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Following this poll, the EE.SE community has determined that component identification questions should be allowed, though we need some better guidelines. This post contains guidelines on how to ask a good component identification question, and what to do when they're not good.

In general, most people will only look at a component identification question once, so make sure you have all the information in place before you post your question.

Rules for Asking:

  • Include a clear picture of the part in question, including a ruler if possible for scale.
  • Type out any text on the part. Many parts have text that is difficult to read from a picture.
  • Include any information about the surrounding circuit, or any knowledge on the type of system your component came from.
  • Include the tag.

What helps:

  • Make sure the picture of your component is clear, focused, and has something to compare dimensions with (e.g. a ruler)
  • Add a second image that shows where the component is located in the board/system
  • Show a schematic if you have it, or a tracing of the PCB traces if possible.
  • If you know what the package is, or what the specific dimensions are, that can also help (e.g. a 24-pin SOIC)

Ground Rules:

  • Only one component per question. Questions with more than 1 component will probably be closed as "Too Broad"
  • "Components" includes connectors, batteries, battery cells and packs, single active devices, passive devices or networks, integrated circuits, and other parts that an EE would use in a design or prototype.
  • "Components" does not include: printed circuit boards (bare PCBs), whole circuit boards with components installed (PCB assemblies), parts that fall in another domain (wall outlets or spark plugs), or lawn mowers.
  • Parts that were intentionally obfuscated (e.g. the board manufacturer sanded off the part number) will not be considered. This also includes chip-on-board with an opaque epoxy.
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    \$\begingroup\$ If you have something you would like to change or add, post an answer below so the community can vote on it. \$\endgroup\$ – W5VO Sep 9 '18 at 23:37
  • \$\begingroup\$ Coming back to the recent controversial identification question: does an unlabelled battery pack count as obfuscated? What about unlabelled chokes/transformers and similar custom components? \$\endgroup\$ – Dmitry Grigoryev Sep 10 '18 at 12:31
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    \$\begingroup\$ "obfuscated" does not equal "unlabeled" \$\endgroup\$ – Scott Seidman Sep 10 '18 at 12:52
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    \$\begingroup\$ @ScottSeidman I think intentionally obfuscated captures the intent. It's really to protect against a black box with the identifying markings removed. Connectors, another popular identification target, usually have no markings on them at all. \$\endgroup\$ – W5VO Sep 10 '18 at 13:33
  • \$\begingroup\$ right. I think unlabelled items often come up in this category, and it's usually fine, especially for connectors. \$\endgroup\$ – Scott Seidman Sep 10 '18 at 13:48
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    \$\begingroup\$ Not just that, but a "we cannot determine it because of x y z, but its likely to be a this type of part" answer can be posted. No reason to have that last bullet point at all. \$\endgroup\$ – Passerby Sep 10 '18 at 17:22
  • \$\begingroup\$ For those that don't understand how to look for parts there is a question here (disclaimer I wrote it): electronics.stackexchange.com/questions/334128/… \$\endgroup\$ – laptop2d Sep 12 '18 at 22:51
  • \$\begingroup\$ Once we've chewed this through meta long enough, we should copy/paste the above text as whole and put it in the identification tag wiki. \$\endgroup\$ – Lundin Sep 20 '18 at 13:20
  • \$\begingroup\$ Perhaps we should expand the guidelines a bit, to include the package of the component, if it's known. \$\endgroup\$ – AndrejaKo Sep 27 '18 at 6:38
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I think these guidelines generally make sense. However, this part needs some adjustment:

Parts that were obfuscated (e.g. the board manufacturer sanded off the part number) will not be considered. This also includes chip-on-board with an opaque epoxy, and parts that are burned beyond recognition.

We've had some legitimate questions where a part was burned beyond recognition, and the OP was trying to figure out what it might have been. Obviously just a picture is not good enough then, but this can be a good question if the schematic is shown, and we understand what the unit as a whole is intended to do.

A picture might show a blown diode was in SMA package, and from the schematic we can see that it is a rectifier that needs to handle 30 V in reverse, and carry under 1 A. That's enough information to know what to replace the blow part with.

Conversely, the picture could be the same, but the schematic shows a zener diode used as a 5.6 V source. Again, good and useful answers can be written.

These example do run the risk of being repair questions. The distinction is between "What do I replace this part with?", and "How do I use this information to infer the part specs?". That distinction won't be obvious to everyone, but that doesn't mean good questions of this type can't be asked.

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  • \$\begingroup\$ To your first point, would a change to "intentionally obfuscated" help? \$\endgroup\$ – Scott Seidman Sep 10 '18 at 13:20
  • \$\begingroup\$ @Scott: That would help. Leaving off mention of parts being unrecognizable due to failure would help too. \$\endgroup\$ – Olin Lathrop Sep 10 '18 at 13:28
  • \$\begingroup\$ My thoughts were that if the top of the package was blown off, it's unlikely that we will be able to identify the part number. There's a few questions that come through where someone has opened up their microwave and found a burned part and asked what it is to replace it. \$\endgroup\$ – W5VO Sep 10 '18 at 13:31
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    \$\begingroup\$ It might be unrecognizable with respect to part number, but recognizable enough to narrow it down to a general type of component, which is educational in and of itself. For example, "this is most likely a bridge rectifier, as the circuit section you point to converts an AC mains voltage to a DC supply for your board. Typically, this involves.... \$\endgroup\$ – Scott Seidman Sep 10 '18 at 13:37
  • \$\begingroup\$ Exactly, these questions, and circuit design in general, do not need to be 100% accurate to the part number. You can replace a given part with an equivalent part easily. \$\endgroup\$ – Passerby Sep 10 '18 at 17:00
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One thing that I think should be a requirement:

The question title should be a short description of the component

Instead of What is this component? the title should be What is this blue plastic cylinder with two wires?.

The former is very annoying on the front page, because every identification question looks the same so it is difficult to remember if you have seen it before.

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Regarding "Type out any text on the part.":

It would perhaps be useful to remind OP to actually search for the text themselves before posting, noting that the downvote button popup includes the text This question does not show any research effort.

If the result is confusing, at least mention this in the question. Cutting off just the right part of the IC markings to get a good result is something of an art, but mostly It Just Works™.

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    \$\begingroup\$ My experience with googling the marking of a chip (if it isn't a microcontroller) is that you almost never get a direct hit without some of the art you mention. So I'm not sure if this requirement would actually help to improve the question. \$\endgroup\$ – Arsenal Sep 11 '18 at 6:56
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    \$\begingroup\$ Other complications are knowing the manufacturer logos by sight, marking "codes" on small packages that aren't the actual part number, and figuring out what might be date codes/lot codes. \$\endgroup\$ – W5VO Sep 11 '18 at 18:31
  • \$\begingroup\$ This goes for any question, not just identification ones. \$\endgroup\$ – Lundin Sep 20 '18 at 13:15
  • \$\begingroup\$ @W5VO mentioning manufacturer logos makes me wonder, do we have a canonical "what is this logo" question on here, and if not, should we? It seems like a community wiki with logos (as marked on parts) of common IC makers might be a good thing to have. \$\endgroup\$ – Hearth Oct 6 '18 at 17:02
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Another thing that really helps is:

  • If they know something about the voltages on any of the pins around the part, ie which pins are ground or Vcc.
  • Probe the part with a meter, especially if it could be a transistor or a diode with a meter in diode mode
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  • \$\begingroup\$ Can't imagine why this is getting down voted. Asking "what is this thing" without taking some measurements is the same to me as a homework question with no attempted answer. I'd think this should at least be under the "What helps" note, if not a flat out requirement. \$\endgroup\$ – Phil C Sep 14 '18 at 1:26
  • \$\begingroup\$ @PhilC This can't be a requirement because some of the questions asks for broken components or components in isolation. What are you going to measure on an unknown 16-pin IC or a mystery 4-pin black box? \$\endgroup\$ – pipe Sep 15 '18 at 22:24
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    \$\begingroup\$ On unknown chips you can deduce vcc and gnd, you can do this even with isolated components. If you have other components which have known pins, you can find vcc and gnd, then ohm out which planes they are connected to to find what the unknown parts are. I have reverse engineered products in this manner \$\endgroup\$ – laptop2d Sep 15 '18 at 23:59
  • \$\begingroup\$ @pipe Doing a ohm and diode test on a 4 pin black box can tell you pretty quickly if it's probably a rectifier or relay. As laptop2d said, you can test the circuit even if the part is cooked. The location, or absence, of vcc and gnd can help narrow the field. Especially if you find a negative supply voltage. Then there are these questions that could have been avoided completely if a basic resistance test was done. Seems to me that a demonstration of the bare minimum first steps of troubleshooting shouldn't be too much to ask. \$\endgroup\$ – Phil C Sep 16 '18 at 0:57
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    \$\begingroup\$ Yeah, this is more of a what helps thing \$\endgroup\$ – laptop2d Sep 16 '18 at 1:42
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I recommend making the photography instructions contain more specific guidance, since many people don't have experience with taking good technical photos. I would say:

  • Well lit. Details should be crisp, not noisy from lack of light. There should be no overexposure (white blobs) hiding colors and details. (Using a basic photo editor to improve contrast afterward may be worthwhile, too, but it can't improve what wasn't there to start with.)
  • In focus. Edges should be sharp. After you take the picture, zoom in on it to check; don't just judge it from the tiny phone/camera screen. A camera mount or leaning your elbows on the table while you take the picture can help, as will providing good lighting.
  • Cropped so as to show the component at a reasonable size when displayed in the question. Consider including an original or second photo with an overview of the board or other surrounding components. Avoid painting a thick box around a component on a board as this may hide relevant information of how it is wired up.
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