Marelleo, a story box I built for my kids

It started as an irritation on holiday Last summer, on holiday with friends and a small tribe of children, I came across the Toniebox. And honestly, I thought it was great. The child puts a figurine on the box, the story starts. They take it off, it stops. No screen, no menu, no parent to go and fetch. A two year old gets it in one second, which is roughly the highest level of usability anyone can reach. The gesture is perfect. The business model, much less so. All these boxes work the same way: the object sells for a more or less reasonable price, and the money is made afterwards, on the content. Whether it’s the Lunii and its closed catalogue, the Yoto and its card packs, or the Toniebox and its figurines, every new story is a purchase, from a catalogue I don’t choose, on an object I don’t control. You’re not buying a player, you’re buying a subscription dressed up as a wooden toy. And that genuinely annoys me. Meanwhile, I had been telling myself for years that I wanted to do electronics. Not as a dabbler: actually understand it. Except I knew nothing about it. I own a soldering iron that comes out every three years to reattach a headphone wire, never to build anything. The kind of guy who knows what a resistor is without ever having had to choose one. The two urges met in the car on the way home. That would be my project. An RFID reader, a tag, a box that plays an audio track depending on what you put on it. Not to make a product. Just for my kids, and to learn. Two discoveriesv0 The breadboard, or the right to get it wrong I already knew what I didn’t want. A Raspberry Pi is a full computer just to play an MP3: too big, too hungry, and it takes twenty seconds to boot. A child putting a figurine down does not wait twenty seconds, they wander off and play. At the other end, the genuinely low level chips, the ones you program in C with a 400 page datasheet, are far too steep for a beginner who would like to hear a story that same evening. While reading around, I came across the two things that made the project possible. First the ESP32 development board: a microcontroller with WiFi built in, beefy enough to decode MP3, simple enough to program like an Arduino, and sold for a handful of euros. Then the breadboard, that perforated plate where you push components in without soldering anything. It sounds like a detail. It is the whole project tipping over. On a breadboard, getting it wrong costs nothing: you unplug, you start again, nothing is damaged. When you’re learning, that is exactly the property you need. So I read documentation, I talked it through with Claude, I drew wiring diagrams in a notebook. And very quickly, far too quickly to feel earned, I had a circuit that played an audio track when you put a tag on it. It was ugly, a plate of copper spaghetti, the speaker lying bare on the table.

But it worked.

A few hours, and I had a thing that told stories. I don’t think I had been that pleased with something made by my own hands since childhood.

The first circuit.

An ESP32 on the breadboard, the NFC reader at the end of a few wires, a red LED saying it's alive.

Not a single solder joint.

What caught fire The potentiometer, the smoke, and the smell of ski wax What came next is less glorious. To set the volume I added a potentiometer, that little rotary knob which is nothing more than a variable resistor. Except that wired wrong, it no longer sets anything at all: it becomes a plain wire between plus and minus. That has a name, it’s called a short circuit, and it heats up terrifyingly fast.

It smoked.

And it gave off a very particular smell, which took me a good while to place before it hit me all at once: ski wax.

Burning wax.

I recognise it instantly now, and it is never good news. The battery was the other piece of work, and the one that made me think. You don’t connect a lithium cell to two wires and move on. You need a charge controller, a dedicated chip that decides when and how to fill it, that stops at the right moment and cuts out before anything stupid happens. You also need to fasten it down properly, because a lithium battery rattling around inside an enclosure and getting pinched is precisely the scenario in those videos nobody wants to watch. And then a stupid detail: my battery’s connector did not match the one on the charging board. Two little white plugs that look alike, two different pitches, incompatible. So I did what you do at eleven at night on a Tuesday when you’re nearly there: I cut the connector off and soldered the battery straight on. Immediate consequence, which I had not seen coming: no connector any more, therefore no way to unplug anything, and no switch anywhere in the circuit. The box was permanently on. Twenty four hours a day. A lithium cell hastily soldered into an object that never turns off, sitting in a child’s bedroom. Written down like that, it needs no comment. That is the moment I stopped treating this lightly. Not out of fear, but because I understood that I was no longer tinkering with a gadget on the corner of a table: I was placing an electrical object into my children’s daily life. Everything else in the project follows from that realisation. Workshop notev1 From breadboard to perfboard The first consequence was leaving the breadboard, and it wasn’t only about safety. A breadboard holds by friction. Every wire is held by a tiny spring, which is wonderful for trying things and disastrous for lasting. Move the circuit and a contact is lost, and the fault that follows is far worse than a clean failure: it is intermittent. You hunt a bug in your code for an hour and a half, you reread the same function twenty times, and it’s a wire that no longer touches.

The same circuit as on the breadboard, but soldered.

It survives being moved across the table, which is already a lot. The next step is perfboard: the same grid of holes, but on a printed circuit, with every component soldered in. You lose the right to be wrong, you gain a circuit that holds together. That’s where I really learned to solder, and above all where I understood that my repair soldering had nothing to do with manufacturing soldering. Repairing is remaking a joint that existed. Building is making a hundred in a row, all clean, all identical, knowing that the hundred and first is the one that will fail.

Without him I would still be cutting cardboard with a ruler. I drew my models in Fusion 360 on the free hobbyist licence, and printed.

The enclosure in Fusion 360.

The circle on top marks where the figurine goes, the hole beside it takes the button, and the slot on the side lets the USB-C through.

The first version was too big and too fragile.

And quality control arrived faster than expected, in the shape of three children aged 21 months, 5 and 7.

They broke the knob by turning it like animals.

The volume knob ended up spinning with no end stop, round and round, and as it turned it wound the wires around themselves until it tore every one of them off. I opened the box onto a little nest of twisted copper. That’s where I learned the most important rule of the entire project: a five year old does not turn a knob, they unscrew it. And they don’t stop when it resists.

They stop when it gives. The potentiometer and its five tabs: three for the volume, two for the switch that turns the box off at the end of travel. Those are the wires that wound themselves up. So I started over.

I took every measurement again with callipers, component by component, so that each hole would land exactly where it should and each part would be held by plastic rather than by its wires. I thickened the walls, added pockets, lowered the height. Version after version, the object stopped looking like a prototype and started looking like an object. Still in the spirit of nothing being allowed to give, I also abandoned self tapping screws. Screwing straight into printed plastic holds once, twice, and on the third go the material splits along the layers: the hole holds nothing any more and the part is fit for reprinting. The real answer is called a brass insert. You set it on the hole, come down on it with the tip of the soldering iron, the brass heats up, melts the plastic around itself and sinks in. As it cools you have a metal thread captured in the part, which you can screw and unscrew a hundred times.

The brass inserts sunk in with the soldering iron.