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What's the difference between a schematic, a block diagram, a wiring diagram and a PCB layout?

Why do engineers want a schematic instead of a wiring diagram?

Where does Fritzing fit into this?

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Thank you for taking the time to do this. –  Dave Tweed Apr 2 at 23:00
    
Once you see why we want schematics as apposed to other types of diagrams, see also electronics.stackexchange.com/q/28251/4512 for how to draw schematics properly. –  Olin Lathrop Apr 3 at 12:43

3 Answers 3

up vote 28 down vote accepted

Schematic

A schematic shows connections in a circuit in a way that is clear and standardized. It is a way of communicating to other engineers exactly what components are involved in a circuit as well as how they are connected. A good schematic will show component names and values, and provide labels for sections or components to help communicate the intended purpose. Note how connections on wires (or "nets") are shown using dots and non-connections are shown without a dot.

Schematic

Block Diagram

A block diagram shows a higher level (or organizational layout) of functional units in a circuit (or a device, machine, or collection of these). It is meant to show data flow or organization between separate units of function. A block diagram gives you an overview of the interconnected nature of circuit assemblies or components.

Block Diagram

Wiring Diagram

A wiring diagram is sometimes helpful to illustrate how a schematic can be realized in a prototype or production environment. A proper wiring diagram will be labeled and show connections in a way that prevents confusion about how connections are made. Typically they are designed for end-users or installers. They focus on connections rather than components.

Wiring Diagram

PCB Layout

A PCB Layout is the resulting design from taking a schematic with specific components and determining how they will physically be laid out on a printed circuit board. To produce a PCB Layout, you must know the connections of components, component sizes (footprints), and a myriad of other properties (such as current, frequencies, emissions, reflections, high voltage gaps, safety considerations, manufacturing tolerances, etc.).

PCB Layout

Fritzing

Fritzing is a popular open-source software program designed to help you create electronics prototypes. It uses a visual approach to allow you to connect components to Arduino using a virtual breadboard, and even provides ways to design a PCB. Its strength is in the ease with which new users can approach it. One of the principal working views is the virtual breadboard:

Fritzing diagram

However, as you can see, it can be time-consuming to tell exactly how components are connected, even if you are very familiar with how breadboard connections work (as most electronics engineers are). As a circuit gets more complex, the visualization becomes more cluttered.

Fritzing provides a way to produce a schematic:

Fritzing screenshot

Be sure to use this to produce a schematic if you need to ask questions about your circuit. It will help others to quickly understand the components and connections involved in your design.

Prototype Photo

Sometimes a photo can help engineers troubleshoot your design. Especially if quality issues are suspected, such as soldering reliability, improper connections, incorrect polarities, and other problems which might be revealed in a photo. However, realize that most photos are not immediately useful, and if your project is complicated, a picture will do little more than show that you've spent a lot of time and effort on your project! Hint: Not helpful!

Breadboard complicated build

Images were obtained using internet image searches with license set to public domain or free to use for non-commercial use.

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Why we prefer schematics, also, is that schematics contain certain idioms. For instance, a long-tailed-pair differential input stage could be drawn in a hundred different ways, ninety-five-and-a-half of which don't look anything like a long-tailed-pair differential input stage. Out of a hundred wiring diagrams, nary a single one will say "I am obviously a long-tailed pair differential input stage". –  Kaz Apr 2 at 22:12
    
@Kaz I posted this as a reference to help new users understand the differences between these diagrams. I agree that component arrangement on a schematic is important, but that's probably best omitted for the intended basic introduction level. –  JYelton Apr 2 at 22:14
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Then there are also bad schematics that contain elements of circuit diagrams. –  Phil Frost Apr 3 at 1:18
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@Passerby It's not exactly easy to find equal versions using free images. I obtained Fritzing with the idea of creating my own images instead of looking for others, but I didn't have time to really get into it. I admit bias because I prefer schematics for communicating circuit designs. (I think many other members of the community would agree.) Feel free to supply your own answer with bias-free diagrams. –  JYelton Apr 3 at 5:07
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@Passerby: The schematics for the system in that block diagram would take many pages (but still be usable), and a "wiring diagram" for the system would be an impenetrable rats' nest. That's not a skew aimed against Fritzing diagrams, it's reality. –  Ben Voigt Apr 3 at 21:24

Compare Apples to Apples. Every Type of Diagram Is harder to read the more complex it becomes, not just fritzing

Comparable Schematic:

enter image description here

Comparable Wiring Diagrams:

enter image description here

enter image description here

Comparable Block Diagram:

enter image description here

Comparable PCB Layouts:

enter image description here

enter image description here

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Actually, JYelton's images were more consistent in circuit complexity that yours are. His had about the same number and size of ICs and many fewer discretes on the wiring diagram. While yours are the same visual complexity as each other, but the block diagram has much MUCH more complexity, and the schematic has a lot more circuitry documented than the remaining ones. Which is pretty much the point. –  Ben Voigt Apr 3 at 21:22
    
@BenVoigt because a single ic schematic or straight wiring is consistent with an arduino + quad motor driver + motors + rtc + battery backup + buzzer? –  Passerby Apr 3 at 22:46
    
Guess I was thinking of the connection to the Arduino as a connector, and not the entire Arduino. (The Fritzing diagram doesn't show the topology of the Arduino either). Actually it probably should be equated to four distinct connectors on the schematic... since the Fritzing diagram does distinguish four connectors. So that would add a little to the schematic complexity. Still quite close. A schematic would represent connections to motors and buzzers as two pin connectors, for which the two-pad discretes are a good standin. –  Ben Voigt Apr 3 at 22:54

The purpose of a schematic, generally speaking, is to show those aspects of something which are most relevant to understanding it, at the expense of changing details which are less relevant. For electrical schematics, the biggest thing that's omitted is an accurate sense of physical layout, but schematics may also omit certain forms of "regular" wiring (as a common historical example, if a device had ten vacuum tubes with filaments wired in series, and the filaments didn't connect to anything else, a note saying how the filaments were connected would be more meaningful than would be lines on the schematic connecting them together). Additionally, schematics may sometimes indicate that a certain sub-circuit should be repeated some number of times, possibly with some slight variation. It may not be possible to build a device with such orderly repetition (e.g. a device may have four groups of six subcircuits, but the shape of the available space may require the subcircuits be laid out in a 5x5 grid) but someone reading the schematic generally won't care about the physical arrangement.

It's interesting to note that while "schematics" are most often used with electric/electronic circuit designs, the same principles can also be applied to fields like plumbing or even cartography. Modern subway "maps" are functionally more like circuit diagrams than maps, giving more attention how stations are connected than to their actual locations--an innovation which debuted with Henry C. Beck's 1931 map of the London Underground.

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