Schematics

Schematics are our map to designing, building, and troubleshooting circuits. Understanding how to read and follow schematics is an important skill for any electronics engineer.

Drawing a Schematic

When drawing a schematic you typically start from the power source. This can be a generator, a DC power supply, or the AC power supply from your household outlet but in our case it is a 9V Battery. A 9V battery symbol is that of all batteries which are stacked cells, symbolizing the cells in a battery, where the positive anode of the battery is the longer line and the negative cathode is the shorter line. Typically we only mark two stacked cells even if it has more because this is known from the voltage. To know that it is 9-volts, just annotate it as so.

After the power source, we follow convention current flow clockwise through the circuit and add each component we see from positive to negative. In this example, there is a resistor and LED- Both of which are annotated with their value and identifier.

When drawing a circuit, you have two choices:

Draw the circuit where you form a complete loop between the positive and negative terminals of the power source. This is what we think of when we think circuit because it loops like a circle.
Draw the circuit using positive and negative nodes. This method is used when circuits become very complicated and it is easier to represent using nodes instead of having to wrap back to the positive of negative terminals of the power source.

Reading Schematics: Junctions and Nodes

Wires can connect two terminals together, or they can connect dozens. When a wire splits into two directions, it creates a junction. We represent junctions on schematics with nodes, little dots placed at the intersection of the wires.

Schematic Symbols

Click on the thumbnail of any schematic to learn more about that electronic component!

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.

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).

LDR stands for Light Dependent Resistor. These are made out of materials that change their resistance depending on how much light is hitting their surface. They are made as LDR Dark and LDR Light- which means that some have low resistance in light and some have high resistance in light.

The PTC symbol is actually the generic symbol for a thermistor, a temperature-dependent resistor. Just like LDR's, their resistance changes from an external source- temperature. They are also made to have different resistance ranges for different temperature ranges.

There are two commonly used capacitor 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.

Bipolar Junction Transistors (BJTs): BJTs are three-terminal devices. There are two types of BJTs – NPNs and PNPs – and each has its own unique symbol. The collector (C) and emitter (E) pins are both in-line with each other, but the emitter should always have an arrow on it.

LED stands for Light Emitting Diode. LEDs can be made in all different sizes and colors. Some are made to be multicolored and can be lit to be any color of the rainbow. Just like normal Diodes, LEDs are polarized.

Basic diodes are usually represented with a triangle pressed up against a line. Diodes are also polarized. 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).

Buttons are a simple electronic component. There are two basic types of buttons: PBNO's and PBNC's. This stands for Push Button Normally Open or Closed. Both types can be momentary or Snap Action.

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. Switches with more than one throw, like the SPDT and SP3T add more landing spots for the the actuator. Switches with multiple poles, usually have multiple, alike switches with a dotted line intersecting the middle actuator.

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 look like a pair of disproportionate, parallel lines- more pairs of lines indicate 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.

On really busy schematics you can assign special symbols to node voltages. Positive voltage nodes are usually indicated by an arrow pointing up, while ground nodes usually involve one to three flat lines or a down-pointing arrow or triangle.

Motors are fundamental to the modern world. Electric motors define the 21st century's motion needs. Motors are made from magnetic inductors and permanent magnets.

Fuses protect the modern electronic world from variables and surcharges of electric current. Fused come with different Power and Current Ratings. If current overloads the rating of a fuse, a thin wire overheats and breaks disrupting current flow and saving the other sensitive electronics of the circuit. They can later be replaced.

Speakers produce the sound in many of the electronic devices that we all use daily. This makes a speaker a fairly common component in electronics.

Piezo Buzzers are made with Piezo Crystals. Piezo Crystals, typically some type of quartz, have unique properties where they create a voltage when deformed and vibrate when they have a voltage applied to them. Sounds are just vibrations moving air so Piezo Buzzers can create tones, sounds, and work as functional speakers.

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.

Lamp is just another word we use for Lightbulb in the electronics world. A lamp is a type of light that uses an inductor coil that heats up until it is glowing hot surrounded by glass and is typically filled with inert gas or a vacuum. Note how the symbol looks exactly like an Inductor but with a circle around it representing the glass.

Relays are electronic switches similar to transistors. Unlike transistors though, they are capable of handling high voltages and currents. They also use a magnetic inductor to physically pull switches together or apart instead of having depletion boundaries like transistors.

Transformers are two inductors that use Faraday's Law of Induction to induce voltage and currents on each other. We use transformers to step up or step down voltage.

Integrated Circuits, or IC's, are the chips we are familiar with when we say "computer chip." These chips are filled with micro to nano-sized electrical components. IC's can perform the same processes a complicated circuit can, but all tightly packed into a neat package.

Logic Gates

For more information on Logic Gates beyond their schematic symbols, please visit our Logic Gates page

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