hand drawing the schematic of a PCB - Page 1
Forum section: electronics / beginners

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: May 06, 2015, 07:08:04 am
content: A small part of my first job in the 1970s was to lay out PCBs from drawn schematics (sometimes my own drawings). I enjoyed doing this and was quite competent at it.I read schematics of all complexities on a daily basis.For the last few decades I have drawn out schematics from PCBs mainly for hobby repairs of a great variety of equipment- from audio amps, ignition systems, motor controllers etc etc you name it...I realised today that I am not very good at it, and struggle to make a decent tidy, logical drawing of quite simple circuits. Quite frankly it takes me ages !I would appreciate any comments, tips or general observations on this problem.Regards, BT

author: tggzzz
author_rank: Super Contributor
timestamp: May 06, 2015, 08:23:01 am
content: Quote from: BurningTantalum on May 06, 2015, 07:08:04 amTidyness is easily solvable by using any of the free schematic/layout programs available, e.g. DesignSparkPCB, Eagle, KiCad, etc"Logical" implies understanding of what the circuit is supposed to do and how it is supposed to work. A key concept is standard "design patterns" are drawn in standard ways, e.g. current mirrors and opamp integrators each have their own canonical schematics. There's no short cut to getting that right.Since I'm European, I prefer signals to enter on the left/top and leave on the bottom/right. Apparently many others (non-European first language?) don't bother.

author: mikerj
author_rank: Super Contributor
timestamp: May 06, 2015, 11:03:18 am
content: Working backwards from a PCB to a neatly drawn schematic is extremely difficult to do in one pass unless it's a very simple circuit or you already have a very good idea what the circuit looks like. If I'm doing this I don't worry too much about neatness on the first schematic, just get it electrically correct and then re-draw it neatly.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: May 07, 2015, 02:30:53 am
content: Thanks both.I too can only draw from left to right - in to out.I posted because I ended up a bit frustrated yesterday, after creating a big heap of torn off notepad pages and still not making a very good job of drawing a relatively simple circuit that I was repairing. Having said that- I recently managed to draw a fairly complicated (because of the number of multi winding inductors/transformers) industrial ultrasonic transducer driver PCB. I did this by taking a photo of the track side and processing it to black and white, then printing it and drawing in the components. It seemed easier then than constantly turning the board over by hand, and it was quite heavy with chokes and ali heatsink. I then drew the circuit in a standard layout.I have never done a netlist first, so will maybe try that as it will at least be a check of the connections in the drawing.I have had a cursory play with TinyCAD and LTSpice etc but I seldom need a PCB layout. I wasn't aware that any CAD program was available that will draw a schematic from a netlist.Thanks, BT

author: suicidaleggroll
author_rank: Super Contributor
timestamp: May 07, 2015, 02:56:19 am
content: This isn't something I do often, so I was wondering if there's a reason people don't use the normal schematic -> netlist -> layout process in reverse for reverse engineering a PCB?By that I mean:1) Make schematic symbols for the ICs in pin-order2) Place those symbols on the schematic sheet in their installed locations on the PCB3) Connect the pins as they are on the PCB4) Generate the netlist5) Make device footprints with logical, rather than physical pinouts (like you'd normally do with a schematic symbol of the device)6) Layout the "PCB" in a traditional schematic fashion, with inputs on the left, outputs on the right, etc.

author: charlespax
author_rank: Regular Contributor
timestamp: May 10, 2015, 03:16:07 pm
content: I generally break out logical sections into their own area as you can see in the attached image. This allows me to easily move things around as I need to add more parts. For example, if I need to add a few parts to the temperature sensor section, I can easily select and move the other sections to make some space.In Eagle and other programs you can even break the schematic into pages. I wouldn't date make one giant schematic. I've burned myself on that before