### Show HN: I Built a Synth for My Daughter

It all started with a simple observation. My four-year-old daughter is fascinated by music, but most of the electronic toys we’ve gotten her are either too simplistic, playing the same three pre-recorded songs, or they’re designed for adults and far too complex. I wanted to give her something in between: a real, hands-on instrument that was simple enough for her to explore without frustration, but powerful enough to feel like she was actually *creating* sounds.

So, I decided to build her a synthesizer.

#### The Goal: Simple, Durable, and Fun

My design philosophy was straightforward:

1. **Kid-Proof Interface:** Big, satisfying buttons and chunky knobs. No tiny screens or complicated menus.
2. **Immediate Feedback:** Every action should produce a sound. Turn a knob, the pitch changes. Press a button, the waveform switches.
3. **Durable Construction:** It had to survive being dropped, smacked, and generally loved by a preschooler.

#### The Hardware: A Mix of Off-the-Shelf and Custom

The heart of the synth is an Arduino Nano. It’s cheap, easy to program, and has enough processing power for simple audio synthesis.

For the controls, I went with:
* **Four large arcade-style buttons:** These are nearly indestructible and have a great tactile “click.” They’re used to select the waveform (sine, square, triangle, sawtooth).
* **Two large potentiometers (knobs):** One for controlling the pitch (frequency) and one for another parameter, like a filter cutoff or modulation speed, depending on the mode.
* **A standard 1/4″ audio jack:** So we can plug it into a small amplifier or headphones.

The enclosure was the most custom part. I designed a simple, sturdy box in Fusion 360 and 3D-printed it using a bright, colorful PLA filament. I made sure all the edges were rounded and the components were securely mounted so nothing would come loose.

#### The Software: Making the Noise

This is where the real magic happens. Initially, I just used the basic `tone()` function in Arduino, which was great for getting started. It produces a simple square wave, and you can easily map a knob to control its frequency.

Seeing my daughter immediately start twisting the pitch knob to create siren sounds was a huge win.

To make it more interesting, I moved beyond `tone()` and dove into a library called Mozzi. It’s a fantastic sound synthesis library for Arduino that lets you generate different waveforms and apply effects. This allowed me to implement the different waveform selection buttons. The square wave is harsh and buzzy, the sine wave is pure and soft, and the triangle wave is somewhere in between. It gives her a palette of sounds to explore.

The code reads the analog values from the two knobs and the state of the four buttons on a continuous loop. It then uses this input to set the frequency and type of the sound wave being generated before sending it out to the audio jack. It’s simple, but very effective.

#### The Result: Joyful Noise

The moment I handed it to her was incredible. Her eyes lit up at the brightly colored box. She didn’t need any instructions. She immediately started pressing buttons and turning knobs, filling the room with a cacophony of bleeps, bloops, and sweeping sirens.

It wasn’t Mozart, but it was pure, unadulterated creation. She was exploring cause and effect in real-time: “When I turn this knob, the sound goes weeeee!”

This project was one of the most rewarding things I’ve ever built. It wasn’t about creating a professional-grade instrument. It was about creating a gateway to creativity for someone I love. It’s a tool for her to make her own noise in the world, and I couldn’t be happier with how it turned out.

I’m already thinking about version two. Maybe a simple sequencer or a built-in speaker. For now, though, I’m just enjoying the music.