index
1. What is infrared
The human eye can see visible light by wavelength from long to short order, followed by red, orange, yellow, green, cyan, blue, purple. Wherein the red wavelength range of 0.62 0.76μm ~; violet wavelength range of 0.38 ~ 0.46μm. Violet wavelength shorter than ultraviolet light is called, the wavelength longer than red, the light is infrared. Infrared remote control is a wavelength of the near infrared between 0.76 ~ 1.5μm to transmit a control signal.
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Composition II. Infrared System
Infrared remote control has been widely used in various types of household electrical appliances, it appears to use electrical appliances to provide a lot of convenience. Infrared systems are generally composed of two major infrared transmitting device and an infrared receiving equipment. Infrared emitting circuit means in turn a keyboard, infrared code chip, and the infrared emission power supply circuit. IR receiving apparatus may be an infrared receiver circuit, infrared decoder chip, the power supply circuit and the application. Usually better to allow a signal to be transmitted sends out will often binary data signal a pulse modulated signal emitted by the infrared emission control. Commonly used with a pulse width modulation (PWM) signal modulation is achieved by pulse width modulation, and when the pulse signal is achieved by the time interval between the burst modulation (PPM) in two ways.
III. Infrared emission control
Infrared remote control transmitting device, which is usually we say that the infrared remote control circuit is composed of a keyboard, infrared encoding circuit, a power supply circuit, and an infrared transmitter circuit. The main element is an infrared emitting infrared light emitting diode circuit. It is actually a special light emitting diode; inner material due to its different from ordinary light emitting diodes, so when applying a constant voltage across it, it will not emit visible light is infrared light. Currently infrared wavelength infrared light emitting diodes emits a lot of use is about 940nm, the light emitting diode φ5 general shape and the same.
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IV. Infrared remote control transmitter
Typically infrared remote control and to improve performance by reducing power consumption, conventional infrared remote control transmission carrier wave binary-coded manner, a carrier frequency of 38kHz is used, which is a 455kHz oscillator transmitter used to decide. To the transmitting end of the crystal oscillator integer divide, generally the frequency dividing factor 12, so 455kHz ÷ 12≈37.9kHz≈38kHz. There are also remote control system using 36kHz, 40 kHz, 56 kHz, etc., it is generally determined by the oscillation frequency of the transmitter crystal. Therefore, a general infrared remote control is a remote control signal (binary pulse code) modulated on a 38KHz carrier, after the buffer amplifier to the infrared light emitting diode, the conversion of an infrared signal emitted.
There are several binary pulse code, which is most commonly used PWM code (Pulse Width Modulation Code) code and PPM (pulse position modulation between the time code to achieve burst interval signal modulation). If you are developing the infrared receiver device, be sure to know the encoding and carrier frequency infrared remote control, we can choose to develop integrated infrared receiver and decoding scheme.
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V. infrared receiver
IR infrared receiving device is a receiver circuit, decoding the infrared, the power supply circuit and the application. The main role of the infrared remote receiver is sent to the remote transmitter channel improved infrared light into an electrical signal, and then amplification, limiting, detection, shaping, forming the remote command pulses output to the remote microprocessor. In recent years, both amateur production or a formal product, are used mostly finished infrared receiver. Infrared receiver finished package substantially two: one using metal masking; one is the plastic package. It has three pins, i.e., a positive power supply (the VDD), a negative power source (GND) and a data output (VOUT). Note that when finished using the received first infrared carrier frequency, waveform and additionally in the remote control code receiver chip output terminal received waveform.
VI. Data Format
Data format includes a preamble, a user code, data code and data code inverted, accounting for the total 32-bit encoding. Encoded data is inverted data inverted code can be used for error correction coding of the data. Note: the user code of the second paragraph may also be arranged to the inverted first segment of code in the remote user application circuit.
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VII. Bit Definitions
User data code or codes each bit may be bit '1', it may be a bit '0'. Distinguish between '0' and '1' using pulse time interval to distinguish, this coding method is called pulse position modulation mode, the English abbreviation PPM
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