Is there a way to wire the lighting on an illuminated switch so that it's powered by a separate dedicated battery and NOT by the matrix encoder device that the switch is a part of?

I have a USB matrix encoder that only provides +5V, and all the common illuminated switches seem to require 12V, give or take. I think this would basically mean having two isolated, separate circuits, where the intersecting factor is some one (latching) switch. Is this possible?

Another alternative that I could go for is, picking a regular non-illuminated switch but having it control an externally powered indicator LED that makes up for the actual switch's lack of internal illumination.


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    \$\begingroup\$ Based on your comments it seems like your difficulty arrises from wanting to deal with discount vendors who won't provide data sheets - that's not really engineering design within the mission of this site, but effectively has the issues of an end-user question. For design purposes you should pick something with a data sheet, or pick something you believe is likely enough a clone or equivalent of something that has one that you're willing to risk the time and expense of buying and evaluating it. Try picking out documented parts that meet your needs and then look for something like them. \$\endgroup\$ – Chris Stratton Jan 6 at 20:23
  • \$\begingroup\$ @ChrisStratton please see my comments on the next answer on vendors; Where I am, there actually isn't a whole lot of alternatives, and online, it's not too easy to find a vendor who has all: international shipping, no minimum order, and a lot of alternatives on same type of product, with a lot of precise info. Suggestions are very welcome, as long as they're not US-centric as the default tends to be. \$\endgroup\$ – user158589 Jan 6 at 23:40
  • \$\begingroup\$ You seem to have misunderstood the above. Identifying vendors you can work with or even specific parts to try to buy from anywhere is off topic here. Looking at online catalogs of vendors you cannot work with is still beneficial to you, because it can help you figure out the type of part you are trying to source from a place you can work with. \$\endgroup\$ – Chris Stratton Jan 6 at 23:46
  • \$\begingroup\$ @ChrisStratton But indeed mainly this question isn't about where to get parts, it's about 1) is this isolation possible, and 2) what kind of wiring it is. I just don't have enough experience to spontaneously engineer this solution, which is why I ask. If there exists a common term for the solution that I seem to be looking for, I'm happy to do further reading independently. But whenever a problem consists of extremely common elements and what makes the problem specific is found between the lines, it's really hard to find info merely by searching by the keywords which appear too frequently. \$\endgroup\$ – user158589 Jan 6 at 23:47
  • \$\begingroup\$ @ChrisStratton Oh okay. Makes sense. Especially if I can identify different vendors selling the same product, I can get valuable info from one, even if the other one was the one I purchase from. \$\endgroup\$ – user158589 Jan 6 at 23:49

Typically a built in illumination source in a switch would be electrically isolated (at least for moderate voltage differences) from the switch contacts to give the designer maximum flexibility, but of course you would have to read the data sheet of any particular part to verify that is the case.

You are quite likely mistaking the switch contact maximum voltage rating for the illumination source operating voltage. Most modern illuminated buttons for low voltage circuitry will have an LED. The online catalog I am looking at shows both the rated contact voltage, and the LED forward voltage, where the latter is usually in the range of 2-3 volts or so. Such a keyswitch could be used in a 5v system with an appropriate current limiting resistor in series with the LED.

It is of course possible that there are illuminated button switches already including a series resistor appropriate to 12v supply; on 5v these would draw much less current than intentended and be fairly dim, so you probably want to avoid those. And of course types of illumination other than an LED are possible, too. For example something intended for mains might use a neon bulb with a resistor, or have a dropping circuit to use an LED.

  • \$\begingroup\$ Yeah, it seems that data sheets are only sometimes available: Many switches are "non-brand", and out of the most interesting looking ones I find, they are often vintage, thus they're pre-internet, no info of them online. \$\endgroup\$ – user158589 Jan 6 at 20:08
  • \$\begingroup\$ A lot of the illuminated 12V ones seem to be "advertised" as something for cars or boats. I'm just having a hard time spotting anything that would be especially designed for low voltage use. It's due to my inexperience that I can't recognize when it's okay to use a product that doesn't boldly state that it's exactly for my intended purpose only. I basically have to shop online in places that ship internationally with no minimum order requirements and don't charge the same industrial scale shipping costs when all you want is a couple of components. This also limits the platforms where I > \$\endgroup\$ – user158589 Jan 6 at 20:14
  • \$\begingroup\$ ... search for components, and these certain platforms are nightmarish at filtering and searching by very specific features, unlike massive industrial warehouses that sell stuff to businesses and industries in massive bulks. \$\endgroup\$ – user158589 Jan 6 at 20:16
  • \$\begingroup\$ Yes, I have been under the impression that the markings are for maximum ratings. I don't care about them when I choose normal switches, but in terms of illumination, I've thought that too much power either won't light up the LED or it's very dim. 5V and 12V are quite far apart so I'm guessing that it is significant in terms of brightness. I don't know what is the actual minimum voltage for a LED to light up at all. And if it matters: my matrix is already prepared with signal diodes for every single switch point, to prevent ghosting. \$\endgroup\$ – user158589 Jan 7 at 9:57

You need a swithch with isolated ilumination terminals or if you want to use the switch with a matrix.

This form of switch is more common in the PCB-mount key(board) switch form-factor than in the panel-mount button form. In the key-switch button it's usually just a bare LED with no resistor so it can be adapted to any convenient voltage.

Another option is to use the switch with a parallel interface (like an arcade joystick interface instead of using it with a matrix) then you can use a switch with non-isolated illumination.

  • \$\begingroup\$ The matrix is currently a must: I have a specific connector coming from the main encoder that distributes the matrix in a bit of a star topology manner because multiple full or partial copies of the same matrix are to be distributed as multiple end devices. The illumination can not be "seen" by the actual matrix, the matrix should only see the switch. I think. \$\endgroup\$ – user158589 Jan 6 at 20:03
  • \$\begingroup\$ Isolated illumination terminals: how many pins are we talking about, for such switch? A bare LED would be perfect in the sense that I would know what's happening and it would be a matter of reading some articles, to find out what I should do with the whole resistor business. But the internally illuminated ones almost solely seem to be for cars and such. So, always a 12V mark and no way of disassembling the part. \$\endgroup\$ – user158589 Jan 6 at 20:03

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