Prototype 1 — the €87 proof of concept

Status: parts ordered · July 2026 · next update when the box arrives

Prototype 1 exists to answer one question: is quiet, distance-coded vibration on your head actually useful and comfortable? Not "can electronics measure distance" — they can — but whether the interaction works for a human on a walk. Everything about this build is optimised for answering that fast and cheap.

Concept mockup: black baseball cap on a mannequin head with a small ultrasonic distance sensor mounted on the brim, a thin cable routed along the cap seam. — AI-generated concept mockup of the cap-mounted sensor — not a photo of the real prototype. Real build photos will replace these as the project progresses.

What's in it

Part	Role	Cost
Arduino UNO R4 Minima	The brain	€19.99
Grove Base Shield V2	Plug-in wiring — no soldering anywhere	€4.11
Grove VL53L0X laser distance sensor	Indoor test sensor (~2 m)	€8.83
Grove vibration motor	The tap on the head	€2.46
DFRobot A02YYUW waterproof ultrasonic	Outdoor primary sensor	€20.90
JSN-SR04T waterproof ultrasonic	Outdoor baseline / spare	€19.51
Power bank, cables, jumpers	Power and plumbing	~€35
Baseball cap, Velcro, foam tape	The hat part of The Hat Project	~€10

Why two outdoor sensors? Bright sunlight blinds cheap laser (ToF) sensors — one of the clearest findings in the research — so outdoors the plan is ultrasonic, which doesn't care about light at all. The two ultrasonic probes get A/B tested against each other.

How the warning works

Zone	Distance	What you feel
Clear	beyond 1.8 m	Nothing. Silence is the default.
Far	1.2–1.8 m	A soft pulse every second or so
Medium	0.7–1.2 m	Pulses twice a second
Near	0.35–0.7 m	Quick, insistent pulses
Danger	under 0.35 m	Rapid buzzing — look up now

The firmware is deliberately paranoid about false alarms: readings are median-filtered and an obstacle must be confirmed by three consecutive readings before the motor is allowed to speak. False alerts killed every comparable product on the market — this project treats them as the primary enemy from day one.

The seven questions Prototype 1 must answer

Can I distinguish several proximity levels through vibration alone?
Is the vibration noticeable but not annoying over 20+ minutes of walking?
Is the response fast enough at slow walking speed?
Does it work in woodland shade — and how badly does direct sun degrade it?
Can it detect thin branches, or only broad obstacles?
Does head movement cause missed detections or false alarms?
What warning distances feel natural?

The test plan

Desk first, cap second, trail last: bench tests against cardboard and wooden dowels (nobody has ever published data on whether these sensors can see a 2 cm twig — those tests will be original data), then a headband comfort trial, then an indoor obstacle course of towels and pool noodles, then a safe outdoor area with a sighted friend. Every session ends with a logged result. The full protocol, firmware code included, lives in the project's open documentation.

What it will look like

These are AI-generated concept mockups based on the actual parts list — useful for imagining the build, but honesty first: none of these are photos of a real device yet. When the parts arrive and the prototype exists, real photos replace these renders, warts and all.

Concept mockup of the bench build: Arduino UNO with a Grove base shield, plug-in sensor and vibration motor modules, a power bank, and a black cap with Velcro strips on a wooden desk. — The desk-test setup: UNO R4, Grove shield, plug-in modules — no soldering anywhere. (Concept render)

Concept mockup close-up of a small ultrasonic sensor mounted on a cap brim, angled 15 degrees upward. — The brim mount, angled 10–15° up — aimed where branches live. (Concept render)

Concept mockup of the open cap showing the vibration motor pocket in the sweatband and a small pouch holding the controller board and power bank. — Inside: motor against the sweatband, brains and battery in a pouch. (Concept render)

Concept mockup rear view of the cap showing the cable routed along the seam with slack, running down toward a backpack. — Cable routed with slack — it must pull free if snagged, never loop the neck. (Concept render)

Concept mockup of a maker-grade prototype on a hiker: sensor module velcroed to a cap, wires taped along the side, Arduino and power bank in an open backpack pouch. — The honest version: Velcro, tape, and an Arduino in a backpack. Prototype 1 will look like this, not like a product. (Concept render)

Real build photos and test logs will appear here as they happen. The blog carries the running story.