The Laser pointer is used for computer operation and can be positioned on the fluorescent screen of the display. When the light pen receives the scanning signal on the fluorescent screen, it converts the light pulse into an electric pulse, and the coordinate position of the light pen is calculated by the computer through the control circuit. Inside the laser pointer is a semiconductor laser, which is a kind of LED. An optical lens is usually added to the front to focus. The laser light emitted by the laser pointer is a solid-state laser, and the solid-state laser in the laser pointer is also a laser diode. Most of the current laser pointers are red, and the length that can be indicated is relatively far. Laser pointer is also known as star pointer, handheld laser and so on. It is named because it has a very intuitive visible light beam, which is mostly used for indication. Because of its bright beam and strong resistance to stray light interference, it is now widely used in teaching, scientific research, construction engineering, astronomy and other industries. There are fewer green and blue ones, making it difficult and expensive to make.
A light-shielding plate with a window is added in front of the photoresistor (LDR). When the light scanning electron beam causes the surface of the phosphor screen covered by the LDR to emit light, the resistance value of the LDR decreases sharply, T1 and T2 are turned on, T3 is turned off, and the light-emitting diode D1 is extinguished. Indicates that the light pen points to a character. P1 is used to adjust the sensitivity of the light pointer.
Laser modulation-demodulation circuit
The easy way to transmit audio signals is amplitude modulation plus pulse width modulation. In the picture you can see a laser-based amplitude modulation-pulse width modulation circuit, which is designed by Ron (K7RJ), the purpose is to use as simple as possible off-the-shelf parts plus a Green laser pointer to transmit sound. This circuit contains an optical receiver based on a photodiode. However, since the main purpose of the circuit is to demonstrate the modulation circuit, and there is no effort on sensitivity and no focusing lens, the communication distance is very short, only about 100 meters.