How should a resistor value be put on a pcb? - Page 1
Forum section: electronics / beginners

author: alank2
author_rank: Super Contributor
timestamp: February 08, 2021, 03:08:36 am
content: I've been in the habit of just putting the value, like "2K" or "680", but it occurred to me today that this could be confusing if something thinks they are a resistor marking. 680 for example could convey 68 ohms while 681 would convey 680. Any thoughts? Should I put the resistor code and not its value?

author: retiredfeline
author_rank: Frequent Contributor
timestamp: February 08, 2021, 03:30:57 am
content: Never thought that way but you could suffix R as in 680R to remove doubt.

author: ataradov
author_rank: Super Contributor
timestamp: February 08, 2021, 03:51:22 am
content: 680R is the most universal way. But generally you could look at other values around to figure out the convention used. As long as you are consistent, then any style is fine.Also, schematics that use 680 for 68 Ohms are annoying. Especially it gets annoying with capacitors using this style of values.

author: fourfathom
author_rank: Super Contributor
timestamp: February 08, 2021, 04:13:50 am
content: I suggest that you *not* put the value on the PCB silkscreen. Instead, put the component ID# (R17, C3, etc.) and refer to the schematic or parts list for the value. Component values do change on occasion, and there may be details (tolerance, tempco, etc.) that matter. This type of info is important, and doesn't belong on the circuit board.

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2021, 04:17:27 am
content: Having the value printed on the silkscreen is good for beginner targeted kits with chunky through hole components. It makes sense in that application, the parts aren't normally critical enough to matter. With modern surface mount chip resistors there isn't really room on the board, I occasionally struggle to find places for the reference designators. I find it annoying when a board doesn't have those.

author: ataradov
author_rank: Super Contributor
timestamp: February 08, 2021, 04:18:17 am
content: Yes, I've read is as a "schematic" not a literal PCB. On the PCB you should definitely favor designators first and values only if you have space and very judiciously.

author: mvs
author_rank: Frequent Contributor
timestamp: February 08, 2021, 08:25:14 am
content: Quote from: alank2 on February 08, 2021, 03:08:36 amCode might be helpful for assembly, but there are multiple code systems. 10K smd resistor that you order from a supplier can have 103, 1002, 01C or even no print at all.Value is a bit more universal. You can choose style and stay consistent over entire schematic.

author: Ian.M
author_rank: Super Contributor
timestamp: February 08, 2021, 08:43:02 am
content: As others have said, don't bother putting resistor values on the PCB silkscreen. However, assuming you aren't working with 'flysh!t' passives too small to carry any markings, every repair tech who ever works on the board will thank you if you put otherwise unmarked capacitor values on the silkscreen, and for OSHW projects the URL of the repo, or for propitiatory projects, the company name, full model number and board ID.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 08, 2021, 06:04:52 pm
content: Its a headache in SM there's often just no room even for the component ID.

author: wizard69
author_rank: Super Contributor
timestamp: February 08, 2021, 11:37:34 pm
content: I have to strongly disagree with this position. I base this on years of working automation and frankly a PCB should have as much component information as is reasonable to fit on the board. The problem is simply this you may not have access to the schematic nor a parts list.One example here is an old robot controller board that never had a publicly available schematic nor parts list. Some connectors went bad on the board but thankfully the board was silkscreen with a lot of component information. With a bit of googling I was able to chase down the parts, that would have been a lot more difficult if the part information wasn't there.Now with high density boards you will not be able to do this for every part on the board. However it wouldn't hurt to try for things projected to have a failure in the future. So while it can't happen every time or every place on a PCB, when possible it makes sense to label parts with values.Think about it this way, many parts come with the data already printed on them. IC packages, transistors and many other parts get stamped from the factory with their part numbers. If that data is missing (because some idiot painted over or ground the data off), you would get a bit hostile with the manufacture. Sadly with resistors they often obliterate any indication of value when they fail. So it doesn't make sense to say never, rather value labels for something like resistors should be considered on a case by case basis and for some parts should be the norm.Quote from: fourfathom on February 08, 2021, 04:13:50 am

author: wizard69
author_rank: Super Contributor
timestamp: February 08, 2021, 11:47:28 pm
content: Quote from: ataradov on February 08, 2021, 03:51:22 amI hope that designers and engineers take heart to what you have written (highlighted above). Also with modern software and printers I see no reason to avoid non ASCII characters. Ω < see I can do this on the net. Sometimes it seems like what is considered as acceptable is based on the technology of the 1960's.Also you are right about consistency. As someone that works with documentation from manufactures from around the world it can be very frustrating to switch to from one convention to another throughout your day. At the very least as an engineer be consistent with your own products.

author: Bassman59
author_rank: Super Contributor
timestamp: February 09, 2021, 04:51:38 am
content: Quote from: wizard69 on February 08, 2021, 11:47:28 pmI use 68R0 to indicate a 68Ω resistor (1%). The "R" replaces the decimal point, which might not get reproduced correctly. Similarly, a 68.1 k resistor is indicated by 68k1 (1%). Sure, it's an old habit from the days of blueprints and poor photocopies, but it is unambiguous.

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2021, 07:43:51 am
content: I've seen it done like this on the venerable 0-30V 2mA-3A PSU kits. As long as you are consistent. Unfortunately, PCB CADD doesn't support the Greek alphabet, RIP omega

author: wizard69
author_rank: Super Contributor
timestamp: February 09, 2021, 08:28:08 am
content: Quote from: floobydust on February 09, 2021, 07:43:51 amIt is a new century, my question is why? CAD software of all types should easily support any language on earth these days.

author: Gyro
author_rank: Super Contributor
timestamp: February 09, 2021, 09:13:16 am
content: Quote from: floobydust on February 09, 2021, 07:43:51 amUnfortunately they did it at the expense of leaving out the component idents, which are far more important for tying in with the schematic.Component IDs and BOM are the way to go [Edit: assuming that there isn't enough space to put both ident and value on the silkscreen].

author: Kleinstein
author_rank: Super Contributor
timestamp: February 09, 2021, 02:08:14 pm
content: It is rare that one need component values on the silkscreen. It may be handy with very simple kits. But usually the component ID is more important.About the only component that should have a value on the PCB is a fuse.

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2021, 09:21:55 pm
content: Quote from: wizard69 on February 09, 2021, 08:28:08 amI'm not sure what the problem is. Omega is univerally used in electronics and the last time I tried in Altium schematics I ditched the stupid "R" and put in.It all looked good... then when I printed the schematic- it was mangled, no ohms symbolEven on this forum WTFis subscript and corny looking kerning. Sigh.

author: ataradov
author_rank: Super Contributor
timestamp: February 09, 2021, 09:29:00 pm
content: Just write "R". It is far easier to read and it is present in all fonts and on all keyboards if you want to copy or search. Don't make your and other's life harder than it needs to be.

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2021, 09:42:20 pm
content: That's the problem - we've got Unicode, emoji's and yet a few Greek characters defy modern computingEE's should complain more instead of just using R and u.

author: ataradov
author_rank: Super Contributor
timestamp: February 09, 2021, 09:46:55 pm
content: Well, I personally would complain against using weird Greek characters in favor of Latin characters. I don't care how they look, I care how fast I can type. And Latin characters are right here on the keyboard. Greek stuff would require some additional panels or combining key combination - total PITA.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 09, 2021, 09:56:06 pm
content: I put the component ID and values on my boards. It makes assembly a lot quicker. I probably wouldn't do it for a production board but for proof-of-concept it's just one less source of error.

author: Zero999
author_rank: Super Contributor
timestamp: February 10, 2021, 09:23:28 am
content: Quote from: floobydust on February 09, 2021, 09:21:55 pmIt sounds like a problem with the printer driver.QuoteI think it uses the smilie, because the forum used to be limited to ASCII. Now it has unicode support, it should just paste the Latex code or the actual symbol into the text box. It would be handy to have other commonly used symbols such as µ, °, π, ± etc.EDIT:It doesn't use a smilie, for the Ohm sign, but Latex.I don't know why the kerning is off. Interestingly it's betterin the quote, than the orignal posted. When I use the unicode symbol, Ω it's fine though.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: February 10, 2021, 12:43:02 pm
content: Quote from: ataradov on February 08, 2021, 03:51:22 amYou can feel the Soviet roots, when there was no uncertainty in the schemes: the designation without a letter is om or picofarads.At the same time, 6800 was written on the circuit, and 6H8 on the capacitor.It never occurred to anyone to write on a diagram or a board 6H8.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: February 10, 2021, 12:44:31 pm
content: I think using the abbreviations adopted by SMD is not a good tone.On the diagram and on the PCB, it is necessary to use the same designation that is widely accepted, it is the same as our Soviet school, it seems, all over the world.Using the SMD abbreviations on diagram or PCB is like drawing a circuit in the form of part housings and wires, as the arduino followers do, for example.I would not do this for children's crafts, it is necessary to teach from childhood to intelligent activities, and not to be monkeys.

author: tooki
author_rank: Super Contributor
timestamp: February 10, 2021, 10:53:13 pm
content: Quote from: floobydust on February 09, 2021, 09:21:55 pmI have used lots of Ω (there's the Unicode, not the embedded LaTeX the omega smiley inserts) in Altium, and it works fine — but I always set the font to Segoe UI (the system font in Windows Vista and later). Looks good on screen, prints nicely, works well for silkscreen, and has a comprehensive character set.

author: tooki
author_rank: Super Contributor
timestamp: February 10, 2021, 10:56:15 pm
content: Quote from: Zero999 on February 10, 2021, 09:23:28 amThe embedded LaTeX gets rendered to a bitmap image, which is then just inserted inline, hence the wonky spacing. (It's not kerning, by the way — that wordspecifically/exclusivelymeans the manually tweaked horizontal spacing between specific letter pairs. Manually in the sense that the font developer embedded manually tweaked kerning tables into the font.)