Signal---Infrared in an intelligent control system

　　

Huaqing Vision Lecturer

We know that human eyes can see the visible light by wavelength from long to short arrangement, followed by red, orange, yellow, green, green, blue, purple. The wavelength range of the red light is 0.62~0.76μm; The violet wavelength range is 0.38~0.46μm. The light that is shorter than the violet wavelength is called ultraviolet light, which is longer than the red wavelength is called infrared ray, see Figure 1. Infrared remote control is the use of the wavelength of the 0.76~1.5μm between the near infrared to transmit the signal.

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Infrared remote Control system

Commonly used infrared remote control system generally sub-transmit and receive two parts. The main component of the transmitting part is the infrared light emitting diode. It is actually a special light emitting diode, because its internal material is different from the ordinary light-emitting diode, so when a certain voltage is applied at both ends, it emits infrared rather than visible light. At present, the infrared light emitting diode emitted by a large number of infrared wavelength is about 940nm, the shape of the same as the ordinary light-emitting diodes (see Figure 2), but the color is different. Infrared light emitting diodes generally have black, dark blue, transparent three kinds of colors. The method of judging the infrared light-emitting diode is the same as the ordinary diode: using a multimeter to block the amount of infrared light-emitting diode positive and reverse resistance can be.

　　

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The receiving part of the infrared receiver tube is a photosensitive diode. In the actual application to the infrared receiving diode plus reverse bias, it can work normally, that is, the infrared receiver diode in the circuit is applied in reverse, so as to obtain a higher sensitivity. Infrared receiving diodes generally have round and square two.

Since the emission power of infrared LEDs is generally small (100mW or so), so the signal received by the infrared diode is relatively weak, so it is necessary to increase the high-gain amplification circuit. In the previous years, commonly used μpc1373h, cx20106a and other infrared receiving special amplification circuit. In recent years, whether it is amateur production or formal products, most of them use the finished infrared receiver head. The package of the finished infrared receiver has two kinds: one is the metal shielding, the other is the plastic package. All have three pins, i.e. power supply positive (VDD), power supply negative (GND), and data output (VO or out). Figure 3 shows the shape of some of the finished IR receiver heads. The pin arrangement of the infrared receiving head varies depending on the model, and can be referenced by the manufacturer's instruction. The advantage of the finished infrared receiver is that it does not require complex debugging and shell shielding, which is very convenient to use as a transistor. However, pay attention to the carrier frequency of the finished infrared receiver head when using. The usual carrier frequency for infrared remote control is 38kHz, which is determined by the 455kHz crystal oscillator used by the transmitter. On the transmitter side to the Crystal Oscillator integer division, the frequency division coefficient is generally taken 12, so 455khz÷12≈37.9 khz≈38khz. There are also some remote control system using 36KHZ, 40kHz, 56kHz, etc., generally by the transmitter end crystal oscillator frequency to determine.

　　

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Infrared remote control is characterized by not affecting the surrounding environment, do not interfere with other electrical equipment. Because of its inability to penetrate the walls, so different rooms of household appliances can use a universal remote control without interference; The circuit debugging is simple, as long as the given circuit is connected to the correct, generally do not need any debugging can be put into work; easy to encode and decode.

Because of the production of a large number of manufacturers of infrared remote control ASIC, when needed retrace can. Therefore, the infrared remote control in household appliances, indoor near-distance (10 meters) remote control has been widely used.

Infrared remote control system with multi-channel controlling

The infrared emitting part of multi-channel control usually has many keys, which represent different control functions. When a key is pressed on the transmitter side, there is a different output state at the receiving end accordingly. The output state of the receiver can be divided into five forms: pulse, level, self-lock, interlock, data. "Pulse" output is when pressing the transmitter side button, the receiving end of the corresponding output output a "valid pulse", the width is generally around 100ms. "Level" output refers to the transmitter side when the key is pressed, the receiving end of the output output "active level", the transmitter release when the key, the receiver "effective level" disappears. The "Effective pulse" and "active level" here may be high or low, depending on the static state of the corresponding output foot, such as low at Static, "high" is valid, if the static is high, then "low" is valid. In most cases "high" is valid. "Self-locking" output refers to the transmitter side each time a key, the receiving end of the corresponding output to change the state, that is, the original high level to low level, the original low to high level. This type of output is suitable for use as power switch, mute control, etc. This output is sometimes referred to as "inverting". The "interlock" output means that multiple outputs are purged from each other and only one output is valid at the same time. The selection of television sets is the case, other such as dimming, speed, audio input selection. "Data" output refers to the number of transmission keys, the use of several outputs on the receiving end to form a binary number, to represent the different key input. In general, the receiver in addition to a few data output, there should be a "data valid" output, so that the latter level of timely access to data. This type of output is generally used to interface with a single chip microcomputer or computer.

In addition to the above output form, there are "latch" and "staging" two forms. The so-called "latch" output refers to the transmitting end of each signal, the receiver output is "stored" until a new signal is received; " The staging output is similar to the level output described above.

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Signal---Infrared in an intelligent control system