Case Study 04 · Electronics / Working Prototype

Acoustic Extinguisher

An autonomous fire extinguisher that runs on sound. It watches for fire on its own, warns the people around it, and puts the fire out with focused pulses of air, with no one needing to be there.

Sensing: IR flame sensor + MLX90614
Control: Arduino Uno
Output: 200 Hz via TPA3116 + 4″ speaker
Build: Fusion 360, 3D printed

The Problem

One needs a person, the other floods the room

Fire is fought in two ways today. Handheld extinguishers are cheap and everywhere, but they only work once someone notices the fire, reaches it, pulls the pin and aims, standing close to it the whole time. A fire in an empty room or in the middle of the night has all the time it needs to grow.

Sprinkler systems act on their own, but only once the heat is high enough to burst the bulb. Then they soak the whole room, along with the electronics, papers and equipment they were meant to protect, and nobody is warned until the water is already falling.

The gap

Protection that watches a space on its own, warns the people nearby and puts the fire out, without needing a person or flooding the room.

Red handheld fire extinguisher in a glass-fronted wall cabinet — Handheld extinguisher: always there, but useless until someone reaches it. Photo: Mibrahim74, CC BY 3.0.

Ceiling-mounted fire sprinkler head with a red glass bulb — Sprinkler head: automatic, but soaks everything in reach. Photo: Brandon Leon, CC BY-SA 2.0.

The Principle

It isn’t the noise. It’s the air.

Diagram: a speaker generates low-frequency sound, oscillating airflow bends and stretches the fire, and the disturbance destabilises combustion

George Mason University students demonstrating a sound-wave fire extinguisher on a pan fire — Precedent: the 2015 George Mason University sound extinguisher. Image © George Mason University.

A speaker pushes air back and forth. Focused through a horn, that oscillating air bends and stretches the fire until combustion can no longer keep up.

Students at George Mason University showed this works in 2015, but someone still had to hold it and aim it. My aim was to make it autonomous: a product that finds the fire, raises the alarm and acts on its own.

Electronics

Detect, confirm, extinguish

Component architecture board: sensing, control, audio output, power and passive components, with the system flow

01
DetectThe IR flame sensor sees the fire; the MLX90614 measures its heat from a distance.
02
ConfirmThe Arduino only fires if both agree: fire seen and more than 6 °C above room temperature.
03
Warn & driveA 200 Hz tone goes through the 12 V TPA3116 amplifier to the 4″ speaker. The deep hum that fights the fire is also an alarm anyone nearby can hear.
04
Repeat3-second blasts, up to three times, stopping once the fire is out.

Circuit schematic: flame sensor and MLX90614 into an Arduino Uno, driving a TPA3116 amplifier and speaker from a 12 V supply — Circuit schematic.

Form Exploration

Physics drew the first sketch

The physics set the core form: a sealed speaker housing, a horn that narrows the air pulses, and a nozzle to aim them. Sketching explored how those pieces sit on a base and where the sensors should look.

Ideation board of horn, housing and stand concepts — Horn, housing and stand explorations.

Identity

Fire is usually fought with force: water, foam and powder, and a person standing in harm’s way. This logo answers with something lighter. A bold, grounded letterform stands firm, a guardian that keeps watch, while three streaks of air stream away from it like pulses leaving the nozzle. Steady at its core, it acts the moment it is needed, so no one has to.

CAD

Eight parts, one printer

Exploded view of the printed parts: enclosure shell, rear plate, horn cone, nozzle tube, sensor yoke, electronics base, bottom panel and cradle

01
Enclosure shellHolds the 4″ speaker.
02
Rear plateSeals the back, with a cable hole.
03
Horn coneNarrows the air pulses.
04
Nozzle tubeAims the pulses at the fire.

06
Sensor yokeClamps under the nozzle and holds the sensors.
09
Electronics baseHouses the Arduino and amplifier.
10
Bottom panelRemovable floor with standoffs.
12
CradleHolds the housing on the box.

Testing

It works

Test 1: a lit match at the nozzle. The device detects it, fires and the fire goes out. Unmute to hear the 200 Hz pulse.

The first full test: no button pressed, no one aiming. The sensors pick up the fire, the Arduino confirms it, and the pulses, loud enough to warn anyone in the room, put it out.

Tests were done on small, controlled fires, with a conventional extinguisher on hand.

Final Prototype

Watches, warns, extinguishes

Side view of the prototype: speaker housing, horn and nozzle above the electronics base, sensor lit green

Front three-quarter view with the sensor cable routed neatly to the base — Sensor cable routed into the base.

Rear three-quarter view showing the sealed speaker housing and power input — Sealed housing and 12 V input at the rear.

It needs no one to operate it, only electricity. It keeps watch, sounds the alarm with its own pulse and puts the fire out, with no water, foam or powder and nothing to refill. That makes it suited to rooms that are often empty or hard to reach: server rooms, labs, kitchens, and even spacecraft.

What's Next

From a match to a room

This prototype handles small fires at close range. The next steps are testing range and fire size, trying lower frequencies and larger drivers, adding a dedicated warning light and alert, and giving the nozzle a way to turn and aim at a fire the sensors find.

The biggest lesson was to test the riskiest part first. Before any sensor or enclosure, I checked the speaker could move enough air to matter, because everything else depended on it.

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