# data[].attributes.body
A circuit diagram (electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while aschematic diagram shows the components and interconnections of the circuit using standardized symbolic representations. The presentation of the interconnections between circuit components in the schematic diagram does not necessarily correspond to the physical arrangements in the finished device.[1]

Unlike a block diagram or layout diagram, a circuit diagram shows the actual electrical connections. A 21drawing meant to depict the physical arrangement of the wires and the components they connect is called artwork or layout, physical design, or wiring diagram.

Circuit diagrams are used for the design (circuit design), construction (such as PCB layout), and maintenance of electrical and electronic equipment.

In computer science, circuit diagrams are useful when visualizing expressions using Boolean algebra.[2]

Contents

[show]

Symbols[edit]

Main article: Electronic symbol

Circuit diagrams are pictures with symbols that have differed from country to country and have changed over time, but are now to a large extent internationally standardized. Simple components often had symbols intended to represent some feature of the physical construction of the device. For example, the symbol for a resistor shown here dates back to the days when that component was made from a long piece of wire wrapped in such a manner as to not produce inductance, which would have made it a coil. These wirewound resistors are now used only in high-power applications, smaller resistors being cast from carbon composition (a mixture of carbon and filler) or fabricated as an insulating tube or chip coated with a metal film. The internationally standardized symbol for a resistor is therefore now simplified to an oblong, sometimes with the value in ohms written inside, instead of the zig-zag symbol. A less common symbol is simply a series of peaks on one side of the line representing the conductor, rather than back-and-forth as shown here.

Wire Crossover Symbols for Circuit Diagrams. Note that the CAD symbol for insulated crossing wires is exactly the same as the older, non-CAD symbol for non-insulated crossing wires. To avoid confusion, the wire "jump" (semi-circle) symbol for insulated wires in non-CAD schematics is recommended (as opposed to using the CAD-style symbol for no connection), so as to avoid confusion with the original, older style symbol, which means the exact opposite. The newer, recommended style for 4-way wire connections in both CAD and non-CAD schematics is to stagger the joining wires into T-junctions.[3]

The linkages between leads were once simple crossings of lines. With the arrival of computerized drafting, the connection of two intersecting wires was shown by a crossing of wires with a "dot" or "blob" to indicate a connection. At the same time, the crossover was simplified to be the same crossing, but without a "dot". However, there was a danger of confusing the wires that were connected and not connected in this manner, if the dot was drawn too small or accidentally omitted (e.g. the "dot" could disappear after several passes through a copy machine).[4] As such, the modern practice for representing a 4-way wire connection is to draw a straight wire and then to draw the other wires staggered along it with "dots" as connections (see diagram), so as to form two separate T-junctions that brook no confusion and are clearly not a crossover.[5][6]

For crossing wires that are insulated from one another, a small semi-circle symbol is commonly used to show one wire "jumping over" the other wire[3][7][8] (similar to how jumper wires are used).

A common, hybrid style of drawing combines the T-junction crossovers with "dot" connections and the wire "jump" semi-circle symbols for insulated crossings. In this manner, a "dot" that is too small to see or that has accidentally disappeared can still be clearly differentiated from a "jump".[3][7]

On a circuit diagram, the symbols for components are labelled with a descriptor or reference designator matching that on the list of parts. For example, C1 is the first capacitor, L1 is the first inductor, Q1 is the first transistor, and R1 is the first resistor (note that this is not written as a subscript, as in R1, L1,...). Often the value or type designation of the component is given on the diagram beside the part, but detailed specifications would go on the parts list.

Detailed rules for reference designations are provided in the International standard IEC 61346

A circuit diagram (electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while aschematic diagram shows the components and interconnections of the circuit using standardized symbolic representations. The presentation of the interconnections between circuit components in the schematic diagram does not necessarily correspond to the physical arrangements in the finished device.[1]

Unlike a block diagram or layout diagram, a circuit diagram shows the actual electrical connections. A drawing meant to depict the physical arrangement of the wires and the components they connect is calledartwork or layout, physical design, or wiring diagram.

Circuit diagrams are used for the design (circuit design), construction (such as PCB layout), and maintenance of electrical and electronic equipment.

In computer science, circuit diagrams are useful when visualizing expressions using Boolean algebra.[2]

Contents

[show]

Common schematic diagram symbols (US symbols)

The circuit diagram for a four-bit TTLcounter, a type of state machine

It is a usual although not universal convention that schematic drawings are organized on the page from left to right and top to bottom in the same sequence as the flow of the main signal or power path. For example, a schematic for a radio receiver might start with the antenna input at the left of the page and end with the loudspeaker at the right. Positive power supply connections for each stage would be shown towards the top of the page, with grounds, negative supplies, or other return paths towards the bottom. Schematic drawings intended for maintenance may have the principal signal paths highlighted to assist in understanding the signal flow through the circuit. More complex devices have multi-page schematics and must rely on cross-reference symbols to show the flow of signals between the different sheets of the drawing.

Detailed rules for the preparation of circuit diagrams, and other document types used in electrotechnology, are provided in the international standard IEC 61082-1.

Relay logic line diagrams, also called ladder logic diagrams, use another common standardized convention for organizing schematic drawings, with a vertical power supply rail on the left and another on the right, and components strung between them like the rungs of a ladder.

Artwork[edit]

A rat's nest

Once the schematic has been made, it is converted into a layout that can be fabricated onto a printed circuit board (PCB). Schematic-driven layout starts with the process of schematic capture. The result is what is known as a rat's nest. The rat's nest is a jumble of wires (lines) criss-crossing each other to their destination nodes. These wires are routed either manually or by the use of electronics design automation (EDA) tools. The EDA tools arrange and rearrange the placement of components and find paths for tracks to connect various nodes. This results in the final layout artwork for the integrated circuit or printed circuit board.[9]

A generalized design flow may be as follows:

Schematic → schematic capture → netlist → rat's nest → routing → artwork → PCB development and etching → component mounting → testing

Light switch                                                                                               Doorbell

Circuit Science Projects

13

Build a Circuit

A circuit is a path that electricity flows along. It starts at a power source, like a battery, and flows through a wire to a light bulb or other object and back to other side of the power source. You can build your own circuit and see how it works with this project!

What You Need:

Small light bulb (or a flashlight bulb)

2 batteries (with the correct voltage for your light bulb)

2 alligator clip wires or aluminum foil*

Paper clips

Electrical tape (Scotch®tape also works)

Bulb holder (optional)

Battery holders (optional**)

*To use foil instead of wires, cut 2 strips each 6" long and 3" wide. Fold each one tightly along the long edge to make a thin strip.)

**To use paper clips instead of battery holders, tape one end of a paper clip to each end of your battery using thin strips of tape. Then connect your wires to the paper clips.

Part 1 - Making a Circuit:

1. Connect one end of each wire to the screws on the base of the light bulb holder. (If you're using foil, ask an adult to help you unscrew each screw enough to fit a foil strip under it.)

2. Connect the free end of one wire to the negative ("-") end of one battery. Does anything happen?

3. Attach the free end of the other wire to the positive ("+") end of the battery. Now what happens?

Part 2 - Adding Power

1. Disconnect the battery from your circuit. Stand one battery so that the "+" end is pointing up, then set the other battery next to it so that the flat "-" end is pointing up. Tape around the middle of the batteries to hold them together.

2. Set a paperclip across the batteries so that it connects the "+" end of one to the "-" end of the other. Tape the paperclip in place with a narrow piece of tape (do not tape over the metal battery ends).

3. Turn the batteries over and tape one end of a paper clip onto each of the batteries. Now you can connect one wire to each paper clip. (The bottom of the battery pack should only have one paper clip - do not connect a wire to it.)

4. Connect the free ends of the wires to the light bulb.

(Note: Instead of steps 1-3, you can use two batteries in battery holders and connect them together with one wire.)

What Happened:

In the first part, you made a simple circuit that used a battery to light up a light bulb. Batteries supply electricity. When they're connected properly, they can "power" things, like a flashlight, an alarm clock, a radio, or a timer. Why didn't the light bulb light up when you connected it to one end of the battery with a wire? Electricity from a battery has to flow out one end (the negative or "-" end) and back in through the positive ("+") end in order to work. What you built with the battery, wire, and bulb in step 3 is called an open circuit. In order for electricity to start flowing, you need aclosed circuit. Electricity is caused by tiny particles with negative charges, called electrons. When a circuit is complete, or closed, electrons can flow from one end of a battery all the way around, through the wires, to the other end of the battery. Along its way, it will carry electrons to electrical objects that are connected to it - like the light bulb - and make them work!

In the second part, you added another battery. That should have made the light bulb burn more brightly, because two batteries together can supply more electricity than just one! The paper clip across the bottom of the battery pack allowed electricity to flow between the batteries, making the flow of electrons stronger.

Do you see how closed and open circuits work to allow or stop electricity from flowing?

Insulator or Conductor?

Materials that electricity can flow through are call conductors. Materials that stop electricity from flowing are called insulators. You can find out which things around your house are conductors and which are insulators using the circuit you made in the last project to test them!

What You Need:

Circuit with light bulb & 2 batteries

Extra alligator clip wire (or aluminum foil wire*)

Objects to test (made of metal, glass, paper, wood, and plastic)

Worksheet (optional)

What You Do:

1. Disconnect one of the wires from the battery pack. Connect one end of the new wire to the battery. You should have two wires with free ends (between the light bulb and the battery pack).

2. You have made an open circuit and the bulb should not light up. Next you will test objects to see if they are conductors or insulators. If the object is a conductor, the light bulb will light up. It is is an insulator, it will not light. For each object, guess whether you think each object will complete the circuit and light up the light bulb or not.

3. Connect the ends of the free wires to an object and see what happens. Some objects you could test are a paper clip, a pair of scissors (try the blades and the handles separately), a glass, a plastic dish, a wooden block, your favorite toy, or anything else you can think of.

What Happened:

Before you test each object, guess whether it will make the light bulb light up or not. If it does, the object you're touching the wires to is a conductor. The light bulb lights up because the conductor completes, or closes, the circuit and electricity can flow from the battery to the light bulb and back to the battery! If it doesn't light up, the object is an insulator and it stops the flow of electricity, just like an open circuit does.

When you set up the circuit in step 1, it was an open circuit. Electrons could not flow all the way around because two of the wires were not touching. The electrons were interrupted. When you placed an object made of metal between the two wires, the metal closed or completed the circuit - the electrons could flow across the metal object to get from one wire to the next! Objects that completed the circuit made the light bulb light up. Those objects are conductors. They conduct electricity. Most other materials, like plastic, wood, and glass are insulators. An insulator in an open circuit does not complete the circuit, because electrons cannot flow through it! The light bulb did not light up when you put an insulator in between the wires.

If you're using wires or alligator clips, take a good look at them. Inside they are made of metal, but they have plastic around the outside. Metal is a good conductor. Plastic is a good insulator. The plastic wrapped around the wire helps keep electrons flowing along the metal wire by blocking them from transferring to other object outside of the wires

Circuit Diagram

A circuit diagram is a visual display of an electrical circuit using either basic images of parts or industry standard symbols. Symbol usage depends on the audience viewing the diagram. These two different types of circuit diagrams are called pictorial (using basic images) or schematic style (using industry standard symbols). A schematic style circuit diagram is used to give a visual representation of an electrical circuit to an electrician. The pictorial style circuit diagram would be used for a broader, less technical audience.

Symbols Used in Circuit Diagrams

There are hundreds of different symbols that can be used in a circuit diagram. These include simple images of objects such as a battery or a resistor for a pictorial style circuit diagram, or industry-standard symbols for objects such as capacitors or inductors.

In conjunction with circuit diagram symbols, there are also a series of different types of line styles to connect objects. In the event lines cross, use line hops to show wire crossover. It is important to understand who will be viewing the circuit diagram to ensure use of the correct types of symbols.

How to Create a Circuit Diagram

There are many different ways to create a circuit diagram. They can be created manually, but the more efficient way is to use diagramming software such as SmartDraw, which is designed for this purpose. Diagramming software that is specifically designed for creating a circuit diagram offers several advantages.

It is fast and allows for simple construction.

It provides access to thousands of symbols.

It is easy to share electronically.

It provides precise placement of objects.

It is easy to edit.

SmartDraw allows you to quickly, accurately, and easily create a circuit diagram. It also allows you to create personal custom libraries of symbols you commonly use.

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow

Overview

Welcome to circuits 101! One of the first things you’ll encounter when learning about electronics is the concept of a circuit. This tutorial will explain what a circuit is, as well as discuss voltage in further detail.

A simple circuit, involving a button, an LED, and a resistor, built two different ways.

Suggested Reading

There are a few concepts you should have a good understanding of to help you get the most out of this tutorial.

What is Electricity?

Electric Power

Voltage, Current, Resistance, and Ohm’s Law

Alternating Current (AC) vs Direct Current (DC)

Polarity

Circuit Basics

Voltage and How it Works

You’ve probably heard that a battery or a wall outlet has a certain number of volts. This is a measurement of the electrical potential produced by the battery, or the utility grid connected to the wall outlet.

All those volts are sitting there waiting for you to use them, but there’s a catch: in order for electricity to do any work, it needs to be able to move. It’s kind of like a blown-up balloon; if you pinch it off, there is air in there thatcould do something if it’s released, but it won’t actually do anything until you let it out.

Unlike air coming out of a balloon, electricity can only flow through materials that can conduct electricity, such as copper wire. If you connect a wire to a battery or wall outlet (WARNING: the voltage in a wall outlet is dangerous, don’t do this!), you will be giving the electricity a path to follow. But if the wire isn’t connected to anything else, the electricity won’t have anywhere to go and still won’t move.

What makes electricity move? Electricity wants to flow from a higher voltage to a lower voltage. This is exactly like the balloon: the pressurized air in the balloon wants to flow from inside the balloon (higher pressure) to outside the balloon (lower pressure). If you create a conductive path between a higher voltage and a lower voltage, electricity will flow along that path. And if you insert something useful into that path like an LED, the flowing electricity will do some work for you, like lighting up that LED. Huzzah!

So, where do you find a higher voltage and a lower voltage? Here’s something really useful to know: every source of electricity has two sides. You can see this on batteries, which have metal caps on both ends, or your wall outlet that has two (or more) holes. In batteries and other DC (Direct Current) voltage sources, these sides (often calledterminals) are named positive (or “+”), and negative (or “-”).

Why does every source of electricity have two sides? This goes back to the idea of “potential”, and that you need a voltage difference in order to get electricity to flow. It sounds silly, but you can’t have a difference without two things to be different. In any power supply, the positive side will have a higher voltage than the negative side, which is exactly what we want. In fact, when we measure voltage, we usually say that the negative side is 0 volts, and the positive side is however many volts the supply can provide.

Electrical sources are like pumps. Pumps always have two sides, an outlet that blows something out, and an inlet that sucks something in. Batteries and generators and solar panels work the same way. Something inside them is hard at work moving electricity towards the outlet (the positive side), but all that electricity leaving the device creates a void, which means that the negative side needs to pull electricity in to replace it.*

What have we learned so far?

Voltage is potential, but electricity needs to flow to do anything useful.

Electricity needs a path to flow through, which must be an electrical conductor such as copper wire.

Electricity will flow from a higher voltage to a lower voltage.

DC voltage sources always have two sides, called positive and negative, with the positive side a higher voltage than the negative side.

The Simplest Circuit

We’re finally ready to make electricity work for us! If we connect the positive side of a voltage source, through something that does some work such as a Light Emitting Diode (LED), and back to the negative side of the voltage source; electricity, or current, will flow. And we can put things in the path that do useful things when current flows through them, like LEDs that light up.

This circular path, which is always required to get electricity to flow and do something useful, is called a circuit. A circuit is a path that starts and stops at the same place, which is exactly what we’re doing.

Click this link to see a simulation of current flowing through a simple circuit. This simulation requires Java to run.

*Benjamin Franklin originally wrote that electricity flows from the positive side of a voltage source to the negative side. However, Franklin had no way of knowing that electrons actually flow in the opposite direction - at the atomic level, they come out of the negative side and loop back to the positive side. Because engineers followed Franklin’s lead for hundreds of years before the truth was discovered, we still use the “wrong” convention to this day. Practically speaking this detail doesn’t matter, and as long as everyone uses the same convention, we can all build circuits that work just fine.

Short and Open Circuits

What is a “Load”?

The reason we want to build circuits is to make electricity do useful things for us. The way we do that is by putting things in the circuit that use the current flow to light up, make noise, run programs, etc.

These things are called loads, because they “load down” the power supply, just like you’re “loaded down” when you’re carrying something. The same way you could be loaded down with too much weight, it’s possible to load down a power supply too much, which will slow down the current flow. But unlike you, it’s also possible to load down a circuit too little - this may let too much current flow (imagine running too fast if you weren’t carrying any weight), which can burn out your parts or even the power supply.

You’ll learn all about voltage, current, and loads in the next tutorial: Voltage, Current, Resistance, and Ohm’s Law. But for now, let’s learn about two special cases of circuit: short circuit, and open circuit. Knowing about these will help tremendously when you’re troubleshooting your own circuits.

Short Circuit

DON’T DO THIS, but if you connect a wire directly from the positive to the negative side of a power supply, you’ll create what is called a short circuit. This is a very bad idea.

This seems like the best possible circuit, so why is it a bad idea? Remember that electrical current wants to flow from a higher voltage to a lower voltage, and if you put a load into the current, you can do something useful like light up an LED.

If you DO have a load in the current, the current flow through your circuit will be limited to that which your device consumes, which is usually a very small amount. However, if you DON’T put anything in to restrict the current flow, there won’t be anything to slow down the current, and it will try to be infinite!

Your power supply can’t provide infinite current, but it will provide as much as it can, which may be a lot. This could cause your wire to burn up, damage the power supply, drain your battery, or other exciting things. Most of the time your power supply will have some sort of safety mechanism built into it to limit the maximum current in the event of a short circuit, but not always. This is the reason all homes and buildings have circuit breakers, to prevent fires from starting in the event of a short circuit somewhere in the wiring.

A closely related problem is accidentally letting too much current flow through part of your circuit, causing a part to burn up. This isn’t quite a short circuit, but it’s close. This most often happens when you use the incorrect resistorvalue, which lets too much current flow through another component such as an LED.

The bottom line: if you notice that things are suddenly becoming hot or a part suddenly burns out, immediately turn off the power and look for possible short circuits.

Open Circuit

The opposite of a short circuit is an open circuit. This is a circuit where the loop isn’t fully connected (and therefore this isn’t really a circuit at all).

Unlike the short circuit above, nothing will get hurt by this “circuit”, but your circuit won’t work either. If you’re new at circuits, it can often be hard to find where the break is, especially if you’re using breadboards where all the conductors are hidden.

If your circuit doesn’t work, the most likely cause is an open circuit. This is usually due to a broken connection or a loose wire. (Short circuits can steal all the power from the rest of your circuit, so be sure to look for those as well.)

TIP: if you can’t easily find where your circuit is open, a multimeter can be very useful tool. If you set it to measure volts, you can use it to check the voltage at various points in your powered circuit, and eventually find the point where voltage isn’t getting through.

Resources and Going Further

You’ve just learned, in its most basic form, what a circuit is. As you keep learning, you’ll encounter more complex circuits that have multiple loops and many more electronic components. But ALL circuits, no matter how complex, will follow the same rules as the basic one-loop circuit you just learned about.

Your journey into electronics is just beginning, here are some suggested next topics to explore:

Breadboards are useful tools that let you quickly build temporary circuits using jumper wires. We use them all the time. You also may want to master working with wire to help you build your circuits.

A multimeter lets you measure voltage, current, and resistance and is a great help when trying to troubleshoot malfunctioning circuits.

Circuits come in all different sizes, shapes, and configurations. Check out the series vs parallel circuits tutorial to see circuits taken to the next level.

Here are some tutorials on the most common components you’ll use when building circuits.

A great way to learn about circuits is to start making some. Our LED tutorial will show how to light up one or many LEDs.

Resistors are one of the most widely used components in circuits.

Capacitors are also found in most circuits. As are Diodes

Electric circuit,  path for transmitting electric current. An electric circuit includes a device that gives energy to the charged particles constituting the current, such as a battery or a generator; devices that use current, such as lamps, electric motors, or computers; and the connecting wires or transmission lines. Two of the basic laws that mathematically describe the performance of electric circuits are Ohm’s law and Kirchhoff’s rules.

Encyclopædia Britannica, Inc. Encyclopædia Britannica, Inc.

Electric circuits are classified in several ways. A direct-current circuit carries current that flows only in one direction. An alternating-current circuit carries current that pulsates back and forth many times each second, as in most household circuits. A series circuit comprises a path along which the whole current flows through each component. A parallel circuit comprises branches so that the current divides and only part of it flows through any branch. The voltage, or potential difference, across each branch of a parallel circuit is the same, but the currents may vary. In a home electrical circuit, for instance, the same voltage is applied across each light or appliance, but each of these loads draws a different amount of current, according to its power requirements. A number of similar batteries connected in parallel provides greater current than a single battery, but the voltage is the same as for a single battery. See also integrated circuit; tuned circuit.

The network of transistors, transformers, capacitors, connecting wires, and other electronic components within a single device such as a radio is also an electric circuit. Such complex circuits may be made up of one or more branches in combinations of series and series-parallel arrangements.

digital circuit, electronic circuit that can take on only a finite number of states. That is contrasted with analog circuits , whose voltages or other quantities vary in a continuous manner. Binary (two-state) digital circuits are the most common. The two possible states of a binary circuit are represented by the binary digits, or bits, 0 and 1. The states are also commonly referred to as "on" and "off" or "high" and "low" (see information theory ). The simplest forms of digital circuits are built from logic gates, the building blocks of the digital computer . Since most of the physical variables encountered in the real world, e.g., position and temperature, exist in analog form, they are represented electrically by continuously varying currents and voltages in analog circuits. To make digital and analog circuits compatible special converters are used—either analog-to-digital or digital-to-analog depending on the direction of information flow. Digital circuits simulate continuous functions with strings of bits; the more bits that are used, the more accurately the continuous signal can be represented. For example, if 16 bits are used to represent a varying voltage, the signal can be assigned one of more than 65,000 different values. Digital circuits are more immune to noise than analog circuits, and digital signals can be stored and duplicated without degradation (see compact disc ). Digital circuits can often manipulate signals more effectively—and less expensively—than analog circuits. Those reasons helped digital systems to succeed over all analog contenders for proposed high-definition television in the United States.

# data[].attributes.body
A circuit diagram (electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while aschematic diagram shows the components and interconnections of the circuit using standardized symbolic representations. The presentation of the interconnections between circuit components in the schematic diagram does not necessarily correspond to the physical arrangements in the finished device.[1]

Unlike a block diagram or layout diagram, a circuit diagram shows the actual electrical connections. A 21drawing meant to depict the physical arrangement of the wires and the components they connect is called artwork or layout, physical design, or wiring diagram.

Circuit diagrams are used for the design (circuit design), construction (such as PCB layout), and maintenance of electrical and electronic equipment.

In computer science, circuit diagrams are useful when visualizing expressions using Boolean algebra.[2]

Contents

[show]

Symbols[edit]

Main article: Electronic symbol

Circuit diagrams are pictures with symbols that have differed from country to country and have changed over time, but are now to a large extent internationally standardized. Simple components often had symbols intended to represent some feature of the physical construction of the device. For example, the symbol for a resistor shown here dates back to the days when that component was made from a long piece of wire wrapped in such a manner as to not produce inductance, which would have made it a coil. These wirewound resistors are now used only in high-power applications, smaller resistors being cast from carbon composition (a mixture of carbon and filler) or fabricated as an insulating tube or chip coated with a metal film. The internationally standardized symbol for a resistor is therefore now simplified to an oblong, sometimes with the value in ohms written inside, instead of the zig-zag symbol. A less common symbol is simply a series of peaks on one side of the line representing the conductor, rather than back-and-forth as shown here.

Wire Crossover Symbols for Circuit Diagrams. Note that the CAD symbol for insulated crossing wires is exactly the same as the older, non-CAD symbol for non-insulated crossing wires. To avoid confusion, the wire "jump" (semi-circle) symbol for insulated wires in non-CAD schematics is recommended (as opposed to using the CAD-style symbol for no connection), so as to avoid confusion with the original, older style symbol, which means the exact opposite. The newer, recommended style for 4-way wire connections in both CAD and non-CAD schematics is to stagger the joining wires into T-junctions.[3]

The linkages between leads were once simple crossings of lines. With the arrival of computerized drafting, the connection of two intersecting wires was shown by a crossing of wires with a "dot" or "blob" to indicate a connection. At the same time, the crossover was simplified to be the same crossing, but without a "dot". However, there was a danger of confusing the wires that were connected and not connected in this manner, if the dot was drawn too small or accidentally omitted (e.g. the "dot" could disappear after several passes through a copy machine).[4] As such, the modern practice for representing a 4-way wire connection is to draw a straight wire and then to draw the other wires staggered along it with "dots" as connections (see diagram), so as to form two separate T-junctions that brook no confusion and are clearly not a crossover.[5][6]

For crossing wires that are insulated from one another, a small semi-circle symbol is commonly used to show one wire "jumping over" the other wire[3][7][8] (similar to how jumper wires are used).

A common, hybrid style of drawing combines the T-junction crossovers with "dot" connections and the wire "jump" semi-circle symbols for insulated crossings. In this manner, a "dot" that is too small to see or that has accidentally disappeared can still be clearly differentiated from a "jump".[3][7]

On a circuit diagram, the symbols for components are labelled with a descriptor or reference designator matching that on the list of parts. For example, C1 is the first capacitor, L1 is the first inductor, Q1 is the first transistor, and R1 is the first resistor (note that this is not written as a subscript, as in R1, L1,...). Often the value or type designation of the component is given on the diagram beside the part, but detailed specifications would go on the parts list.

Detailed rules for reference designations are provided in the International standard IEC 61346

A circuit diagram (electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while aschematic diagram shows the components and interconnections of the circuit using standardized symbolic representations. The presentation of the interconnections between circuit components in the schematic diagram does not necessarily correspond to the physical arrangements in the finished device.[1]

Unlike a block diagram or layout diagram, a circuit diagram shows the actual electrical connections. A drawing meant to depict the physical arrangement of the wires and the components they connect is calledartwork or layout, physical design, or wiring diagram.

Circuit diagrams are used for the design (circuit design), construction (such as PCB layout), and maintenance of electrical and electronic equipment.

In computer science, circuit diagrams are useful when visualizing expressions using Boolean algebra.[2]

Contents

[show]

Common schematic diagram symbols (US symbols)

The circuit diagram for a four-bit TTLcounter, a type of state machine

It is a usual although not universal convention that schematic drawings are organized on the page from left to right and top to bottom in the same sequence as the flow of the main signal or power path. For example, a schematic for a radio receiver might start with the antenna input at the left of the page and end with the loudspeaker at the right. Positive power supply connections for each stage would be shown towards the top of the page, with grounds, negative supplies, or other return paths towards the bottom. Schematic drawings intended for maintenance may have the principal signal paths highlighted to assist in understanding the signal flow through the circuit. More complex devices have multi-page schematics and must rely on cross-reference symbols to show the flow of signals between the different sheets of the drawing.

Detailed rules for the preparation of circuit diagrams, and other document types used in electrotechnology, are provided in the international standard IEC 61082-1.

Relay logic line diagrams, also called ladder logic diagrams, use another common standardized convention for organizing schematic drawings, with a vertical power supply rail on the left and another on the right, and components strung between them like the rungs of a ladder.

Artwork[edit]

A rat's nest

Once the schematic has been made, it is converted into a layout that can be fabricated onto a printed circuit board (PCB). Schematic-driven layout starts with the process of schematic capture. The result is what is known as a rat's nest. The rat's nest is a jumble of wires (lines) criss-crossing each other to their destination nodes. These wires are routed either manually or by the use of electronics design automation (EDA) tools. The EDA tools arrange and rearrange the placement of components and find paths for tracks to connect various nodes. This results in the final layout artwork for the integrated circuit or printed circuit board.[9]

A generalized design flow may be as follows:

Schematic → schematic capture → netlist → rat's nest → routing → artwork → PCB development and etching → component mounting → testing

Light switch                                                                                               Doorbell

Circuit Science Projects

13

Build a Circuit

A circuit is a path that electricity flows along. It starts at a power source, like a battery, and flows through a wire to a light bulb or other object and back to other side of the power source. You can build your own circuit and see how it works with this project!

What You Need:

Small light bulb (or a flashlight bulb)

2 batteries (with the correct voltage for your light bulb)

2 alligator clip wires or aluminum foil*

Paper clips

Electrical tape (Scotch®tape also works)

Bulb holder (optional)

Battery holders (optional**)

*To use foil instead of wires, cut 2 strips each 6" long and 3" wide. Fold each one tightly along the long edge to make a thin strip.)

**To use paper clips instead of battery holders, tape one end of a paper clip to each end of your battery using thin strips of tape. Then connect your wires to the paper clips.

Part 1 - Making a Circuit:

1. Connect one end of each wire to the screws on the base of the light bulb holder. (If you're using foil, ask an adult to help you unscrew each screw enough to fit a foil strip under it.)

2. Connect the free end of one wire to the negative ("-") end of one battery. Does anything happen?

3. Attach the free end of the other wire to the positive ("+") end of the battery. Now what happens?

Part 2 - Adding Power

1. Disconnect the battery from your circuit. Stand one battery so that the "+" end is pointing up, then set the other battery next to it so that the flat "-" end is pointing up. Tape around the middle of the batteries to hold them together.

2. Set a paperclip across the batteries so that it connects the "+" end of one to the "-" end of the other. Tape the paperclip in place with a narrow piece of tape (do not tape over the metal battery ends).

3. Turn the batteries over and tape one end of a paper clip onto each of the batteries. Now you can connect one wire to each paper clip. (The bottom of the battery pack should only have one paper clip - do not connect a wire to it.)

4. Connect the free ends of the wires to the light bulb.

(Note: Instead of steps 1-3, you can use two batteries in battery holders and connect them together with one wire.)

What Happened:

In the first part, you made a simple circuit that used a battery to light up a light bulb. Batteries supply electricity. When they're connected properly, they can "power" things, like a flashlight, an alarm clock, a radio, or a timer. Why didn't the light bulb light up when you connected it to one end of the battery with a wire? Electricity from a battery has to flow out one end (the negative or "-" end) and back in through the positive ("+") end in order to work. What you built with the battery, wire, and bulb in step 3 is called an open circuit. In order for electricity to start flowing, you need aclosed circuit. Electricity is caused by tiny particles with negative charges, called electrons. When a circuit is complete, or closed, electrons can flow from one end of a battery all the way around, through the wires, to the other end of the battery. Along its way, it will carry electrons to electrical objects that are connected to it - like the light bulb - and make them work!

In the second part, you added another battery. That should have made the light bulb burn more brightly, because two batteries together can supply more electricity than just one! The paper clip across the bottom of the battery pack allowed electricity to flow between the batteries, making the flow of electrons stronger.

Do you see how closed and open circuits work to allow or stop electricity from flowing?

Insulator or Conductor?

Materials that electricity can flow through are call conductors. Materials that stop electricity from flowing are called insulators. You can find out which things around your house are conductors and which are insulators using the circuit you made in the last project to test them!

What You Need:

Circuit with light bulb & 2 batteries

Extra alligator clip wire (or aluminum foil wire*)

Objects to test (made of metal, glass, paper, wood, and plastic)

Worksheet (optional)

What You Do:

1. Disconnect one of the wires from the battery pack. Connect one end of the new wire to the battery. You should have two wires with free ends (between the light bulb and the battery pack).

2. You have made an open circuit and the bulb should not light up. Next you will test objects to see if they are conductors or insulators. If the object is a conductor, the light bulb will light up. It is is an insulator, it will not light. For each object, guess whether you think each object will complete the circuit and light up the light bulb or not.

3. Connect the ends of the free wires to an object and see what happens. Some objects you could test are a paper clip, a pair of scissors (try the blades and the handles separately), a glass, a plastic dish, a wooden block, your favorite toy, or anything else you can think of.

What Happened:

Before you test each object, guess whether it will make the light bulb light up or not. If it does, the object you're touching the wires to is a conductor. The light bulb lights up because the conductor completes, or closes, the circuit and electricity can flow from the battery to the light bulb and back to the battery! If it doesn't light up, the object is an insulator and it stops the flow of electricity, just like an open circuit does.

When you set up the circuit in step 1, it was an open circuit. Electrons could not flow all the way around because two of the wires were not touching. The electrons were interrupted. When you placed an object made of metal between the two wires, the metal closed or completed the circuit - the electrons could flow across the metal object to get from one wire to the next! Objects that completed the circuit made the light bulb light up. Those objects are conductors. They conduct electricity. Most other materials, like plastic, wood, and glass are insulators. An insulator in an open circuit does not complete the circuit, because electrons cannot flow through it! The light bulb did not light up when you put an insulator in between the wires.

If you're using wires or alligator clips, take a good look at them. Inside they are made of metal, but they have plastic around the outside. Metal is a good conductor. Plastic is a good insulator. The plastic wrapped around the wire helps keep electrons flowing along the metal wire by blocking them from transferring to other object outside of the wires

Circuit Diagram

A circuit diagram is a visual display of an electrical circuit using either basic images of parts or industry standard symbols. Symbol usage depends on the audience viewing the diagram. These two different types of circuit diagrams are called pictorial (using basic images) or schematic style (using industry standard symbols). A schematic style circuit diagram is used to give a visual representation of an electrical circuit to an electrician. The pictorial style circuit diagram would be used for a broader, less technical audience.

Symbols Used in Circuit Diagrams

There are hundreds of different symbols that can be used in a circuit diagram. These include simple images of objects such as a battery or a resistor for a pictorial style circuit diagram, or industry-standard symbols for objects such as capacitors or inductors.

In conjunction with circuit diagram symbols, there are also a series of different types of line styles to connect objects. In the event lines cross, use line hops to show wire crossover. It is important to understand who will be viewing the circuit diagram to ensure use of the correct types of symbols.

How to Create a Circuit Diagram

There are many different ways to create a circuit diagram. They can be created manually, but the more efficient way is to use diagramming software such as SmartDraw, which is designed for this purpose. Diagramming software that is specifically designed for creating a circuit diagram offers several advantages.

It is fast and allows for simple construction.

It provides access to thousands of symbols.

It is easy to share electronically.

It provides precise placement of objects.

It is easy to edit.

SmartDraw allows you to quickly, accurately, and easily create a circuit diagram. It also allows you to create personal custom libraries of symbols you commonly use.

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow

Overview

Welcome to circuits 101! One of the first things you’ll encounter when learning about electronics is the concept of a circuit. This tutorial will explain what a circuit is, as well as discuss voltage in further detail.

A simple circuit, involving a button, an LED, and a resistor, built two different ways.

Suggested Reading

There are a few concepts you should have a good understanding of to help you get the most out of this tutorial.

What is Electricity?

Electric Power

Voltage, Current, Resistance, and Ohm’s Law

Alternating Current (AC) vs Direct Current (DC)

Polarity

Circuit Basics

Voltage and How it Works

You’ve probably heard that a battery or a wall outlet has a certain number of volts. This is a measurement of the electrical potential produced by the battery, or the utility grid connected to the wall outlet.

All those volts are sitting there waiting for you to use them, but there’s a catch: in order for electricity to do any work, it needs to be able to move. It’s kind of like a blown-up balloon; if you pinch it off, there is air in there thatcould do something if it’s released, but it won’t actually do anything until you let it out.

Unlike air coming out of a balloon, electricity can only flow through materials that can conduct electricity, such as copper wire. If you connect a wire to a battery or wall outlet (WARNING: the voltage in a wall outlet is dangerous, don’t do this!), you will be giving the electricity a path to follow. But if the wire isn’t connected to anything else, the electricity won’t have anywhere to go and still won’t move.

What makes electricity move? Electricity wants to flow from a higher voltage to a lower voltage. This is exactly like the balloon: the pressurized air in the balloon wants to flow from inside the balloon (higher pressure) to outside the balloon (lower pressure). If you create a conductive path between a higher voltage and a lower voltage, electricity will flow along that path. And if you insert something useful into that path like an LED, the flowing electricity will do some work for you, like lighting up that LED. Huzzah!

So, where do you find a higher voltage and a lower voltage? Here’s something really useful to know: every source of electricity has two sides. You can see this on batteries, which have metal caps on both ends, or your wall outlet that has two (or more) holes. In batteries and other DC (Direct Current) voltage sources, these sides (often calledterminals) are named positive (or “+”), and negative (or “-”).

Why does every source of electricity have two sides? This goes back to the idea of “potential”, and that you need a voltage difference in order to get electricity to flow. It sounds silly, but you can’t have a difference without two things to be different. In any power supply, the positive side will have a higher voltage than the negative side, which is exactly what we want. In fact, when we measure voltage, we usually say that the negative side is 0 volts, and the positive side is however many volts the supply can provide.

Electrical sources are like pumps. Pumps always have two sides, an outlet that blows something out, and an inlet that sucks something in. Batteries and generators and solar panels work the same way. Something inside them is hard at work moving electricity towards the outlet (the positive side), but all that electricity leaving the device creates a void, which means that the negative side needs to pull electricity in to replace it.*

What have we learned so far?

Voltage is potential, but electricity needs to flow to do anything useful.

Electricity needs a path to flow through, which must be an electrical conductor such as copper wire.

Electricity will flow from a higher voltage to a lower voltage.

DC voltage sources always have two sides, called positive and negative, with the positive side a higher voltage than the negative side.

The Simplest Circuit

We’re finally ready to make electricity work for us! If we connect the positive side of a voltage source, through something that does some work such as a Light Emitting Diode (LED), and back to the negative side of the voltage source; electricity, or current, will flow. And we can put things in the path that do useful things when current flows through them, like LEDs that light up.

This circular path, which is always required to get electricity to flow and do something useful, is called a circuit. A circuit is a path that starts and stops at the same place, which is exactly what we’re doing.

Click this link to see a simulation of current flowing through a simple circuit. This simulation requires Java to run.

*Benjamin Franklin originally wrote that electricity flows from the positive side of a voltage source to the negative side. However, Franklin had no way of knowing that electrons actually flow in the opposite direction - at the atomic level, they come out of the negative side and loop back to the positive side. Because engineers followed Franklin’s lead for hundreds of years before the truth was discovered, we still use the “wrong” convention to this day. Practically speaking this detail doesn’t matter, and as long as everyone uses the same convention, we can all build circuits that work just fine.

Short and Open Circuits

What is a “Load”?

The reason we want to build circuits is to make electricity do useful things for us. The way we do that is by putting things in the circuit that use the current flow to light up, make noise, run programs, etc.

These things are called loads, because they “load down” the power supply, just like you’re “loaded down” when you’re carrying something. The same way you could be loaded down with too much weight, it’s possible to load down a power supply too much, which will slow down the current flow. But unlike you, it’s also possible to load down a circuit too little - this may let too much current flow (imagine running too fast if you weren’t carrying any weight), which can burn out your parts or even the power supply.

You’ll learn all about voltage, current, and loads in the next tutorial: Voltage, Current, Resistance, and Ohm’s Law. But for now, let’s learn about two special cases of circuit: short circuit, and open circuit. Knowing about these will help tremendously when you’re troubleshooting your own circuits.

Short Circuit

DON’T DO THIS, but if you connect a wire directly from the positive to the negative side of a power supply, you’ll create what is called a short circuit. This is a very bad idea.

This seems like the best possible circuit, so why is it a bad idea? Remember that electrical current wants to flow from a higher voltage to a lower voltage, and if you put a load into the current, you can do something useful like light up an LED.

If you DO have a load in the current, the current flow through your circuit will be limited to that which your device consumes, which is usually a very small amount. However, if you DON’T put anything in to restrict the current flow, there won’t be anything to slow down the current, and it will try to be infinite!

Your power supply can’t provide infinite current, but it will provide as much as it can, which may be a lot. This could cause your wire to burn up, damage the power supply, drain your battery, or other exciting things. Most of the time your power supply will have some sort of safety mechanism built into it to limit the maximum current in the event of a short circuit, but not always. This is the reason all homes and buildings have circuit breakers, to prevent fires from starting in the event of a short circuit somewhere in the wiring.

A closely related problem is accidentally letting too much current flow through part of your circuit, causing a part to burn up. This isn’t quite a short circuit, but it’s close. This most often happens when you use the incorrect resistorvalue, which lets too much current flow through another component such as an LED.

The bottom line: if you notice that things are suddenly becoming hot or a part suddenly burns out, immediately turn off the power and look for possible short circuits.

Open Circuit

The opposite of a short circuit is an open circuit. This is a circuit where the loop isn’t fully connected (and therefore this isn’t really a circuit at all).

Unlike the short circuit above, nothing will get hurt by this “circuit”, but your circuit won’t work either. If you’re new at circuits, it can often be hard to find where the break is, especially if you’re using breadboards where all the conductors are hidden.

If your circuit doesn’t work, the most likely cause is an open circuit. This is usually due to a broken connection or a loose wire. (Short circuits can steal all the power from the rest of your circuit, so be sure to look for those as well.)

TIP: if you can’t easily find where your circuit is open, a multimeter can be very useful tool. If you set it to measure volts, you can use it to check the voltage at various points in your powered circuit, and eventually find the point where voltage isn’t getting through.

Resources and Going Further

You’ve just learned, in its most basic form, what a circuit is. As you keep learning, you’ll encounter more complex circuits that have multiple loops and many more electronic components. But ALL circuits, no matter how complex, will follow the same rules as the basic one-loop circuit you just learned about.

Your journey into electronics is just beginning, here are some suggested next topics to explore:

Breadboards are useful tools that let you quickly build temporary circuits using jumper wires. We use them all the time. You also may want to master working with wire to help you build your circuits.

A multimeter lets you measure voltage, current, and resistance and is a great help when trying to troubleshoot malfunctioning circuits.

Circuits come in all different sizes, shapes, and configurations. Check out the series vs parallel circuits tutorial to see circuits taken to the next level.

Here are some tutorials on the most common components you’ll use when building circuits.

A great way to learn about circuits is to start making some. Our LED tutorial will show how to light up one or many LEDs.

Resistors are one of the most widely used components in circuits.

Capacitors are also found in most circuits. As are Diodes

Electric circuit,  path for transmitting electric current. An electric circuit includes a device that gives energy to the charged particles constituting the current, such as a battery or a generator; devices that use current, such as lamps, electric motors, or computers; and the connecting wires or transmission lines. Two of the basic laws that mathematically describe the performance of electric circuits are Ohm’s law and Kirchhoff’s rules.

Encyclopædia Britannica, Inc. Encyclopædia Britannica, Inc.

Electric circuits are classified in several ways. A direct-current circuit carries current that flows only in one direction. An alternating-current circuit carries current that pulsates back and forth many times each second, as in most household circuits. A series circuit comprises a path along which the whole current flows through each component. A parallel circuit comprises branches so that the current divides and only part of it flows through any branch. The voltage, or potential difference, across each branch of a parallel circuit is the same, but the currents may vary. In a home electrical circuit, for instance, the same voltage is applied across each light or appliance, but each of these loads draws a different amount of current, according to its power requirements. A number of similar batteries connected in parallel provides greater current than a single battery, but the voltage is the same as for a single battery. See also integrated circuit; tuned circuit.

The network of transistors, transformers, capacitors, connecting wires, and other electronic components within a single device such as a radio is also an electric circuit. Such complex circuits may be made up of one or more branches in combinations of series and series-parallel arrangements.

digital circuit, electronic circuit that can take on only a finite number of states. That is contrasted with analog circuits , whose voltages or other quantities vary in a continuous manner. Binary (two-state) digital circuits are the most common. The two possible states of a binary circuit are represented by the binary digits, or bits, 0 and 1. The states are also commonly referred to as "on" and "off" or "high" and "low" (see information theory ). The simplest forms of digital circuits are built from logic gates, the building blocks of the digital computer . Since most of the physical variables encountered in the real world, e.g., position and temperature, exist in analog form, they are represented electrically by continuously varying currents and voltages in analog circuits. To make digital and analog circuits compatible special converters are used—either analog-to-digital or digital-to-analog depending on the direction of information flow. Digital circuits simulate continuous functions with strings of bits; the more bits that are used, the more accurately the continuous signal can be represented. For example, if 16 bits are used to represent a varying voltage, the signal can be assigned one of more than 65,000 different values. Digital circuits are more immune to noise than analog circuits, and digital signals can be stored and duplicated without degradation (see compact disc ). Digital circuits can often manipulate signals more effectively—and less expensively—than analog circuits. Those reasons helped digital systems to succeed over all analog contenders for proposed high-definition television in the United States.