I actually went with a design like you proposed in the first iteration. It turned out to be more time consuming than the SD card solution, specifically for my non technical SO. Now, she just stuffs an SD card into her laptop, transfers files, puts the card into a prepared cartridge, and sticks a label on it. The cartridges can be ordered fully assembled, so she doesn't have to solder anything.

With a fully mechanical solution, she would still have to extract the SD card from the player (or I spend considerable more effort on the software side, so the device can somehow also act as a mass storage device when connected via USB, givng access to the internal SD card), print or construct the "key", stuff the key into a cartridge and label the cartridge.

There's no great practical difference. The only difference is a higher per cartridge cost. Since that's around €2.50 and could be further reduced by bulk orders, I was fine with this design decision.

The ESP 32 has Wi-Fi. You can just connect to it and upload the next track.

So your easier solution is adding an entire network stack, getting it to connect to your wifi, adding a server and client component?

Duuuuude. What?

You gotta be joking ? instead of custom soldering PCB boards, you just put some magic numbers inside of a machine. What do you mean an entire network stack? It’s an ESP32, there’s 10 samples on doing exactly this on github

A couple of years ago, inspired bu the Tonie box, I built a similar yet much simpler device for a toddler in my family but without such a lofty goal of the learning experience.

I wanted to retain the same "always offline" and "physical" aspects of the experience. I used NFC labels hidden under the cover art label on old (edit: not SD) CF cards because I had a bunch of old ones around and they were all standard size and not easy to swallow. An internal microSD that held all the files needed. Plugging the cartridge in the fake socket which was actually just a hidden power on switch would trigger the playing of a specific file. It's a tad more maintenance heavy but much quicker to pull of.

That’s essentially what Tonie boxes do. They have internal storage and NFC stickers on the figurines. The box is then caching on the SD card and playing from their based on the ID on the NFC chip. If you take the box offline, it can still play the stuff on the box because of that.

With the very big difference that in my case it never needs to (or can, really) be connected to a network and someone else's service [0]. Only to the "parents' service", which was a more convoluted experience for them. They had to manually transfer the file to the internal memory, link it to the NFC label, and print an appropriate cover art label.

It was also interesting to see that when all the kids were gathering around with their toys they were all gravitating towards the one none of them had. But that was an unintended side effect.

[0] When I first heard of Tonies my mind jumped at the idea that the content is stored on the figurine and somehow wirelessly transmitted to the box. The child, parent, and engineer inside me were all thoroughly disappointed this is not the case, and even more so at the perspective of the service being stopped one day or who knows, monetized more aggressively.

There is one advantage of this though, via the tonie app you can change to separate episodes from the same series without buying additional figures. I'm a network security guy, somehow, and I'm sort of OK with the tonie box. Alexa etc, no way, but it seems not entirely bad.

We have a Yoto player, which works ina similarly (NFC chip as a “pointer into their web service, content cached on the device). I was pleasantly surprised to see that they promise that it’ll will work for at least five years after they stop selling the current version.

> I was pleasantly surprised to see that they promise that it’ll will work for at least five years after they stop selling the current version.

That disclaimer makes me even more uneasy. It implicitly says the toy might stop working after. You bought a toy, you didn't rent it or buy toy-as-a-service. There's no reason the device shouldn't work forever or for as long as it's in good enough condition to operate. And there's no reason you shouldn't own the content on that toy or be free to supply your own forever.

If you buy an audio cassette and a player they work until they fall apart. Here you need to rely on the goodwill of the seller to allow you to keep using them as long as they don't compete with their newer product too much.

I strongly believe that the better option for anyone who can opt for it is something that relies on no online components even if it's more elbow grease for the parents.

To me, a Yoto is a toy-as-a-service. And for what it does, I don't mind. The tradeoffs for what I'm buying are OK to me in this situation.

I'm fully aware the content on these cards will one day go dark. For content I really care about, I'll make sure I purchase that content another way. Often by buying the actual physical book.

But my family doesn't need every children's story book to last forever, we don't need every kids toy to become generational artifacts.

The device has a lot of online "radio" content as well. Those change on a regular basis and once they're gone, they're gone. That's OK to us in the end. We use the app to mess with these boxes as well and listen to the content we bought on cards through the app in the car as well.

If Yoto disappears tomorrow and the boxes fall silent, sure I'll be disappointed. And yes, potentially they could have made them another way. But nobody on the market today makes something as durable, easy to use for a child, and have such a good content library while also making that content 100% offline. The kids are too young to realistically be handling CDs or vinyls. Eventually the kids will age up into handling CDs for listening to content they own, and they already do have some CDs and vinyls but that's currently a "mom and dad handle loading it" situation.

I totally get things like Tonies and Yotos are the embodiment of DRM hellscape. But assuming you go into it eyes open, its an ok trade in my book. Its not like that's the only way to consume media. And in the end, with the license for the media attached to physical cards, its easy to trade/sell/buy the content second hand from friends and other families around. And since its so durable, even though a toddler handled it for a year or two it's still in perfectly fine shape. Have a two year old handle a CD on their own for a year and see how well it holds up.

Why not just put an RFID reader in the box and an RFID tag on each cart? The reader modules are sub $10, and the tags are a few cents.