Schematics: How to use the grid reference and...  - Page 1
Forum section: electronics / beginners

author: HecticZA
author_rank: Contributor
timestamp: April 12, 2018, 08:44:37 am
content: Good day.Not sure if this is the correct terminology, but how do I use the grid references on the side and bottom of each schematic page?I assume it is to quickly find the location on a pcb?I can't find the same reference on motherboards though? If I call correctly they are normally from A - E and 1 - 5?Second question.Looking at a schematic, is there a way on to determine on which side of the circuit the component is located, ie Top or Bottom?This goes for PDF and boardview files.Sent from my SM-N950F using Tapatalk

author: MarkF
author_rank: Super Contributor
timestamp: April 12, 2018, 09:21:01 am
content: If I understand your question correctly--For signals that come from/go to another page of a schematic, the signal name, page number and grid reference are usually labeled. The grid reference being the location on the other page to facilitate finding that signal. Similar to giving a reference on a road map.

author: HecticZA
author_rank: Contributor
timestamp: April 12, 2018, 09:31:26 am
content: I'm referring to the side and the bottom Mark.On the motherboard schematics, there are normally block grids labeled A, B, C, D and I think E. That is from top to bottom. And at the bottom it would be 1, 2 3, 4 and I think 5.That would be from left to right.So a component would maybe in Grid C4 on the schematic.I'm not sure how to use that info to locate the component quickly on the motherboard.It is not a huge problem, as the motherboards are not that big, but was just wondering about it.Same for the bottom or top side. Is there an indicator to show if the component is placed on the top or bottom side?Sent from my SM-N950F using Tapatalk

author: jpanhalt
author_rank: Super Contributor
timestamp: April 12, 2018, 10:20:16 am
content: It might help if you told us what program you were using. I use EAGLE and there is no "top" or "bottom" side to the schematic (older limited version).Keeping to the grid, whether it displays or not, is useful to ensure everything that looks like it is connected is connected.

author: dmills
author_rank: Super Contributor
timestamp: April 12, 2018, 10:39:54 am
content: Assuming you are talking about the stuff around the edges of the schematic sheets, it generally bears no relationship to locations on the PCB.Where it is useful is that it makes it possible to have automated test gear print something like "U47, Page 4, location C3 is not responding", which is helpful when trying to repair some bit of industrial kit.Old HP test gear was sometimes spectacular for this:"PLL Lock failed : 60% A11 Reference board, 25% A10 DIF Counter, 10% Power supplies."And they had this sort of thing for all the self tests, expensive and time consuming to create, but utterly wonderful.Regards, Dan.

author: HecticZA
author_rank: Contributor
timestamp: April 12, 2018, 01:22:19 pm
content: Quote from: jpanhalt on April 12, 2018, 10:20:16 amI'm referring to schematics that are downloaded, normally as a pdf. So basically any PDF reader. The Boardview files obviously use other extensions, but don't think they have those grids.Quote from: dmills on April 12, 2018, 10:39:54 amYes, it is the outer frame / edge.Will add an screenshot.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 12, 2018, 02:00:43 pm
content: Quote from: HecticZA on April 12, 2018, 01:22:19 pmIf you are designing a board based on a downloaded PDF schematic, what goes on top or bottom is entirely up to you within reason. However, I would not recommend that approach. I recommend building a schematic to match the downloaded version using your favorite program that allows schematic capture. There may be errors in the schematic or ambiguous connections. Going through that process yourself will help detect those errors. And, depending how good you are with mirror images, having schematic capture will facilitate making correct connections to those components you decide to put on the bottom.Probably the only times I haven't done that is when bread boarding a very simple schematic on a solderless breadboard or using a manufacturer's recommended design on a breadboard of either solderable or solderless type. Once I get to a PCB, I cannot recall a single instance in the past 25 years when I did not have a schematic first and rely on schematic capture.

author: ebastler
author_rank: Super Contributor
timestamp: April 12, 2018, 06:23:39 pm
content: @jpanhalt: You are misunderstanding the OP. When he talks about "top" and "bottom", he means the upper and lower edge of the sheet of paper that holds the printed schematics. And he is asking about the coordinate grid (letters/digits to designate rows and columns) that is printed there.@HecticZA: You can use these coordinates e.g. in technical documentation that refers to the schematic, to make a component or signal easier to find. I dont recall seeing signal references labelled that way, as MarkF described in the first reply; but I can see that it might be helpful to find signals in large schematics.For smaller designs, you might as well ignore the references entirely. Most PCB CAD programs probably have templates for the printed frames which do not show the references.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 12, 2018, 07:34:53 pm
content: Quote from: ebastler on April 12, 2018, 06:23:39 pmOP said:QuoteFirst, I interpreted "Second question" to mean it was separate from the first question, and in combination with "Boardview," I assumed that meant top and bottom of the board, which of course could mean front or back faces versus top edge and bottom edge.On re-reading it and based on the consensus of the responses, I agree, the OP is probably referring to the top edge and bottom edge. Thanks for clearing that up.However, my answer remains much the same. Position on a schematic is largely irrelevant to the board, and I would still redraw the schematic for anything even of that relatively simple complexity (post #6) if I were making an etched board for it.

author: rstofer
author_rank: Super Contributor
timestamp: April 14, 2018, 04:23:30 pm
content: The grid has no relationship to the board layout. It is simply there as a reference for any "Theory of Operation" documentation that might want provide a quick reference to the schematic. Or any other documentation, for that matter.If you use something like ExpressPCB software, you will have the grid references and they are still useless. What is nice is that the schematic is linked to the PCB layout so you can chase signals around the PCB. This is true on other software but I have never used anything else so I can't say anything about those programs.