Sensor selection analysis of new non-contact keyboard

Mechanical percussion keyboards are becoming more common in daily life, and the introduction of a new non-contact keyboard has the potential to significantly enhance people’s quality of life. This project aims to develop a smart, contactless keyboard that is both efficient and user-friendly. The design holds great value for future innovations in human-computer interaction.

The system is built around the high-performance MIPS core MCU-PIC32MX460F512L development board, specifically the Cerebot 32MX4 Board from Microchip. This board serves as the central control unit, ensuring reliable and fast processing of input signals. LEDs are chosen as one of the key components due to their low cost, wide application range, and energy efficiency. As light sources, LEDs offer aesthetic appeal and can be used effectively in various environments, including low-light conditions.

Sensor Selection

2.1 Sensor Selection Overview

Photodiodes: These sensors are cost-effective and accurate under normal lighting conditions. However, they fail to function properly in the dark, which limits their use in a keyboard system.

Proximity Sensors: These provide excellent detection capabilities with a longer sensing range. However, they tend to be more expensive, making them less ideal for budget-conscious designs.

Infrared Transceiver Sensors: These allow for effective signal transmission and reception. However, they are relatively costly when paired with LEDs and consume slightly more power than traditional LED-based systems.

Light-Emitting Diodes (LEDs): LEDs are versatile, capable of detecting light within a certain range, and can also serve as illumination sources. They work well in both bright and dark environments, making them a strong candidate for this project.

2.2 Choosing the Right LED

To achieve optimal performance, red LEDs were selected as the sensor. Red LEDs are highly sensitive and can detect movement effectively, although their sensing range is limited. Infrared LEDs have the best light transmission properties, followed by red LEDs in the visible spectrum.

For the LED selection, brightness was a key factor. Higher brightness improves recognition accuracy and provides better illumination. Additionally, the emission pattern should be uniform, with minimal divergence, to ensure consistent performance.

This “white-red” LED is suitable for use as a sensor.

“Red-Red” LED

Preliminary tests showed that “red-red” LEDs are not ideal for this purpose.

3. LED Characteristics

LEDs are known for their low power consumption and high luminous efficiency, using up to 70–80% less energy than fluorescent lamps. Their long lifespan—over 50,000 hours in normal use—makes them highly durable, with only a 30% light decay after that time. They are also environmentally friendly, containing no harmful substances like mercury and emitting no UV or IR radiation, which helps reduce mosquito attraction.

LEDs are eye-friendly due to constant current driving, eliminating flicker issues that can cause eye strain. Their compact size allows for flexible design, and they can be easily combined into modules for larger applications.

The manufacturing process allows for different divergence angles, which affect the spread of light:

(Different LED divergence angles. A smaller angle is preferable for improving detection accuracy.)

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