Permanent USB connection inside an enclosure

[jmaja]

I'm designing a PCB, which will be installed inside an aluminum enclosure and needs to be IP67. It has a permanently connected USB cable. In the previous model I used a FTDI module, which had a mini USB B and thus the cable needed to have a mini USB A end. The problem was it won't fit through a reasonable size cable gland without tapering the plastic off the connector (not necessary to remove the actual metal connector with M12 cable gland). Only 12 Mbs is needed.

Now I will use a FTDI chip on PCB thus I can freely choose how to connect the USB cable. What would be the best option? It would be nice, if the user could replace the USB cable when damaged. The PCB will be hand soldered.

Would a screw terminal block work just fine? Or is it better continue using USB mini?

For using mini I'm wondering how freely can I choose how far from the PCB edge the connector is placed. I would probably use the THT version. Some datasheets give 2 mm extension outside the PCB edge and some don't even show where the PCB edge should be. It would actually help if the connector would be totally on top of the PCB. Is there any other limitation to that except that at some point the USB mini A plug plastic will hit the PCB edge?

[AndyC_772]

For a permanent connection inside an enclosure I wouldn't choose a mini or micro USB connector. They're designed to be cheap to produce, be cheap to produce, survive a modest number of connect - disconnect cycles, and be cheap to produce, in that order. None of those attributes really make it a good, robust, fit-and-forget option.

I prefer something like a JST XH connector - 2.5mm pitch, polarised, latching, and readily available.

[jmaja]

None of those attributes really make it a good, robust, fit-and-forget option.

I prefer something like a JST XH connector - 2.5mm pitch, polarised, latching, and readily available.

I have made 100+ of these since 2007 and had zero failures with mini USB. Several cables has been replaced due to damage outside the enclosure. Thus I don't see a problem with robustness of mini B in this use. It's just the need for trimming in order to fit through the cable gland and also maybe space taken inside the enclosure.

JST XH is not something most users can install them selves when a cable needs to be replaced.

[sparkydog]

I'm not sure I understand what you're asking, so please pardon me if I'm just way off, here.

Do you mean you have a cable that is connected to your PCB, which passes through the waterproof enclosure?

If this is the case, why not just use an IP-rated socket, which a) can connect to your board however, and b) will almost certainly never need to be replaced because the fragile parts aren't exposed? Then your user just plugs in their own cable to the socket on your enclosure. (If you need water resistance during use, you would need an IP-rated cable for this also, but those are obtainable. The pool of replacement candidates would be limited, but they *do* exist; for example, this one. It looks like the sockets may even be standardized.) For that matter, there are sockets that just take some other cable on the other end, which would allow the interior cable to be replaced.

[Cramer]

Just a heads up here, as a manufacturer myself, in the very near future (2024) the EU will be requiring all USB to be of the "C" variety. This really can hurt hurt those of us who do sell to that market and have to redesign everything from the ground up.
Thanks Europe!

[AndyC_772]

The requirement is that USB-C is used as the charging port for certain specific categories of device - phones, cameras, that kind of thing.

For the most part those devices tend to use a USB charging connector anyway, the only notable exception being Apple. The consumer product space being what it is, each individual model tends to have a fairly short commercial lifespan before being replaced anyway.

Unless you do work for Apple - in which case I can hear the world's tiniest violin playing in the background - I'm surprised to hear you're faced with anything other than a very minor redesign, if indeed your product is impacted at all.

What's the product?

[Alti]

I would have used a standard USB Type-A to Type-B (the one for printers) and clamp a big gland over square overmold of Type-B.

Just get a BIG standard cable gland, not the one where Type-B barely fits but where skinniest Type-B seals barely. Biggest, another words.
If you want this thing to be IP67 and serviceable and not single use, I'd also consider providing a schrader valve stem for user testing.

[jmaja]

Do you mean you have a cable that is connected to your PCB, which passes through the waterproof enclosure?

If this is the case, why not just use an IP-rated socket, which a) can connect to your board however, and b) will almost certainly never need to be replaced because the fragile parts aren't exposed? Then your user just plugs in their own cable to the socket on your enclosure. (If you need water resistance during use, you would need an IP-rated cable for this also, but those are obtainable. The pool of replacement candidates would be limited, but they *do* exist;

Yes, that is the case. The device has a fixed USB cable running from the PCB through the enclosure to a PC. The device is used outside and in marine environment, thus could be dropped to water etc.

It's not that common to damage the cable. Many of the 15 year old ones still have the original cable. Thus it's not that big of a problem, but I'd like to keep them in service for a long time.

I'll look through the available connectors.

[ajb]

"Split" glands are available, have you looked at those?  Some of them have a standard bulkhead fitting/nut with a split rubber bushing, so with those you'd need to select one where the connector will still fit through the nut.  But there are also ones where the whole assembly splits open, which wouldn't have that limitation.  In general they should still seal up as normal once tightened, but be sure to check the exact rating to ensure it will meet your needs. 

Random example of the first type, lots of sizes listed in the datasheet: https://www.mouser.com/ProductDetail/Heyco/M3234GBJ?qs=5cwIErt2AwRR3TZVllDl3g%3D%3D

[tooki]

I'm designing a PCB, which will be installed inside an aluminum enclosure and needs to be IP67. It has a permanently connected USB cable. In the previous model I used a FTDI module, which had a mini USB B and thus the cable needed to have a mini USB A end. The problem was it won't fit through a reasonable size cable gland without tapering the plastic off the connector (not necessary to remove the actual metal connector with M12 cable gland). Only 12 Mbs is needed.

Now I will use a FTDI chip on PCB thus I can freely choose how to connect the USB cable. What would be the best option? It would be nice, if the user could replace the USB cable when damaged. The PCB will be hand soldered.

Would a screw terminal block work just fine? Or is it better continue using USB mini?

For using mini I'm wondering how freely can I choose how far from the PCB edge the connector is placed. I would probably use the THT version. Some datasheets give 2 mm extension outside the PCB edge and some don't even show where the PCB edge should be. It would actually help if the connector would be totally on top of the PCB. Is there any other limitation to that except that at some point the USB mini A plug plastic will hit the PCB edge?

I don’t know why you’d use mini-USB. Of all the available USB connector types, it’s the least compelling. It’s smaller but less reliable than the standard B connector, but is bigger and less reliable than micro-USB or USB-C.

I wouldn’t use a terminal block. The aforementioned JST XH is fine, as are numerous small connectors. But I, too, would hesitate to call them user-serviceable.

Does the external cable have to be permanently attached? What I prefer doing is to use a panel-mount USB jack or feedthrough, so that the user can attach a cable themselves. As others have said, they do make waterproof versions of these.

[Someone]

Does the external cable have to be permanently attached? What I prefer doing is to use a panel-mount USB jack or feedthrough, so that the user can attach a cable themselves. As others have said, they do make waterproof versions of these.

Even "brand name" Amphenol LTW are not that expensive, and have pre-terminated bulkhead connectors.

[jmaja]

I don’t know why you’d use mini-USB. Of all the available USB connector types, it’s the least compelling. It’s smaller but less reliable than the standard B connector, but is bigger and less reliable than micro-USB or USB-C.

I wouldn’t use a terminal block.

Does the external cable have to be permanently attached? What I prefer doing is to use a panel-mount USB jack or feedthrough, so that the user can attach a cable themselves. As others have said, they do make waterproof versions of these.

Actually mini USB plug is smaller than USB C, which is thinner, but wider. A mini USB (moulding removed) fits through a M12 cable gland, which typically is 8 mm. USB C doesn't fit. Micro would fit as well. The full size A plug is probably too long to be connected inside the enclosure, which is quite small. The distance from the PCB edge to the enclosure inner wall where the cable gland is is about 43 mm.

I have never broken a USB mini connector or a plug. Inside the enclosure it will be used less than 5 times in a lifetime so all it needs to do is keep working while connected.

Why not use a terminal block? Signal quality? Is that an issue at 12 Mbs?

No, the USB cable doesn't have to be permanently attached. It has been just a simple solution to get IP67 with minimal costs.

Are those panel mounted jacks IP67 without a cable? Is there always a cap? Do they corrode after splashes of sea water? All that has been rather easy with the old solution.

[jmaja]

"Split" glands are available, have you looked at those?

No not really. Interesting option. They seem to be quite big though. I don't know, if the enclosure has enough room. At least I don't have tools for making holes for them. I can make M12 threaded hole in aluminum quite easily with a simple drill driver.

There seems to be even ones where the whole body can be split as well. But haven't found anything smaller than M20.
https://www.automation24.co.uk/splittable-cable-gland-pflitsch-uni-split-gland-usg-22554-pc

[Cramer]

Product is Radiation Detectors. I have an inquiry to the EU governing board about this issue.

It's not a minor change, our molds, PCB's, and supporting chips all need a redo. Apple is also being forced to use C connectors in the future also. (insert small violin here also)

I get the idea of having one style of plug. Should have been done years ago. So much waste is produced.

[jmaja]

Product is Radiation Detectors. I have an inquiry to the EU governing board about this issue.

Shouldn't consider your product. It's about "radio" products and laptops and only considering charging.
https://data.consilium.europa.eu/doc/document/ST-10713-2022-INIT/x/pdf

[tszaboo]

Just a heads up here, as a manufacturer myself, in the very near future (2024) the EU will be requiring all USB to be of the "C" variety. This really can hurt hurt those of us who do sell to that market and have to redesign everything from the ground up.
Thanks Europe!

I just had the third meeting about how much paperwork we have to produce to enter the US market. You guys didn't even hear about harmonized standards, and every notified body has their own version of the standards they use. I had to fill out 20 pages of application forms only for FCC.

[thm_w]

If you want cheap and have board space, put a micro-USB (12 pin) and a type-C footprint side by side. Gives you both options.

I wouldn't screw around with JST, or terminal block, as you'll need to custom order the cable.

[Skashkash]

Would something like these meet the environmental rating?

https://www.datapro.net/products/ip67-waterproof-panel-mount-usb-micro-b-2-0-male-female-extension-cable.html

Can also shove a rubber plug in there when not in use. 
Might be pricey though.

[Cramer]

Product is Radiation Detectors. I have an inquiry to the EU governing board about this issue.

Shouldn't consider your product. It's about "radio" products and laptops and only considering charging.
https://data.consilium.europa.eu/doc/document/ST-10713-2022-INIT/x/pdf

We have a Blue Tooth module in our instruments and therefore fall under the RED directive. I am studying more on it, like, maybe we get rid of the BLE chip, which hasn't really increased sales anyway. I do see an annex concerning devices that don't charge, but it is rather ambiguous. What a pain!