Help doing a reverse engineering of a circuit board  - Page 1
Forum section: electronics / projects

author: Shaydzmi
author_rank: Regular Contributor
timestamp: May 28, 2020, 08:27:02 am
content: Hi,Can anyone help me reverse engineering this circuit board?Thank you.

author: Dubbie
author_rank: Unknown
timestamp: May 28, 2020, 08:33:01 am
content: I have found it helpful in the past to take high-quality photos of both sides and overlay them precisely in photoshop or some other image editor. That way you can see how each component connects to the next without flipping back and forth and trying to figure out which solder joint is which. This is not a must, just a nice-to-haveOnce you have done this, you can begin sketching the circuit. You will probably have to redraw it a few times as you realise what each block is, and how it should "properly" be drawn. As you go, you can identify each component and try to read it's value. Failing that, remove the component and measure it. There may be some damaged components, and for those, you'll have to wait till you know what the circuit does so that you can make an educated guess at a replacement.

author: Berni
author_rank: Super Contributor
timestamp: May 28, 2020, 10:28:25 am
content: As Dubbie said, you need a good overlay photo that shows both components and traces.But since this is single sided it might be enough just to put a light behind the board so that the traces cast a shadow trough the PCB. Then as you draw a schematic just color the traces on your photo so that you know what traces you already reverse engineered (Either do it digitally on a computer or print it out and color over the photo with a highlighter pen)

author: Shaydzmi
author_rank: Regular Contributor
timestamp: May 28, 2020, 10:35:56 am
content: Thank you,Can't you do it for me just from the photos?

author: Berni
author_rank: Super Contributor
timestamp: May 28, 2020, 11:13:26 am
content: Quote from: Shaydzmi on May 28, 2020, 10:35:56 amFirst of all you can't see all the comonent markings on the photo to know what they are, they might be BJTs, maybe FETs, mabe ICs, maybe diodes, maybe triacs...etcIts boring work that takes a while, so i don't think anyone would want to do it for nothing. You can see where the traces go, so just draw it all onto a piece of paper. Google up all the parts to find what they are etc... you can do the boring grunt work.Where you might benefit from asking on forums is for help understanding what each part does. Since you might get a tangled mess on paper and are having trouble organizing it in a good way.And if you don't have enough knowledge to get this far, then you probably would not have much use for the reverse engineered schematic that comes out as a result, apart from perhaps cloning a product (And in that case you have the budget to pay someone to do the work)

author: Gyro
author_rank: Super Contributor
timestamp: May 28, 2020, 11:33:01 am
content: [EDIT: Yes (sorry Berni)] Holding the board up to a reasonably strong light (and preferably photographing it) is another useful way of seeing the traces from the component side of the board.Obviously you can't see the traces underneath the components but it helps. Example:

author: Shaydzmi
author_rank: Regular Contributor
timestamp: May 28, 2020, 11:42:31 am
content: Quote from: Berni on May 28, 2020, 11:13:26 amYour opinion is respected, but if I followed such advice before, I couldn't learn anything throughout my life, I learn something new every day.

author: Berni
author_rank: Super Contributor
timestamp: May 28, 2020, 12:09:14 pm
content: Quote from: Shaydzmi on May 28, 2020, 11:42:31 amYou will learn even less if someone does the whole thing for you and hands you a final cleaned up schematic.There is plenty to learn trough the process of reverse engineering. The first part of drawing it onto paper actually required no knowledge at all, just following lines. Any kid that can solve a maze can do that, you don't even need to know what the components are.Its the other steps that actually require knowledge of electronics, like recognizing the components in order to turn them into appropriate symbols, for something like a resistor its easy, but for semiconductors you need to google partnumbers. Being able to google info about a component is also a basic electronics skill that almost all electronics enthusiasts can do. Its the last part of redrawing the schematic into a neat logical layout that needs the most skill since it usually means you have to understand how the circuit works.The way you learn this is just to go at it on your own and ask questions on forums like this for points where you get stuck. So instead of asking "Can anyone turn this photo of a board into a schematic" you ask things like "What is this 3 pin component in the photo?" "How do i read the resistor value on this resistor?"..etc and once you do have the board turned into a messy nonsensible schematic that needs ordering you might ask "Can someone explain this confusing part of the circuit and maybe clean it up for me?". That way by the end of it you will have learned not only what the board does but also how reverse engineering is done so that you can do it on your own next time.Give a man a fish and he won't be hungry for a day, but teach a man how to catch fish and he won't be hungry for the rest of his life

author: Shaydzmi
author_rank: Regular Contributor
timestamp: May 28, 2020, 02:06:38 pm
content: Thank you very much, now I agree with you, I'll try what you said.

author: Shaydzmi
author_rank: Regular Contributor
timestamp: June 02, 2020, 07:00:17 am
content: I've done this:What is the next step?

author: Renate
author_rank: Super Contributor
timestamp: June 02, 2020, 12:54:00 pm
content: Huh? I already gave you the guts of this on the other thread.https://www.eevblog.com/forum/projects/need-some-help-building-a-circuit-involving-switchs-and-relays/msg3083532/#msg3083532All the rest of it is transistor drivers for the relays, something you can just invent yourself.

author: Berni
author_rank: Super Contributor
timestamp: June 02, 2020, 12:58:02 pm
content: That is a good first step.Now comes the more skillful step of arranging the components into a sensible layout.First step in doing this is usually finding the ground and power supply lines. Those usually connect to most parts of the circuit and you know what the purpose of those is, so it solves a lot of nodes in the circuit. You might want to draw the ground traces in black on your diagram. Then you start redrawing it. Typicaly replace ground and power connections with ground symbols to make it clearer and move it around into what seams sensible configurations.

author: Shaydzmi
author_rank: Regular Contributor
timestamp: June 02, 2020, 01:19:56 pm
content: Quote from: Renate on June 02, 2020, 12:54:00 pmThank you, I didn't understand what you did, so I decided to go step by step myself, to understand this circuit.Now I want to simulate this circuit.

author: Shaydzmi
author_rank: Regular Contributor
timestamp: June 02, 2020, 01:23:48 pm
content: Quote from: Berni on June 02, 2020, 12:58:02 pmThank you, I'll do what you said.