[sdiy] What's the best freeware schematic capture and PCB layout software

[brianw]

I agree that archiving an image of the original schematic is a good idea, even if you also capture the schematic in software.

I recommend a flat bed scanner and grayscale (unless the original is actually color) and then post-process to optimize the image for archival. A flatbed will keep the paper flat and the schematic in focus in all areas. Scan at the native resolution of the scanner, and archive that original before processing, so you have the option of re-doing the processing if there's an issue.

Unless you have a photography studio with a stand for your camera, designed for photographing flat documents (or other printed image), taking photos will end up distorting the image.

If the original is two-sided, then a trick that I came up with is to scan with a black background, rather than a white background, so that any image printed on the back of the sheet will not stand out. You have to use post-processing to remove the faint gray bleed-through, but at least the ink on the back side blends in with the black background, so it's easy to pick a threshold so that the light gray becomes pure white. My new flatbed scanner has a feature that you can enable to "reduce bleed-through" but I have not tested whether that works better than my old techniques. Of course, if the original is only printed on one side then you don't have to worry about this particular aspect.

Neither the original scan nor any of the processed copies should be using JPEG format. JPEG is designed for continuous tone images of real-world objects, but JPEG is horrible for hard-edged graphics like schematics. In my opinion, the worst thing is to scan an ancient schematic and then use JPEG for the file, because there are fringes around every line that often make the details illegible.

Proper file formats are TIFF, GIF, PNG, or any bitmap that doesn't use lossy compression.

Once the bleed-through has been eliminated, it's usually possible to convert from grayscale to black-and-white, which will reduce the image size. Grayscale is one-third the size of color, and B&W is 1/8 of grayscale (or 1/24 of color). From there, fax compression actually works quite well, and often ends up smaller than a JPEG but without the horrible fringes.

In some cases, I find that I need to maintain grayscale so that the text is legible. If things look smoother in grayscale than in B&W, I'll maintain grayscale. Even in the tough cases, though, it make still be legible if the grayscale is reduced from 8-bit to fewer bits. Scanning at a higher resolution usually makes it easier to remain legible in B&W mode. If the text gets too chunky, then keep some grayscale for smooth curves.


As for schematic capture software, I licensed Eagle when it was the only viable option for Mac OS X. Since then, KiCAD has become viable. Eagle exports to Gerber files, which are the industry standard. Some PCB fabrication houses actually take Eagle files. I like the way Eagle separates the symbol (transistor) from the package (through-hole versus surface-mount). This allows you to keep the look of the schematic completely independent of the layout and parts selection process. I've even started a project as SMD, only to go back and convert to through-hole, and Eagle allowed me to keep the schematic the same. I just had to re-do the layout. Eagle has an open source library of packages and symbols, but you do have to double-check everything. You can easily create your own, or fix the errors in the public domain ones. The licensing model for Eagle is currently subscription (I think), so I would not recommend getting into an ongoing expense. I realize that you asked for 'free' but sometimes it's worth spending a little money to get a tool that is reasonably well-supported.

Brian


On May 12, 2024, at 3:21 PM, Donald Tillman wrote:
> Hi Dana,
> 
> I'll suggest just photographing them, and tweaking the brightness-level curves for readability. 
> 
> Transcribing them to a CAD package might be error prone, a lot of work, and dependent on parts libraries.  And photographs preserve the historical context and all.
> 
> I'm sure folks here will provide all sorts of recommendations based on their experiences... 
> 
> One metric I would use is: Can it produce publication quality art?  Because I care a lot about that.
> 
> I use the Gnu gEDA gschem package, with my own parts libraries, and it can provide publication quality art.
> 
> (I've never seen a KiCad schematic that doesn't look like crap.  But hey, I'm persuadable; maybe someone has a counterexample.)
> 
>   -- Don
> 
> On May 12, 2024, at 1:39 PM:
>> Hi,
>> I have a number of 45 year old blue line schematics that I want to capture on the computer before they disintegrate or fade away entirely from age.
>> Using search engine, I see a number of freeware schematic and PCB layout packages available.
>> Is the any consensus here as to what is the best software to use?
>>  
>> I downloaded the first package I came across (KiCad). I wonder if something else might be better.
>> Any thoughts?
>>  
>> Dana