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I would like to be able to scan circuit diagrams into a circuit simulator. While I am aware that symbols are not entirely standardized, is there any software that will do an approximation of this?

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  • \$\begingroup\$ @Joe - What components do you want to scan in? It might be possible to get netlists, and auto-detect resistors/caps/power/ground, but so many symbols are created by hand, vary from library to library, or edited that I'm not sure that the software could ever do anything really useful. If you want to move the schematic into a simulator, get it in digital format, and write a converter. What (legal) examples can you give where you have paper schematics but not digital ones? \$\endgroup\$ – Kevin Vermeer Sep 23 '11 at 17:34
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    \$\begingroup\$ why would it be illegal to scan, say, a circuit diagram from an audio mixing board? These are frequently supplied with the manual and are fairly, if not exhaustively detailed. \$\endgroup\$ – Joe Stavitsky Sep 23 '11 at 17:49
  • \$\begingroup\$ In fact, aside from proprietary documents and college textbooks, could you give an example of a schematic that would be illegal to scan? I can't see how a college textbook would be illegal, even, if I don't scan the whole thing. \$\endgroup\$ – Joe Stavitsky Sep 23 '11 at 17:52
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    \$\begingroup\$ Schematics can be copyrighted... but honestly I can't (right now) think of a schematic someone would show you that they didn't want you to use. If they didn't want you to have the information in the schematic they wouldn't let you see it. There is an interesting question of whether it is simply the printed example of the schematic that is copyrighted or 'derivative works' such as a netlist... or whether a netlist counts as a derivative work. However, if you are doing this to steal circuits you only have on paper with little additional effort... shame on you! \$\endgroup\$ – AngryEE Sep 24 '11 at 16:32
  • \$\begingroup\$ I believe the relevant term is "patent". However, I have no interest in stealing them, just understanding them. \$\endgroup\$ – Joe Stavitsky Sep 26 '11 at 12:47
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There unfortunately is no such software that I am aware of. It is highly unlikely that anyone will ever bother to (outside of perhaps an academic exercise) because:

  • Schematic symbols are completely non-standard, except for vague de-facto standardization for some passive and analog components, and even this isn't always followed well. Digital components are almost always just rectangles. The symbols for connectors and such are even more varied.
  • There is no standard schema for where schematics put meta-information about parts' attributes, properties, etc -- instead this often relies on a human "reading between the lines", or falling back on extra information contained in a bill-of-materials or an electronic version.
  • Most modern schematics are highly abstract-graphical, deeply hierarchical, and use feature such as split symbols that a scanning tool would not be able to reconstruct in any meaningful way (sometimes humans can barely do it).
  • Unlike OCR, one tiny mistake in a scanned schematic can have major consequences to the entire circuit. This means that a human is going to have to manually verify the schematic once imported, which is about the same amount of work as entering a schematic in the first place.

The bottom line is that schematics are a non-standard, hybrid textual-graphical representation that is barely (and sometimes not quite) good enough for a skilled human engineer to do something with.

Here is probably the closest you are going to get:

  1. Scan in your paper schematic with a scanner to an image file.
  2. Load up a new schematic in gEDA's gschem.
  3. Select Add->Picture and pick your file.
  4. Select the entire schematic page to put the image down as a picture.
  5. Draw your "real" schematic on top of it, using it as a reference.

Of course, you can do something similar with any decent schematic drawing program, not just gschem.

Alternatives:

  • Skip the scanning step, and redraw the schematic manually.
  • Directly enter the netlist information into a textual format such as a SPICE netlist or a PHDL design.
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    \$\begingroup\$ excellent response, excellent avatar. I would be happy with something that just puts down the traces. \$\endgroup\$ – Joe Stavitsky Oct 10 '11 at 15:19
  • \$\begingroup\$ @JoeStavitsky, and this goes for others also, I know Kellenjb did work on attempting to make something like this, you could check his progress or see if he reached any hurdles. He is in chat relatively regularly. \$\endgroup\$ – Kortuk Oct 10 '11 at 15:29

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