Kaolid+: A Lid-Type Olfactory Interface for Modulating Sweetness Perception

This repository provides the open-source hardware and software materials for Kaolid+, a lid-type olfactory interface that routes aroma either toward the nose (orthonasal) or through a Y-shaped straw (retronasal) while illuminating the beverage with an RGB light, in order to modulate the perceived sweetness of a drink.

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1. System Overview

Kaolid+ is a cup-lid device, housed in a 3D-printed enclosure, integrating:

• Olfactory unit — a compact piezoelectric air pump pushes air through a scented cotton pad in a scent container; the aroma is routed either toward the nose (orthonasal) or into a Y-shaped straw (retronasal).
• Visual unit — an RGB LED illuminates the beverage from the lid (no-light / orange / blue conditions).
• Control unit — a SparkFun Pro Micro reads a manual switch and drives both the pump (via a transistor and a boost/driver circuit) and the RGB LED.

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2. Repository Structure

kaolid/
├── hardware/
│   ├── cad/            3D models of the lid, cover, scent container
│   ├── electronics/    Schematics, wiring diagrams, BOM
│   └── assembly/       Step-by-step assembly guide
├── firmware/           Arduino sketch (SparkFun Pro Micro) + flashing notes + reproducing the experiment
└── docs/               Figures, photos, supplementary documentation

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3. Hardware

3.1 Main components

Component	Part used in the study	Notes
Air pump	Murata microblower MZB1001T02 (piezoelectric diaphragm)	Driven at 14 V, ~1.6 kPa
Microcontroller	SparkFun Pro Micro 5V / 16 MHz	Reads the switch, drives pump + LED
RGB LED	OptoSupply OSTAMA5B31A (5 mm, common-anode)	8-bit value per channel
Pump driver	Transistor + boost converter	Piezo pump cannot be driven directly by the MCU
Enclosure	3D-printed lid body, cover, scent container	See hardware/cad/
Straw	Custom Y-shaped straw	One branch = beverage, one branch = aroma airflow

3.2 RGB values

The LED is common-anode with the cathodes wired to the PWM pins, so in the firmware a lower analogWrite value is brighter (0 = full on, 255 = off). These are the actual values used to reproduce the colors:

Condition	R	G	B
No light	255	255	255
Orange	30	220	255
Blue	255	255	0

3.3 Folders

• hardware/cad/ — 3D models (editable source (Autodesk Fusion), STL).
• hardware/electronics/ — schematics, wiring, BOM.csv.
• hardware/assembly/ — assembly guide.

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4. Firmware — firmware/

Kaolid+ is controlled by a single Arduino sketch on a SparkFun Pro Micro (5 V / 16 MHz); there is no separate PC application. The microcontroller reads a manual tact switch and locally drives the RGB LED and the air-pump transistor.

Aroma is delivered while the switch is pressed and held during sipping. The piezoelectric pump cannot be driven directly by the MCU, so it runs through a boost/driver circuit at 14 V (~1.6 kPa). The RGB LED is an OptoSupply OSTAMA5B31A 5 mm common-anode LED; the visual condition is selected by uncommenting the matching block in setup() and re-uploading.

4.1 Pin assignment

Pro Micro pin	Function	Note
3	RGB common anode	held HIGH as a pseudo-Vcc
5	Red cathode	330 Ω series resistor
6	Green cathode	680 Ω series resistor
9	Blue cathode	270 Ω series resistor
2	Tact switch	INPUT_PULLUP; LOW = pressed
4	Pump transistor	HIGH = pump on

4.2 Flashing

1. In the Arduino IDE, install Arduino Micro and select Pro Micro (5 V, 16 MHz) with the correct port.
2. Open firmware/src/kaolid_controller.ino, uncomment the desired condition block, and click Upload.
3. Press and hold the switch while sipping to run the pump.

See firmware/README.md for the full RGB value table.

4.3 Reproducing the Experiment

1. Print and assemble the hardware.
2. Flash the firmware.
3. Follow the 8-step preparation in hardware/assembly/assembly-guide.md.
4. Run the six conditions (C1–C6) described in the paper.

Acknowledgments

This work was supported by JST, PRESTO Grant Number JPMJPR21P7, Japan.