Taking A Public Transit Display From Project To Product

We’ve noticed an uptick in “project to product” stories lately, which seems like a fantastic trend to us. It means that hackers are turning out projects that really resonate with people, to the degree that taking the leap and scaling up from a one-off to a marketable product is worth the inherent risk. And luckily enough for the rest of us, we get to learn from their experiences.

The latest example of this comes to us from [Stefan Schüller], who from the sound of things only reluctantly undertook the conversion of his LED matrix public transit sign into an actual product. The original project had a lot going for it; it looked fantastic, it was technologically simple, and it provided a valuable service. But as a project, it made certain assumptions and concessions that would cause problems when in the hands of a customer. Chief among these was the physical protection of the fragile LEDs, which could easily shear off the display modules if bumped or dropped. There were also firmware issues, such as access to the backend API that serves the transit data; requiring each customer to sign up for and configure their own API key is a non-starter for a product.

In the article, [Stefan] enumerates a long list of problems that going from project to product raises, as well as how he addressed them. The API issue was solved by implementing his own service, which acts as a middleman between the official API and his customers. A nice plexiglass and sheet-metal frame serves to protect the display, too. Design changes were made as well, not only to provide better functionality but to make manufacturing easier. [Stefan] also relates a tale of woe with regard to getting the display’s app into the app stores, something that few of us have to deal with when we’re just fiddling around with something on the bench.

All in all, [Stefan] does a great job walking us through the trials and tribulations of bringing a product to market. There are similar lessons in this production run scale-up, too, but with an entirely different level of project complexity.

16 thoughts on “Taking A Public Transit Display From Project To Product

  1. Is EMC testing for this kind of product not required in Switzerland?

    My understanding is that if you tried to make something like this in the US, even though the ESP32 module is already FCC *certified*, you wouldn’t be able to legally sell it to consumers without having the entire product *tested* since it uses high-frequency digital signals.

    1. “I stuck with an ESP32 module because those are already CE certified and with such a small run I did not want to spend money on getting my PCB CE certified.”

      Pretty sure what he wrote is correct.

      A colleague of mine sells equipment he makes. All his equipment is “certified”. He explained he doesn’t need to test anything to get it certified, he only needs to be able to explain why it shouldn’t cause problems.

      Now I might be totally wrong, but I don’t see what part of the display itself could cause those high-frequency digital signals. Because it would then need to be inside the display as the PCB is already certified.

        1. Are you sure you want to do that? How many do you intend to sell? If you want to test thouroughly (accredited measurements) in Switzerland incl. ETSI EN 300 328 be prepared to drop 10kCHF+ ;)

      1. This incorrect. Even if all your individual components are CE certified it doesn’t mean your final product will be. It’s difficult to predict the interaction between different components of your assembly regarding EMC. If your module is CE/FCC vertified it’s less costly to properly certify but you still have to do it.

        Again if you only sell a handful then it is more sensible to omit all the measurements. If you sell 10000+ then it’s a different story.

      2. > Now I might be totally wrong, but I don’t see what part of the display itself could cause those high-frequency digital signals.

        Isn’t the interface between the ESP32 and the display digital?

        Like I said, I don’t know how things work in Switzerland. In the US, basically any circuit that operates at >9kHz is considered an “unintentional radiator” and needs to be tested before it can be legally sold — even if individual *components* of that circuit have already been certified and/or tested.

    2. Technically testing is not strictly required for CE as it is a self declaration of conformity. Most of the cheap china imports such as the used led panel is most likely not tested either. The problems will come when your device emits so much that it disturbs other equipment and the goverment agency investigates (BAKOM). If they find out you imported or built a strong emitter the fines can be very hefty. It is possible that this project would fail EMC testing but in the end the chance that the emission levels are so high to distub other equipment is pretty low.

        1. I would advise you to not even look into certification. It’s a big ordeal if you want to do it correctly and very costly (the EMC lab i usually go to is 350CHF/h radiated and 250CHF/h for everything else precompliance). For the power supply I completely agree. If you sell it you’re legally the importer and thus carry the risk if the PSU from China is dangerous and someone gets injured. (And this is the case sometimes). I would get a few Meanwell PSUs (GSM series for example) and stay below 75W for the PSU.

          1. But still, there are two ways on how to do this.

            1) You can go to a certified EMC lab to get full certification with measurement protocols and everything. They might just give you “not passed” and an expensive bill. This is usually not the first step.

            2) you can do a self declaration.
            It helps to have been in a measurement chamber for pre compliance testing. This gives you an indication how far off you might be (if at all). If you are convinced that this is good enough (for private use, or to industrial standards) you might not need to go to expensive certified lab testing. And you can still sleep well that you did not put out hundreds of dangerous goods

      1. There are safety and emissions components to the CE certification. Several IEC standards that need to be followed. For something this simple, self certification is the way to go, but you should try to back it up with some data in case you’re asked. Some sort of basic EMC testing, and results would not be a bad idea, even if it wasn’t done at a formal test lab. The safety side is fairly straightforward, but I would make sure that your power supply is a “name brand” and not something off of AliExpress. It’s not unheard of for the less well known manufacturers in China to fake the certification logos.

  2. Re: iOS App Store
    A colleague of mine just went through this process. To say that Apple’s process is labyrinthine would be understating it. It took many tries, and each time, the application was denied with only a very cursory explanation of why. He finally managed to jump all Apple’s hurdles, which involved creating an LLC, and got the app into the store.

    For a proof of concept device and app which will never be sold.

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