SCHEMATIC SYMBOL
Electronic component symbols are used to denote the components in circuit diagrams. There are standard symbols for each of the components which represent that particular component.
RESISTORS
The most fundamental of circuit components and symbols! Resistors on a schematic are usually represented by a few zig-zag lines, with two terminals extending outward. Schematics using international symbols may instead use a featureless rectangle, instead of the squiggles.
POTENTIOMETER AND VARIABLE RESISTOR
Variable resistors and potentiometers each augment the standard resistor symbol with an arrow. The variable resistor remains a two-terminal device, so the arrow is just laid diagonally across the middle. A potentiometer is a three-terminal device, so the arrow becomes the third terminal (the wiper).
CAPACITORS
There are two commonly used capacitors symbols. One symbol represents a polarized (usually electrolytic or tantalum) capacitor, and the other is for non-polarized caps. In each case there are two terminals, running perpendicularly into plates.
The symbol with one curved plate indicates that the capacitor is polarized. The curved plate usually represents the cathode of the capacitor, which should be at a lower voltage than the positive, anode pin. A plus sign should also be added to the positive pin of the polarized capacitor symbol.
INDUCTORS
Inductors are usually represented by either a series of curved bumps, or loopy coils. International symbols may just define an inductor as a filled-in rectangle.
SWITCHES
Switches exist in many different forms. The most basic switch, a single-pole/single-throw (SPST), is two terminals with a half-connected line representing the actuator (the part that connects the terminals together).
POWER SOURCES
Just as there are many options out there for powering your project there are a wide variety of power source circuit symbols to help specify the power source.
DC or AC Voltage Sources
Most of the time when working with electronics, you’ll be using constant voltage sources. We can use either of these two symbols to define whether the source is supplying direct current (DC) or alternating current (AC):
BATTERIES
Batteries, whether they’re those cylindrical, Alkaline AA ‘s or rechargeable lithium polymer, usually look like a pair of disproportionate, parallel lines:
More pairs of lines usually indicates more series cells in the battery. Also, the longer line is usually used to represent the positive terminal, while the shorter line connects to the negative terminal.
VOLTAGE NODES
Sometimes — on really busy schematics especially — you can assign special symbols to node voltages. You can connect devices to these one-terminal symbols, and it’ll be tied directly to 5V, 3.3V, VCC, or GND (ground). Positive voltage nodes are usually indicated by an arrow pointing up, while ground nodes usually involve one to three flat lines (or sometimes a down-pointing arrow or triangle).
DIODES
Basic diodes are usually represented with a triangle pressed up against a line. Diodes are also polarized, so each of the two terminals require distinguishing identifiers. The positive, anode is the terminal running into the flat edge of the triangle. The negative, cathode extends out of the line in the symbol (think of it as a – sign).
There are a all sorts of different types of diode, each of which has a special riff on the standard diode symbol. Light-emitting diodes (LEDs) augment the diode symbol with a couple lines pointing away. Photodiodes, which generate energy from light (basically, tiny solar cells), flip the arrows around and point them toward the diode.
TRANSISTORS
Transistors, whether they’re BJTs or MOSFETs, can exist in two configurations: positively doped, or negatively doped. So for each of these types of transistor, there are at least two ways to draw it.
Bipolar Junction Transistors (BJTs)
BJTs are three-terminal devices; they have a collector (C), emitter (E), and a base (B). There are two types of BJTs — NPNs and PNPs — and each has its own unique symbol.
FUSES
Fuses and PTCs — devices which are generally used to limit large inrushes of current — each have their own unique symbol:
