Projection Keyboard is a technology that can be divided into four parts: illumination module, the projection module, sensor module and connectivity module. To be concise, the illumination module projects visible light for users to recognize; the projection module sends out an invisible infrared keyboard to interact with a human finger; the sensor module senses the interaction and conducts a certain program to produce data; the connectivity module is responsible for energy charging and Bluetooth connection.
- In the illumination module, an infrared laser can be divided into gas lasers, solid-state lasers, fiber lasers, photonic crystal lasers, semiconductor lasers, dye lasers, free-electron lasers, and so on. Among these, Helium-neon gas laser is one of the most common ones, which can be used to produce invisible and visible infrared lights. It mainly consists of four parts: laser bore tube, high reflector, glass tube, and output coupler. Inside the laser bore tube, there is Helium-Neon gas mixture with its ratio of atmospheric pressure from 5:1 to 10:1 and its pressure is 133.3 to 266.6 Pa. The mixture causes He-Ne Collision excited helium atoms from the ground state to higher energy excited states. The high reflector functions when a wave reflects back upon itself, gaining more power in each pass. The glass tube creates the environment for the whole process and supports it to happen sustainably and stably. When the radiation builds up continuously and the saturation occurs, output coupler will emit a stable continuous laser beam output ultimately.
- In the sensor module, the main part of this module is the camera which works as a movement sensor. Used to track the finger movement, the image sensor camera contains an anti-aliasing filter to make sure the image is not twisted, two microlenses, color filters, and finally a plane of sensor photosites to sense the captured image. Before entering the image sensor camera, the light shall go through the infrared-pass filter to make sure that only the infrared light projected by the illumination module is sensed by the image camera.
- In the projection module, projection keyboard is used for visualizing the keyboards in the form of visible light. There are two kinds of projection modules, diffractive micro-projector module, and LCD micro-projector module. The two main components of a diffractive micro-projector module are diode laser mount and the diffractive optical element (DOE). Other components of the diffractive micro-projector module are a heat sink and plastic pieces that assemble the components together. As for LCD micro-projector, it contains heat sink, LED, collimator and the lens.
- In the connectivity module, the components that need to be included in the system diagram are not necessarily located inside the shell of the device, unlike the other three modules. This is because the function of the connectivity module is to connect the device to the working environment, power supply and more importantly, the computer where users try to input data. We will not elaborate this module a lot for Bluetooth and USB are two universally used technology and they are not the focus of our team’s research into the technology. We have discussed how the device projects a virtual keyboard to the flat surface in the illustration of projection module.