I am looking for a good free online or offline tool to draw processor schematics like this: enter image description here

Further characteristics:

  • If it is not an online tool it could be for linux or windows but online would be preferred
  • I want to use it to draw independent chematics (no logic behind needed)
  • The elements should be placed manually (drag & drop)
  • The program should have elements for processor / logic modulation like in the example picture

Lucidchart for example is relativly close to what I am looking for but in the free version very limited and does not have the needed elements.

  • For what operating system? Is this to draw one-off schematics or do they need to be batch-modifiable? Do you want manual or automatic control over element placement? Do you need custom elements? Commented Sep 27, 2014 at 12:12
  • @Gilles I tried to specify my request a bit.
    – kimliv
    Commented Sep 27, 2014 at 12:37

3 Answers 3


Xfig is a free schematic drawing software that has a variety of tools and object libraries. Among these are:

  • Electronic Physical - symbols for creating electronic wiring diagrams or layouts
  • Electronic Schematic - symbols for creating electronic schematics

I think your diagram is a combination of these two. The components can be loaded from this button enter image description here

Meeting your requested characteristics:

  • Runs on Linux, and can be installed on Windows through Cygwin/X
  • Only for drawing schematics. No logic needed
  • Elements can be loaded from libaries and moved around with drag/drop
  • The object libraries might not have all the elements you need, but it's not difficult to create your own objects
  • I will try it. An online tool would be a bit better since we are working in a group on it.
    – kimliv
    Commented Sep 28, 2014 at 0:02

This is an old question, but sharing what I found recently (Nov 2021).

First of all, there are no CPU Design only options. There are general technical drawing options and most of them are usable, but with some difficulties i.e. without the exact shapes for adders, no good connectors etc.

But with some patience I think you can use them all but the 2 free ones I think are the best are - Inkscape and Libreoffice Draw. Visio is a good one if you can afford it.

Inkscape is very nice to draw shapes and use generally. Only problem is with connectors and there is some work going on to make custom placeable connectors to make this work better. This thread has more details and this page is the issue page.

But if you scroll down in the comments, someone mentioned that Libreoffice Draw works well and they've described how to use it with an example as well:

LibreOffice Draw has gone some way towards implementing the features described above. However, they do not support connecting to the connection points of children within a group, meaning you must un-group, make a connection, then re-group in order to edit diagrams like the one below (each named port is a text-box with a dedicated connection point, which are all grouped together with the block symbol). While LibreOffice appears to be a step or two ahead of Inkscape with respect to connection points, I find Inkscape to be far superior in many other ways. If Inkscape could implement this feature, it would become my preferred drawing tool for all diagrams. enter image description here

I gave Libreoffice Draw a try, but I prefer Inkscape interface more as I'm used to it.

Here's a first attempt at making a schematic, I had to create the shapes and the connections using Bezier tool with the Ctrl key pressed. It takes a bit of time, but I think it might be better than drawing on a paper (which is what I've been using!)

enter image description here


You may want to take a look at Scheme-it. Regarding the points you mentioned above:

  • it is a (free), online tool;
  • doesn't care about the logic;
  • it uses drag'n'drop;
  • it has different level "views".

(It allows you to work with multiple pages and export your design in different formats - PNG or PDF.)

Caveat: you may need to customize some of the components (place them on the workspace and right-click to Edit them). I don't know whether this is a deal-breaker for you or not. For example, I wasn't able to locate the adders in the scheme you attached.

  • I would appreciate an explanation for the downvote, as I am sure I missed something. Commented Oct 4, 2014 at 10:22

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