Takahiro Maeda's Interactive Hand Sensor Allows for Touch-Free Interfaces — Even Through Displays
By firing an infrared beam from under a transparent OLED, this contactless display can pick up your fingers at a distance.
Maker Takahiro Maeda is developing an interactive hand sensor, designed for use with a range of microcontrollers — and capable of picking up motion at a distance of nearly 8" with a reaction time of 1.2 milliseconds.
"The world is full of fast and cheap micro controllers. But it lacks a practical motion sensor," claims Maeda of the inspiration behind his work. "[An] AI camera is not good at depth, it is slow to calculate each time. I want to control [devices] with cleaner and more intuitive movements. I want a sensor that can be easily used by children and people with physical disabilities."
To fill that niche, Maeda has developed what he calls an "Interactive Hand Sensor," designed specifically for contact-free human-machine interaction projects and based on a relatively simple concept: the reflection of light. "The principle is 'Switching Photo Reflector,'" Maeda explains.
"The photo transistor converts the reflected light into current, and the resistor converts it into voltage. When reading the voltage with the AD [Analog-to-Digital] converter, the infrared LED is lit at the SCLK timing of SPI Interface. It is driven for 10 microseconds without a current limiting resistor and emits strong light at a current of about 1.5A."
In doing this, the device acts as a trigger for when an object comes close — though its accuracy for determining distance is poor, Maeda admits, with the trade-off being that it reacts extremely quickly. "The sensor has been tested continuously for more than two years and two months with no problems," he says, with commercial units already on sale in Japan.
To prove the sensor's capabilities, Maeda has created a touchless display programmed in Python — firing the sensor's infrared light through the rear of a transparent OLED screen, allowing users to interact with it without having to physically touch the display. In this project, the sensor is driven by a Raspberry Pi 4 single-board computer — but Maeda has shown it working with devices including the Arduino Nano Every, Raspberry Pi Pico, and Arm's Mbed platform.
More information on the sensor is available on Maeda's Hackaday.io page, and on the project website (in Japanese.)