Hello,
This is my first post, and I am a total newbie at this…
I have a Scorbot ER3 robot with a misbehaving encoder. A schematic is not available, so decided that I decided to reverse engineer and make a schematic.
The very first chip that I need to map the pins is a 74LS14N Schmitt-Trigger Inverter that looks like this:
So… Here are my newbie questions:
If I create my own custom symbol by changing the graphic style from inverted to line (and faking a invertor circle in the graphic) will this screw something up further downstream? I have know idea how far I’m going to go with this, but I just as soon do it correctly from the get go.
I’m assuming its not that hard to convert a Ecad format to Kicad? I googled and it seems like there is stuff out there? What’s the recommended easiest way to convert? Any drag an drop website convertors out there?
I spent a fair amount of time googling looking for Kicad symbol for a 74LS14N and came up dry. Am I just not looking in the correct spot??
Thanks in advance a looking forward to your response.
(After I hit create topic, I discover I can only post one image… So hopefully this still makes sense
JT
I am at the computer with only my libraries. I’m sure when you install KiCad with all its libraries you should find there a right symbol for 74xx14 element. The right symbol for schematic will not look like the picture you showed. Schematic task is to make it clear how the circuit works and not where each inverter (gate) is located in their common case. So the symbol will be of only one inverter. Than at schematic they will typically get references telling which part in IC was used for each inverter so they will got names like U1A, U1B,…
If you wont to copy the information from PCB you can do it using just pen and paper to have the IC looking like real part looks and then when you have there all connections rewrite it to schematic in KiCad.
Request for a “cool looking” inverter symbol is … unusual.
I can not think of a reason why using normal output pins instead of inverted pins would get you into trouble, so you can just use a normal output pin and set it’s “graphic stye” to normal. If you also set the “pin length” to 0 then the pin collapses into only the attachment point dot and you have even more freedom in what you want to draw.
A very important tip is to always keep the attachment points of the pins on a 50mil grid. For any other graphics of schematic symbols you can use any grid you like, but the attachments points must be on a 50mil grid or you will get into big trouble later.
Thanks for the response… This was along the lines of what one of my makerspace buddies was saying. I am way overthinking this… I can easily copy/paste the rough layout that makes sense to me and make a hard copy to write on. I just had it in my head to go directly to the computer without the interim step of writing it down first. The more I think about it the more your suggestion makes sense.
I was going post a picture of the board I’m trying to reverse engineer. I was just looking at your community guidelines about “Post Only Your Own Stuff”. The board I’m reverse engineering was copyrighted in the 80’s… My understanding copyright in this instance only is good for 10 years. Is it ok to post pictures of this board on this forum if I have technical questions?
And yes I was getting warning messages about the attachment points.
I was surprised that there was no automatic move and snap to grid feature.
As I said, I’m trying to reverse engineer a board and this is my first time using this type of software.
I’ve been told I have an unusual way of looking at things.
I’m also interested in hobby versions of industrial robot arms, and I forgot which one the scorbot AR3 was so I looked it up.
The user manual is not hard to find, and as I was curious what other people do with it, I did a search on github, and there are over 50 repositories on github for the scorbot (variants) https://github.com/search?q=scorbot&type=Repositories From simple arduino like things to connection with ROS.
About the reverse-engineering thing. A common way for this is to make a scan of both sides of the board in a flatbed scanner, post process the pictures into B/W and then use KiCad’s bitmap to component funktion to get it into Pcbnew, where you can use it to draw “real” tracks over it, and place the components imported from the schematic. It’s described in more detail here:
It looks like you’re trying to create a schematic that mirrors the physical board in layout as well as function. Since you’re a newbie, let me suggest a different approach.
A schematic is intended to describe the functionality of a circuit, not its physical layout. Matching the physical layout will result in a confusing nest of criss-crossing nets that is hard to follow. That’s why multi-part components like the 7414 hex inverter don’t have a symbol that looks like the physical packaging. Instead, the library provides a symbol representing a single inverter that can be added to a circuit wherever it makes the most sense from a functional point of view. This makes it much easier to understand the operation of a circuit.
It’s only when you get to laying out a board that you start to care which of the six inverters in a package you’re going to use. When routing nets a designer might find that the original choice of which inverter is used causes routing difficulties that would be solved by swapping, say, inverter 1 with inverter 5 in the same package, or between inverters in different packages.
Take a look at any modern schematic and you’ll see what I mean.
I have a couple of objectives here. One is motor #2 is not functioning properly. I suspect it’s an issue with the encoders (Pins 1 and 21 on the main connector)
I want to fix this, but also understand how it works. So this is what I’ve been using to reverse engineer…
So far no kicad, just Pinta and Inkscape.
In your shoes I would just use pencil and paper to work out the schematic, not trying to connect lines to packages but just label the gates used, e.g. U16A, etc. Trying to replicate the physical layout interferes with re-creating a logical schematic where the placement isn’t relevant. For the 3 to 8 decoders, of course those are single units. After you manually drawn a schematic and it makes sense, you could make a neat version using eeschema.
This is how “Big Clive” does the reverse engineering.
He prints out photographs of the top and a mirror image of the bottom of a PCB, and puts them next to each other.
