What I learned selling 2,500 MIDI recorders: Hardware is not so hard

What happens when app is outdated and can't be installed to current android os?

Yeah, hardware is indeed not too hard if you have a trivial hardware project and ignore all the hard stuff.

Complexity-wise this is probably the easiest board one could imagine. It's an off-the-shelf MCU module, a 1:1 copy of the MIDI circuit from the specification, and some ports wired straight to the MCU. Throw in a trivial I2C-connected RTC and HSM for good measure. You could probably design this in an afternoon. But indeed: that is a good thing. Not everything has to be complicated, and plenty of people are willing to pay for simple products.

On the other hand: what is the cost for that?

The USB-A Host port has ESD protection, but as far as I can tell MIDI Out and SD do not. Sooner or later this will result in some static-prone user frying their expensive board. Have you got a proper Customer Support / aftersales pipeline yet? How many units did you reserve for warranty replacement? Luckily you've got a huge margin, so a few replacement boards shouldn't bankrupt you.

Similarly, the MIDI ports seem to be using low-double-digit series resistors for the MIDI Out current loop - in 0402 form factor. As the spec says: short the port and they'll draw over 0.5W, which a 0402 can't dissipate. To be fair, the exact circuitry is a bit hard to tell from the image, but will this mean they'll catch fire?

The AMS1117 is also an interesting choice. It's a classic option so it is often seen in beginner tutorials, but it is absolutely terrible[0], and with the capacitors used you shouldn't be surprised to eventually run into stability issues. It might work Just Fine for 99% of units, but the 1% will have weird undiagnosable heisenbug issues.

From a UX perspective I'd also question the use of a coin cell battery for the RTC: it'll eventually run dry or even start leaking. A supercap would've been a more durable and convenient option - especially considering the "always leave it plugged in and forget it" use case. Or, if you need a battery anyways: go for li-ion so it can be used on-the-go. Similarly: USB-B for Power In in 2026? That's just lazy. USB-C is trivial to add with a 5-minute-guide and would've been cheaper. The USB-A Host port is just about excusable, though: doing that in USB-C is a bit harder. And the Power In port not being usable for a connection to a host PC and telling people to buy some sketchy adapter on Amazon? Understandable considering the MCUs peripherals, but a disappointment.

And then there's the elephant in the room: certification. It seems like you just... didn't? Which is understandable for a small hobby project! But making it EMI/EMC compliant is by far the hardest part of designing market-ready products. You can't just completely ignore all the stuff involved in making it compliant with FCC/CE/UKCA/whatever rules and call it "not so hard". It's the difference between baking a pie for your birthday party, and opening a bakery.

Your hardware project wasn't hard because you've only done the easy stuff. And kudos for shipping - many people don't make it even remotely this far. Especially using an injection-molded housing is quite the achievement! The startup costs for that make it a real showstopper for many small-scale projects, and making mistakes can easily bankrupt you.

But this is where the actual adventure starts: scaling it to 25k / 250k units. You basically have to start from scratch and do 10x as much work. Meanwhile, China is pumping out $10 clones for your $250 recorder. Sure, you put DRM in it, but is your software moat really wide enough to protect you?

Many congratulations on your achievement, but please understand that writing this blog post is almost naively premature. The hard part hasn't even started yet.

[0]: https://www.reddit.com/r/esp32/comments/1m7ne4i/psa_avoid_us...

Assuming this is just standard 2.0 speeds, it should be nothing. It adds a slightly more expensive connector and 2 resistors… and that’s it.

While I'm typing, I'm not just thinking about which keys to hit. I'm thinking about how I'm using a function and what the inputs and outputs are. I'm debugging in my head, I may realize the code isn't going to do what I thought it would. Or I'm realizing that what I'm doing isn't going to scale and that I need a more rigorous approach. Often, I'm thinking "wow I'm going to have to type this same block a bunch of times, I should make a new method/function to handle this."

With code, I'm not planning everything down to the finest detail before I start writing. I know what I ultimately want my code to do but there are many unknowns I hadn't considered. Coding with an LLM is different depending on how you use it. When I'm using code completion, that's usually just helping me prevent syntax errors or to write an efficient snippet of code without having to check docs. But when I tell Claude "I want a web app that does xyz" and it creates it whole-cloth, that takes away the challenge of learning something new and building. I'm not a web developer and anything I could create is going to take me a long time to make (and it probably won't work well or look good) but Claude cranks it out with ease. I get to play software project manager and let the expert do the technical work. It's kinda fun being able to quickly get resulrs. Rather than debugging individual lines of code and thinking about the best way to implement code, I get to test features and think about better ways for the overall system to operate.

> 99.99% of cheap Chinese products you buy on Amazon don't actually have this testing done at all. So by doing any testing you're already way above them.

Yeah, but those Chinese dropshippers don't have significant local presence. If they are caught doing shady stuff they'll just let their $100 letterbox company go bankrupt and start over.

You, on the other hand, would actually have to pay whatever fines some regulator charges you with, because you are physically present in a jurisdiction they can apply power to. This makes self-certification a bit of a footgun: you essentially pinky promise that you fully understood all the relevant rules and regulations, and otherwise pay what in the worst case might be a hundred-thousand-euro fine. Quite a bit of a gamble!

The main saving grace is of course that the authorities are way too busy to investigate some random guy selling a handful of devices from his kitchen. But get too successful, and some competitor might just decide to give them a little hint on exactly what part you missed because you didn't even know you had to comply with it.