I. Abstract
The negative impacts of existing mechanical keystroke keyboards on people's lives are gradually becoming apparent. New contactless keyboards, on the other hand, can improve people's quality of life. Therefore, the development of such keyboards is of considerable value.
This design uses the Microchip PIC32MX460F512L high-performance MIPS core MCU—the Cerebot32MX4Board—as the main control board, and employs LEDs as one of the core components due to their inexpensive nature and wide range of applications. LEDs serve as both sensing devices and light sources, offering numerous practical and commercial advantages such as aesthetics and a professional appearance. Therefore, this project was designed.
Selection of two sensors
2.1 Selection of Several Sensors
① Photodiode
It features low price and high accuracy. However, it lacks recognition capabilities at night.
This sensor is inexpensive and highly sensitive to ambient light. It requires light to function. However, it is ineffective as a keyboard sensor in low-light conditions.
③ Proximity sensor
This sensor has excellent recognition capabilities and a long sensing distance. However, it is relatively expensive, resulting in higher costs.
④ Infrared transceiver integrated sensor
This sensor element integrates transmitting and receiving for convenience. However, it is relatively more expensive than LEDs, and its power consumption is also slightly higher.
⑤ Light Emitting Diode (LED)
This device can sense light and has the ability to identify objects within a certain distance, making it suitable for use on keyboards. It also has an luminous effect, providing some illumination in the dark.
2.2 Selection of Light Emitting Diodes
To achieve the desired effect, a light-emitting diode (LED) is selected as the sensor. Red LEDs are preferred, as while LEDs can sense light, their range is short. Based on the characteristics of light energy and reflection, infrared light transmits energy best; therefore, in the visible light band, red LEDs are the first choice.
When selecting LEDs, consider brightness: choose those with higher brightness for better identification and illumination. Also consider emission uniformity: select red LEDs with concentrated emission rather than excessive dispersion.
Regarding "white hair and red hair"
This type of "white-to-red" light-emitting diode is suitable for use as a sensor.
Regarding "red hair red"
Preliminary testing indicates that this type of "red-emitting" LED is not suitable as a sensor.
3. Characteristics of Light Emitting Diodes
The lamps have low power consumption and high luminous efficacy, saving approximately 70% to 80% of electricity compared to fluorescent lamps;
Long lifespan: Under normal use, the lifespan exceeds 5,000 hours, and under ideal conditions, it can even reach more than 100,000 hours, which is equivalent to a year of continuous lighting. Moreover, the performance is stable, and the light decay is only 30% after 50,000 hours. Environmentally friendly: It does not contain harmful substances such as mercury, is recyclable and reusable, and has no infrared or ultraviolet radiation (therefore, it can avoid attracting mosquitoes).
High eye comfort: Due to constant current drive, there is no flicker problem, which can protect the eyes well; Flexible size, individual, small size, can be freely combined to form light-emitting modules.
Different manufacturing designs of light-emitting diodes (LEDs) result in different divergence angles. For example:
(The type of divergence angle of the LED. It is best to choose one with a smaller divergence angle, as this will improve the accuracy of the identification.)
