to the wires that enter them. Polarized capacitors are either the same as an unpolarized capacitor with a positive polarity indicator or one of the lines may be replaced by a curved line, which represents the negative polarity.

Inductors are represented by numerous semicircles in a row, representing turns of wire. If there are two lines to the side of the inductor, it indicates that it is wrapped around a ferrous material, such as an iron bar. Transformers are two or more inductors next to the same parallel lines. With transformers, the number of loops can either be labeled or represented by the number of "loops" in each inductor component.

Transistors are represented by a line perpendicular to the wire, with two additional lines coming out of the opposing side of the line. Often, one of the lines has an arrow to indicate that it is the collector or emmiter. In many cases, the transistor is also encircled.

Diodes are represented by a line perpendicular to the wire with a small arrow indicating the polarity. Light emitting diodes (LEDs) are the same as diodes, only with two or more arrows coming off, indicating light. LED symbols are often encircled to further differentiate them from standard diodes.

DC voltage supplies are represented by circles with positive and negative markings to indicate polarity. DC current sources are represented by circles with an arrow representing the direction of current flow. AC power supplies are represented by a circle containing a sine, square, or sawtooth wave.

Earth grounds are represented by a series of three lines perpendicular to the wire with decreasing size.

An integrated circuit is usually represented by a triangle with markings indicating which wires connect to which pins. In some cases, the entire integrated circuit will be drawn in as a rectangle with pins labeled.

Chart of Schematic Symbols

Toggle Switch Symbol
Momentary Switch Symbol
Battery Symbol
Resistor Symbol
Variable Resistor Symbol
Polarized Capacitor
Inductor Symbol
Transformer Symbol
Transistor Symbol
Diode Symbol
Sine Wave AC Power Supply Symbol
Earth Ground Symbol
Integrated Circuit Symbol

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