When you submit a question on the forum you will usually need to add a schematic (circuit diagram).
The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy.
Having created the image all you need to do is :
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Save the image somewhere convenient - maybe your desktop
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Start your post, and place the cursor (insertion point) where you want the image to be shown;
3: click the "upload" arrow, and
4: select your image file.
DONT upload it to Dropbox, google drive, etc. and post a link.
If you follow these simple instructions the diagram or picture will be shown in your post - as the images below are in this tutorial.
Now lets create a schematic.
To begin you must know at least SOME of the standards and symbols you will need.
A great start is to watch this video.
After watching you could visit this site that has loads of information especially suitable for beginners; and in particular a really nice list of the most commonly used symbols
You can also learn a LOT by learning to read schematics others have made.
Lets get started making an image for a schematic you can post.
Fritzing (see below) or a photo of your layout aren’t really satisfactory, especially if it has more than a few components.
Many advocate starting by drawing on paper and submitting an image. Here is a typical example. Its readable.
However there are disadvantages to this approach; if you don’t KNOW the right symbol you have no clue what to use to represent the component.
IMPORTANT
The "schematic" above lacks some important information. We have no way of knowing exactly what the "funny diode" is supposed to be.
In addition to the drawing, the schematic should also have
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A TITLE - so we know what its supposed to do; and
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Details of any "unusual" components like the "funny diode"
Its best if you can provide LINKS to the data sheet or supplier in your post.
Schematic drawing applications
There are many apps that are very easy to use for beginners and can make nice clear *standards-compliant schematics. The main purpose of this tutorial is to introduce you to some that are particularly easy to use.
Both of these will give a useful introduction to more capable (and complicated) apps such as Autodesk Eagle.
* Standards compliant? There are currently TWO important (and different) standards - the ANSI/IEEE ( Y32.2 1975 )symbols used in America and Canada, and IEC60617 used in many other countries (eg UK & Europe)
Of course they are different. It doesnt help that the standards bodies dont make them freely available.
Diagram Designer
The first schematic app I have used for many years is Diagram Designer - get it here. You will also need the "Electronic Symbols" libraries Here is an example of me using it to make a diagram.
I start by placing my main component - such as the arduino. The standard symbol for complex circuits is a simple box. Then I add more components, the wires to connect them, and finally the labels.
Remember, where you can, INPUTS go to the left, OUTPUTS to the right, positive voltages to top and negative to bottom.
Its an old package and the libraries are very limited but does produce good clear diagrams.
TinyCAD (see reply #10) is ALMOST as easy to use, and has a lot more symbols; and lots of instruction files and videos, so you may wish to skip Diagram Designer and move straight to that.
Circuit Diagram (online app)
For more complex circuits a web-based package "circuit-diagram" has a big library of components - including the arduino and rasperry pi modules, and produces nice diagrams.
Components show values and optionally designators – eg VR1. To add random text you need to search for the “label” component.
The component shows pin numbers in their physical place on the module. This is NOT standards compliant for your diagram, (as in not always flowing left to right input -> output) but can be helpful when assembling the final circuit. Compare this diagram with the diagram (Fig4) above to see the difference. Its the SAME circuit.
To place the input (potentiometer VR1) at the left I've needed to run a wire across others. Notice that wires CROSSING dont have a dot, wires JOINING do.
More good resources:
Units & Symbols for Electrical & Electronic Engineers - Ebook covering all important standards
and of course wikipedia