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Infrared remote control is not very effective due to the influence of remote control distance and angle. If using frequency modulation or amplitude modulation to transmit and receive codes, the remote control distance can be increased without angle influence. The infrared remote control transmitting module and the receiving module can be used in indoor infrared remote control, it does not affect the surrounding environment and does not interfere with other electrical equipment. Because it cannot penetrate the wall, household appliances in different rooms can use universal remote control without mutual interference; the circuit debugging is simple, as long as the given circuit is connected correctly, it can be put into work without any debugging generally; coding and decoding are easy , Multi-channel remote control is possible. Now infrared remote control has been widely used in household appliances and indoor short-distance remote control. In addition, the module can also be used in other infrared remote control systems, and the application prospect is very broad.

1. The characteristics of infrared light: The visible light that human eyes can see is red, orange, yellow, green, cyan, blue, and purple in order (from longest to shortest) according to wavelength. The wavelength range of red light is 0.62μm～0.76 μm, light with a wavelength longer than red light is called infrared. Infrared remote controllers use near-infrared rays with a wavelength between 0.76μm and 1.5μm to transmit control signals. The characteristic of infrared is that it does not interfere with the work of other electrical equipment, nor does it affect the surrounding environment. The circuit debugging is simple, if the transmitting signal is coded, multi-channel infrared remote control function can be realized.

2. Infrared emission and reception The infrared remote control system that people see is divided into two parts: emission and reception. The emitting element of the emitting part is an infrared light-emitting diode, which emits infrared instead of visible light. The infrared wavelength of the commonly used infrared light-emitting diode is about 940nm. The shape is the same as that of the ordinary quasi 5mm light-emitting diode, but the color is different. Generally there are three types: transparent, black and dark blue. Judging the quality of infrared light-emitting diodes is the same as judging ordinary diodes. The emission power of a single infrared LED is about 100mW. The luminous efficiency of infrared light-emitting diodes needs to be measured with a special instrument, and under amateur conditions, it can only be roughly judged by the draw distance method based on experience. The infrared receiving tube of the receiving circuit is a kind of photosensitive diode. When in use, the infrared receiving diode must be reversely biased so that it can work normally and obtain high sensitivity. Infrared receiving diodes generally have two types: round and square. Since the transmitting power of the infrared light-emitting diode is relatively small and the signal received by the infrared receiving diode is weak, a high-gain amplifier circuit must be added at the receiving end. However, nowadays, whether it is an amateur production or a formal product, the integrated receiver of the finished product is mostly used. The integrated infrared receiver is a module that integrates infrared receiving, amplification, filtering and comparator output, with stable and reliable performance. Therefore, with the integrated receiving head, people no longer make a receiving amplifier circuit, so that the infrared receiving circuit is not only simple but also highly reliable.

Two commonly used shapes of infrared receivers have three pins, namely power supply positive VDD, power supply negative (GND) and data output (Out). The pin arrangement of the receiving head varies from model to model. Figure 3 lists the differences in the pins due to the different shapes of the receiving head. The main parameters of the infrared receiver are as follows: Working voltage: 4.8～5.3V Working current: 1.7～2.7mA Receiving frequency: 38kHz Peak wavelength: 980nm Static output: high level output low level: ≤0.4V output high level: close Operating Voltage

3. Infrared remote control transmitter circuit

The block diagram of the infrared remote control transmitting circuit is the functional composition of all the current infrared remote control transmitting circuits. The encoder is the modulation signal. The encoding method according to the purpose of the remote control can be very simple or very complicated. For example, the encoders used for remote control transmission of TV, VCD, DVD and audio system have more than 50 kinds of control functions. At this time, the encoders adopt special infrared coding protocol for strict programming, but the control function The encoder of the infrared remote control is simple and flexible. The former encoder is encoded by the professionals of the manufacturer according to the infrared remote control protocol, while the latter is suitable for general electronic technicians and electronic hobbyists. The 38kHz oscillator in Figure 4 is a relatively simple carrier signal, but there are differences between professional and amateur ones. The professional oscillator uses a crystal oscillator, while the latter is generally an RC oscillator. For example, the transmitter on the infrared remote control of a color TV uses a 455kHz crystal oscillator, which is divided by integer frequency, and the frequency division factor is 12, that is, 455kHz÷12=37.9kHz. Of course, there are also some industrial remote control systems that use carrier signals such as 36kHz, 40kHz, or 56kHz.

Because the control distance of the infrared remote control is about 10 meters, to reach this index, the carrier frequency (38kHz) of its emission is required to be very stable. The non-professional RC (38kHz) carrier frequency has poor stability, often deviating from 38kHz or even far. This greatly shortens the control distance of the remote control. Because the crystal oscillator frequency is very stable, the remote controllers of professional manufacturers all use the crystal oscillator's 38kHz as the remote control carrier to send signals.