Live on CrowdSupply! muArt - A UART converter finally done right

[T3sl4co1l]

Digi-Key does value-add enclosures, FWIW.  I haven't quoted them yet but it can't be too horrible.  I'd think it's worth looking into for 100s+.

Labels are easily printed, as well.  The combination very easily looks pretty sharp:



Tim

[Cerebus]

I meant insulation indeed. Funny that my native language (which more or less obviously is not Englisch) does not have separate words for isolation/insulation.

How are we to know? Your name, Ogden, is a fine old English northern surname, you haven't set your country in your profile, and your English is considerably better than that offered up by certain native English speakers on this forum. So, no, it's not obvious that your native language isn't English. However, guessing: Verstehen Sie jetzt?

[DTJ]

Following along.

[sequoia]

No DSR?    On adapter like this  at minimum I'd like to see both CTS/RTS and DTR/DSR pairs, and ideally all signals...

[Maxlor]

Case wise, using a potting box with the PCB as top cover (like Dave's µCurrent) would seem like a good and cheap solution. I've used that technique myself for low count projects (5 pieces), and I was happy with how it turned out. It certainly helps to mitigate ESD stuff and improves general mechanical robustness if you can't actually touch any circuitry and only the connectors are exposed.

[ogden]

I meant insulation indeed. Funny that my native language (which more or less obviously is not Englisch) does not have separate words for isolation/insulation.

How are we to know?

Educated guess that author of the post is not so dumb to imply that heat shrink adds galvanic isolation to the USB-UART interface? What remains is typo or illiteracy

Case wise, using a potting box with the PCB as top cover (like Dave's µCurrent) would seem like a good and cheap solution.

Interface adapter shall be small and shall not mind top or bottom orientation. This is one reason why for stm32 playground projects I stopped to use J-Link but use cheap 3$ ST-Link knockoff instead. It takes virtually no space on the table, can be rotated as you (your device) wants. Thou said ST-link have metallic enclosure which is no good. Enclosure of interface converter shall be made completely out of insulator so you can drop it INTO live device w/o danger of shorting something and blowing-up.

[Navarro]

I already have something like this designed: https://github.com/PY1CX/Quad-Serial

There is some things that I wanted to change in a next version but this can be an example.

[Cerebus]

I meant insulation indeed. Funny that my native language (which more or less obviously is not Englisch) does not have separate words for isolation/insulation.

How are we to know?

Educated guess that author of the post is not so dumb to imply that heat shrink adds galvanic isolation to the USB-UART interface? What remains is typo or illiteracy

I meant "How are we to know [that you're not a native English speaker]?"

As to the latter, it wouldn't be the dumbest thing we've seen on here.   The rule seems to be "never underestimate human stupidity" and "never underestimate some people's total inability to actually explain what they mean".

Interface adapter shall be small and shall not mind top or bottom orientation. This is one reason why for stm32 playground projects I stopped to use J-Link but use cheap 3$ ST-Link knockoff instead. It takes virtually no space on the table, can be rotated as you (your device) wants. Thou said ST-link have metallic enclosure which is no good. Enclosure of interface converter shall be made completely out of insulator so you can drop it INTO live device w/o danger of shorting something and blowing-up.

I've got a bunch of those, worth more than the $2-3 they cost. They have anodised aluminium cases, and aluminium oxide is a very good insulator. I just slapped the 4 wire probes across them and my meter can't see any conductance - sticks on OL on the 200MΩ range - so I don't think there's any worries there.

[Mr. Scram]

On the topic of a case: yeah best would be to have one too, but the options are:

• Let a case of my own be manufactured. Too expensive below 10.000pcs, so not an option.
• Design into an existing case. This would still need to be modified with cutouts for cables and windows for LEDs plus printing for labels. Also, the board is pretty small, so a standard case would make it a lot bulkier (and uglier).
• Design and 3D-print the case myself. First, I have no experience with mechanical design, and second I don't have a 3D printer.
• Ask for help in design, and share the design so that anybody can print their own case. This is not so bad, but most people still don't have a 3D printer, so only a few would be able to benefit from this solution.
• Apply heatshrink. Might not be "professional", but TBH it works, it is cheap, and is available for everybody. And as already pointed out, not so ugly as long as transparent.
• Apply conformal coating to the board. I think this could be workable as far as costs are concerned (though not so sure as it would require a 2-phase assembly), however, this is far too unreliable (abresion, thickness etc.), so I call my veto on this.

Summarizing, only heatshrinking works that I can readily ship to my backers. Having a public design for a custom 3D-printed case would be ultra-cool, but people would need to print it themselves. EDIT: Or, have a backer tier during the campaign where a printed case is included, but sold at a higher price.

You're applying an answer to a question. Having cases made doesn't have to be that expensive, even when numbers aren't huge. Calling conformal coating unreliable doesn't seem to coincide with practical experience.

If you want to pick a solution because you want that solution that's fine, but be honest with yourself about your reasons.

[janekm]

Regarding the case, there are plenty of off-the-shelf cases designed for USB interfacing devices like this.
There's the rather cute one use by the ST-Link clones: https://www.sunrom.com/p/st-link-v2 (anodised aluminium so has the potential insulation issue if it gets scratched), and they're already using the same connector as you are.
Similar plastic versions exist too. Just have a look at the many enclosures designed for USB memory sticks, some of them should suit your project.

Getting cases customised from Digikey is likely to be prohibitively expensive for a project like this.

[Mr. Scram]

Regarding the case, there are plenty of off-the-shelf cases designed for USB interfacing devices like this.
There's the rather cute one use by the ST-Link clones: https://www.sunrom.com/p/st-link-v2 (anodised aluminium so has the potential insulation issue if it gets scratched), and they're already using the same connector as you are.
Similar plastic versions exist too. Just have a look at the many enclosures designed for USB memory sticks, some of them should suit your project.

Getting cases customised from Digikey is likely to be prohibitively expensive for a project like this.

Why insist on Digikey?

[pylo]

You're applying an answer to a question. Having cases made doesn't have to be that expensive, even when numbers aren't huge. Calling conformal coating unreliable doesn't seem to coincide with practical experience.

If you want to pick a solution because you want that solution that's fine, but be honest with yourself about your reasons.

I am trying to be honest, if you are correct and I can make custom cases really cheap, then I just haven't found the right case manufacturer yet. But "cheap" is relative. Many would say 7$ for a custom case is cheap, but when the product without case would cost something between 20-30$, then that 7$ are expensive. I cannot incorporate that into the existing price because then I would be selling the thing below material costs, and increasing the price by the case's could easily take it over 30$, which a lot of people will find just simply too expensive for a UART converter.

As far as conformal coating is concerned, I stand by my point it is unreliable as a replacement for a case, which is what we are talking about here. In itself it is of course reliable when applied for its designated use, that is, for PCBs inside a case for protection against chemical wear/oxidation, increasing insulation etc., but it is not a case replacement. If this doesn't seem to "coincide with practical experience" for you, please show me a commercial portable product where conformal coating was used instead of a hard case.

[pylo]

Digi-Key does value-add enclosures, FWIW.  I haven't quoted them yet but it can't be too horrible.  I'd think it's worth looking into for 100s+.

Hi, thanks for the tip. I've looked into it, what I've found at DigiKey were the Bud Industries cases they are selling in cooperation. I haven't quoted them either, but the prices for unmodified cases (by Bud that you can optionally customize) are online, and they sell for 10$ unmodified. Customized they will surely cost even more. This is unfortunately not acceptable, the muArt is too cheap to have a 10+$ case.

[pylo]

Case wise, using a potting box with the PCB as top cover (like Dave's µCurrent) would seem like a good and cheap solution. I've used that technique myself for low count projects (5 pieces), and I was happy with how it turned out. It certainly helps to mitigate ESD stuff and improves general mechanical robustness if you can't actually touch any circuitry and only the connectors are exposed.

This can work. I can get such cases for under a dollar. This requires a design with double-sided assembly, which means if I go for this solution, I should not sell the muArt without a case. Which if perfectly fine by me, as long as the case is not too bulky.

[pylo]

No DSR?    On adapter like this  at minimum I'd like to see both CTS/RTS and DTR/DSR pairs, and ideally all signals...

DSR, RI and DCD are the only UART signals I haven't made available. If I wanted to make all signals available, I'd need to incorporate a 3rd isolation IC, which is really expensive, for AFAIK barely any benefit. And that'd still be the case even if I left out the GPIOs. Second, I have yet to see any electronics that uses those signals. I know they are part of UART and heard they are used in modems, but in modern electronics I have yet to see a use for them. Even DTR is only around because there are many boards that use them for controlling the RST line during flashing.

Is there some specific reason you'd like to see DSR included? A board that needs it? Or some other (preferably non-exotic) use case I'm not aware of?

[pylo]

I see how many of you are interested in having a proper case. So I'm not giving up on that yet and I am actively looking at different solutions. I have some ideas that need further exploration and have already contacted companies. Give me a week or so and I will come back on the topic of a case, hopefully with some results.

[pylo]

Hi Everybody, I'm just here to give a short update. There is a prototype case in the making, and the layout of the board will be revised to make it nicely mountable inside the case. According to the case's manufacturer, its cost should be fairly acceptable even for this product in the quantity that I set as the goal for the campaign. We'll see, but it surely sounds promising. The revised layout also centers the USB-receptacle, which is better for multiple reasons, new case or not.

As always, I'll be back if there are news or any questions to be answered. I'm listening for your feedback, so don't stay silent if you've got anything to say.

[pylo]

Hi All, I'm here with news again. The first plans for the case are done and it turned out really cool. I've attached a CG render to the OP, go take a look Note that there might be slight differences to the real one, like how translucent the housing really is (I've yet to see it myself), but you get the gist.

There are some nice tricks in there to keep the costs low. The play with transparency and translucency - beside making it look even cooler - helps to keep the labels readable without having to print a silkscreen or stickers, and as a side benefit it guarantees the labels will never come off. There is also no need for windows, holes or separate photoconductive parts just to keep the lights visible. The design is completely screwless, which simplifies assembly a lot.

The layout of the board itself has been revised a bit, but mostly just to center the USB receptacle. It turns out the case itself probably won't need any design changes of the board, so the board is just as compact and neet without the case as it is with it - another big plus. Not to mention the PCB didn't get any larger, quite the contrary, it has become even smaller in this revision. The board is now only 50.2 x 23.5mm, which makes it about the same width as a 2-euro coin, and is about as long as two of them. Since the case is custom manufactured to fit around the board tightly, it doesn't make things a lot bigger either - my point here is, even though the muArt has a lot more components than others and even a case, the high integration and custom case still make it really small, just take a look at the OP's picture to see the comparison with a coin, it is soooo cool... 

By the way, I want to thank tec4data for their design of the case. They will also be the one manufacturing it, and they claim they can keep the costs within my limits, including one-time costs! So a big Thumbs Up and Thanks to them.

Next steps? I should be getting a 3d-printed prototype of the case by the end of next week, that will be the first time I'll have one in my hands. The material will be way off, but hey, the final ones will be injection molded. As for the electronics, because I knew I was going to make changes to the layout, I held up prototype production until now. But unless testing tells me otherwise the board is basically final now, so no more expected delays from this point on. Actually, first thing next day I'm placing orders.

[Monkeh]

Now that's a pretty nifty little case.

[pylo]

Just a small status update since it's been some time. I've ordered the prototypes as promised, in total they ship in about 3 weeks, which means only 2 more left, so I should have them approximately by the end of this month. With them in my hands, I'll be able to test not only the circuit itself, but also how well they fit into the (prototype of the) case. Until then though there isn't too much to report, which is the reason for the apparent silence in the past week. So I guess there will be a lack of updates in the next two weeks too, but just until I receive the units.

Until then you could help me with one thing though. This is my first time doing crowd funding. Where do you suppose I can promote the upcoming campaign (or promote it once it is running)? Any sites, blogs, forums that you think could be interested in the muArt? Hackaday seems like an obvious choice, mikrokontroller.net (a german forum), hackster.io, maybe a reddit etc. Any ideas? I'd also be glad to send one to Dave and others, but frankly I don't know others    I'll have 13 in total (minus those I destroy during stress test  ) and I'd be happy to send out a couple to bloggers and forumers.

[Maxlor]

Sounds cool! Of course, sending a prototype to Dave is a gamble, timing-wise! Who knows whether it'll take 1 or 6 months for him to show your device 

Btw, for those of us that might maybe do something similar, i.e. a small run for some project that others might be interested in, would you be willing to talk a bit about the design process and costs for the case? At least for me it's  surprising that a custom injection molded case is possible!

[MattSR]

Hi Pylo!

Can you share the name of the case manufacturer? I’ve been searching for a very long time for a suitable case manufacturer for a smallish project of mine, and the translucent design you have looks great!

Cheers,
Matt

[pylo]

Hi Pylo!

Can you share the name of the case manufacturer? I’ve been searching for a very long time for a suitable case manufacturer for a smallish project of mine, and the translucent design you have looks great!

Cheers,
Matt

The company is called tec4data (tec4data.com), they are a located in Austria in Europe (I'm from Hungary, so they're relatively near to me). They offer design services and production. Good luck and I hope they'll be able to help you too.

Btw, for those of us that might maybe do something similar, i.e. a small run for some project that others might be interested in, would you be willing to talk a bit about the design process and costs for the case? At least for me it's  surprising that a custom injection molded case is possible!

I'll try, but I'm afraid I might disappoint you. The reason is, I have literally zero experience in mechanical CAD design, so after some consultation with tec4data, they basically did all the work. Nevertheless I know it was a gigantic help for them that I had a proper 3D model of the electronics, including not just the PCB, but also the components on it. So I advice others too to make sure you maintain a nice 3D parts library for your project, so that when the time comes, you can make a STEP file export. The case manufacturer then asked me some questions, like "do I want to keep the pin headers pointing upward", and they also made sure we agree on where LEDs and printed text will be positioned. Actually pretty basic stuff, nothing I was surprised about. I already made prior thoughts about these issues, and since I wanted to keep the PCB in a form where it lends itself equally well to a case-less product as well as one with a case, I already had the answers on me. Then they just did their magic for about a week and came back to me with (again a STEP) model of their design. The rendering that you see in the OP was made by me already, after they explained what their idea about the materials was. I briefly showed them the rendering before posting here just to make sure this is how they also imagined it.

Injection molding is normally pretty expensive. Not the per-piece cost, but the setup and tooling costs. These are usually somewhere in the 5k-30k$ range depending on a lot of things, which is why I ruled it out by experience in the beginning. tec4data will only give me an official quote once we've tested the fit of the board into the prototype cases that they print. I've visited them and they have a crazy large and expensive professional 3D printer locally that they use for prototypes. This is not one of those portable bench-top 3D printers that pop up every week on kickstarter, but one that is in the several hundred thousand euros price range. Needless to say, it prints really high quality (I've seen it!). But back to the original topic, they promised me that the absolute upper bound for the case will be 3$/pcs (meaning it will probably cost less), and that one-time costs will be a lot less expensive than the numbers above so I "need not worry". They said this after I made sure they understand the finances of this project (that is, that it is crowdfunded, the end-user price range, and the likely quantities to be sold). I know this sounds vague, but as I said, I need to wait for the mechanical fit tests, only then will I get a quote. But even then, whatever the prices will be, I will need to ask if their quotation is public - I didn't ask this question yet because there is also no official quote at this point, so it seemed like jumping too much ahead.

[Maxlor]

Thanks pylo, that's very interesting. Not disappointing at all, since I don't really have 3D design/machining skills either. So far I've been matching PCBs to existing cases, it's actually good to hear that it is possible to do it the other way round even if you're not an expert.

I think it's pretty cool of them to do this much for you, when there's no guarantee that the crowdfunding will work out. What did you tell them that your minimum order count was going to be? I'm guessing a few hundred pieces, which means a high 3-digit sum for them overall as worst case? From what little I know, that doesn't seem profitable, especially given that they fronted the design work too (don't overestimate that; I've seen how quickly people who know SolidWorks can create designs, I'd guess 1-2 hours for your case? – but of course those people ask for a decent salary too!) So either they think your device is going to be successful and sell more than the bare minimum, or maybe they're hoping to get some word of mouth advertisement through you? Either way, they seem cool, I'm looking forward to reading how it all works out. And of course, you'll have my support once you launch your kickstarter 

[MattSR]

Thanks for the info pylo!

One thing I need for my project is a special connector (with ten contacts and a small screw thread) to be integrated into the case. Through your dealings with them, do you think this is something they might be able to accommodate?

Cheers,
Matt