The archive · Product Ideas · Product decision · 2025
Alastair Roberts' four-slider synth lets his toddler compose with loops
For his daughter's third birthday, a London engineer built a portable step-sequencer synth whose four sliders set four looping notes — no button-holding needed.
Alastair Roberts
What it had to solve
Alastair Roberts, a London software engineer with no hardware experience, wanted a musical toy for his daughter's third birthday that was simple, tactile and creative — and, crucially, did not require holding buttons to keep a sound going. The trigger was her Montessori activity board of switches and LEDs, which reminded him of a synthesizer's control surface.
How it works
Alastair Roberts, a London software engineer, wanted to give his daughter a musical toy for her third birthday. The idea started a year earlier, watching her play with a Montessori activity board full of switches and LEDs — a control surface, he realised, was not unlike a synthesizer's. The catch: whatever he built had to work without holding buttons down to keep the sound going, which is how most instruments expect beginners to play.
With no prior hardware experience, he learned as he built: from a 15-year-old Arduino Inventors Kit to a custom two-layer PCB pairing an Elegoo Nano with a small SAM2695 synth module and speaker. The finished instrument has four sliders that set four notes in a looping step sequence — slide up for higher pitch, down for lower — plus tempo, volume, scale and instrument controls and an OLED screen whose dancing panda gives visual feedback. Five boards cost £35.41 from JLCPCB, and the enclosure was 3D-printed.
A week after his daughter unwrapped the synth it was in regular use on her toy shelf, holding up well. He published the full story with a demo video in November 2025; Hacker News gave it 1,278 points and 209 comments in days, Hackaday covered it as a labor-of-love build, and adults without musical training said they would love one too.
Why it lands
- Sliders map to a toddler's existing abilities: sliding up and down is easier than pressing keys in time, so the instrument fits the child instead of demanding piano technique.
- A looping step sequencer removes the hardest part of music-making for a small child — timing — while still letting her shape melody and watch the result.
- Tactile controls plus immediate sound and a screen character make the toy rewarding to explore without instructions.
- The design was deliberately shallow enough to fiddle with at first but deep enough to stay interesting as she grows, so one product spans several ages.
What it did
The write-up reached 1,278 points and 209 comments on Hacker News within days of the launch and was covered by Hackaday; non-musician adults said they wanted one too, and the author began weighing a polished open-source version or a small Kickstarter batch.
What you can take
Match the interface to the child, not the instrument: sliders plus looping make music possible before fine motor control or timing exist, and the same toy keeps depth for later.
Since then
After the launch, Roberts kept the project as a learning build while noting the gap between a great toy and a product: certification such as UKCA, CE and FCC can cost £5–10K or more, injection-molded tooling is expensive, and a small run would need capital he was not ready to commit. He planned to upgrade the Elegoo Nano to an ESP32 to simplify firmware and open up better display animation, and said a polished open-source version for makers, or possibly a small Kickstarter, could be the next step if interest held.
Sources
- I Built a Synth for My Daughter
- Baby's First Synth Was Daddy's First Project
- Show HN: I built a synth for my daughter
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