It’s rare when small manufacturers DIY create PCB designs. They just replicate the successful products of their competitors and make minor adjustments. Reverse engineering a schematic from a circuit board is this very process for retrieving a design and putting it into use.
Designing a high-quality PCB is a complex, technologically advanced technique. So, it’s hardly possible to replicate a schematic successfully without having instructions.
Good news: PadPCB has got you covered as we prepared a simple, step-by-step guide. It fully derives from our practical experience.
Having plenty of time and patience will be an extra benefit.
Before proceeding with photos, you should prepare a PCB board to be filmed. Clean it with a paintbrush to remove specks of dirt, dust, hairs, etc., as they will reduce the quality of images taken.
Then, adjust the lighting. It should not cause reflections. Besides, select a plain and contrasting background. It will be easier to separate a PCB board from it.
Then, take photos in a way there is no perspective, and the frame is completely filled. Take pictures of both sides of the board (component, and pattern sides). The most important nuance is that the tracks are in focus. Probably, you may consider taking photos of a board’s sections instead.
It does not seem to be complicated. But here are the tips to consider.
Flip the solder side of the board so it matches the component side. Then, set up a vertical or a horizontal guide and rotate images so the board (ground plane) is aligned all the way down.
Then, get rid of all the unnecessary elements in the photo like projecting connectors, blurs, and artifacts. Use rectangle and ellipse selection and delete tools/brushes or clone tools. Eventually, you should obtain a clear picture. Finally, save it in .png format for other software to properly read it.
The first thing you need to be retrieved in the digital format is the picture of holes/solder pads. This will help you to align the images taken and eliminate holes from the images late for the sake of traces.
As an option, you may create a topmost layer in your image editor, and turn off the green and blue channels. In case this did not help to make holes and pads visible, reduce the saturation (hue level). Then just paint the holes with a brush tool.
Once you are finished with painting holes and pads you may delete the layer below (one with the image of a PCB), so you have clear images of holes (in the form of dots) available.
You may need to experiment with settings, brush tools, layers, etc. In any case, you should receive an accurate vector image of holes and pads. Then, save it in .png format once again. You should receive something similar to the image below.
Run Autotrace and open your ground plane image. Turn on the center-line mode. In this mode, Autotrace makes PCB track pads into little loops. We need to delete the ground layer, for which connective pads need to be determined and marked. Here’s the manual way to do this in Autotrace software:
Then, open the file with the same ground plane and create a topmost layer. Use the round brush to dot a circle around every hole (ones that are plated through the ground plane). Copy the alignment marks to the layer, remove the visibility, and save this copy to a new .png file.
You should receive something similar to the image below.
After that, you need to mark “free holes.” These are pads that do not seem to be connected with anything. Probably, they just terminate the plating going from the opposite board side. Mark holes with “+” or “x” brushes.
Repeat the procedure for ground-plane holes with the brush left unused. The center of any mark will show where the holes go. After you finished, copy the alignment marks to the layer, and save the combined copy with round, “x” and “+” symbols into a new .png file.
In case you’re dealing with a single-layer board, there is not much difference between a ground plane and the substrate. You can remove marked free holes and ground-plane holes directly.
However, if you need to replicate a 4 layer board, there are internal layers as well. They are likely to be ground and power planes. In such a case, you will need the help of a continuity tester to track the hidden traces and remove ground planes properly further.
Use the fuzzy select tool or any other instrument and select the ground plan area. Grow the selection by 2 pixels. Use: Select – Grow, and save the selection made to a new channel. Make sure you did not look at a bit of a trace.
You should receive something similar to the image below.
Now, you need those tracks to have clean edges and a smooth color to help the AutoTrace program proceed with these correctly. Follow these steps:
After all is done, you probably have light gray tracks on a dark background. But AutoTrace needs a direct opposite. Follow these steps to fix it:
You need to burn out unnecessary background details that are too gray and darken the details on the tracks that are too light. Follow these steps:
Eventually, the entire background must be all white and traces all black. If there are any artifacts, just paint them white or black respectively with a brush tool.
You should receive something similar to the image below.
Your traces are now quite rough. So, you need to smooth them. For this, you need to trace the image in a vector editor program (Inkscape). Follow these steps:
Here is the most essential step of the entire process. Use AutoTrace to convert fixed lines into moveable and connectible lines. For the exact sequence of actions, you should read manuals from the program developers themselves.
Some general tips are to run conversion several times as the tracing tool may proceed exactly the same time differently.
After you receive the desired attempt (you may check how good it is by uploading it in Inkscape) you should add the layer to the drawing. Then, merge it into the picture of the holes (the one received in the early steps). Use break apart and snap tools to fix broken sections and save the end file.
You should receive something similar to the image below.
Actually, you may perform exactly the same stages as described for this side as well. But here is one more layer of complexity that should be detailed.
The details here are too fine. So the manipulation of the entire image is unlikely to bring sufficient results. So, you need to have an actual board, magnifying glass, and continuity tester. Then, follow these steps:
Once you have cleared all traces once again and your background is completely white, and the components are countered, you may go to the next stage. In case there are some issues and artifacts, read to the end of this section:
You may paint the background (substrate with any brush tool if you find your accuracy to be appropriate (or if components cannot be deselected properly if they are too complex and small). You should save the selection (the filled substrate) to another level to always be able to edit it.
Eventually, all the components will be replaced with appropriate symbols. But now, you just need to isolate them from the background. You may use rectangle or circle select tools. Perform the complete selection and copy and paste it into a new transparent layer.
It should not be much of a problem as you previously filled the background with black. And now, the selection tool can properly distinguish components themselves.
You should receive something similar to the image below.
Launch Inkscape one more time, and open the .png image of components. Create a new layer, open the tracing made for the solder side, and copper it to that layer. Create a new layer, and copy onto it the picture of holes.
Repeat the same procedure for ground plane holes and circles and free-hole marks. You may also need to add the image of solder layer tracing to confirm the correct arranging of the digital PCB.
After all the detail is done, reorder the layers so the original photo is on the very bottom, then components, the component side tracks, holes, and finally tracking. Use the scaling arrows, so all the images are properly aligned (matches the sizes, angles, and perspectives of each other). Then, perform the following steps:
Use DIa program to open the newly made file. Choose the “Circuit” category of shapes. Then, using the image of components as a guide, snap the replacing symbols over the tracing layer. This way, you will make your work more like a professional engineering schematic.
A quick tip: You may visit the Dia website to download libraries of extra symbols.
You may also attach text to a snape. It’s useful for an indication of connections and components. Add values and identifiers this way as well.
Finally, you should have a vector drawing of all the tracks with added symbols indicating components. Just arrange the components, so they look more like a conventional schematic. Replace lines there they are sloppy. Put additional effort into what seems to need reworking.
Study the power routing throughout the circuit to see if the received schematic makes any sense. Remember, if there are any peculiarities, there is probably a connection hidden from you.
All this doesn’t sound easy enough? Well, it is difficult to claim that such instructions are intended for someone new to the electronics industry. However, if you are an enthusiast having enough experience, you may find the detailed guide to be a good point of start.
You will need a tone of extra research to properly arrange the schematic and perform some of the described steps, depending on the software used and even the operating system of your desktop. Have good luck with reverse engineering a PCB board!
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