Design principle of infrared circuit of single chip microcomputer

TV 、 The air conditioner can't live without the infrared remote control . The air conditioner remote control is actually an infrared signal transmitting device , The air conditioner body has an infrared receiving probe , It can receive the infrared signal sent by the remote control and analyze , So as to realize the function of remote control , The same principle applies to TV remote control . Now there are many mobile phones with infrared function , By matching the communication protocol , It can realize the function of mobile phone remote control TV and air conditioner . Pass below Hardware and Software Two aspects to share with you , The principle of infrared remote control .

This part includes , Principle of infrared emission part 、 Principle of infrared receiving part as well as The principle of software coding .

1 Circuit principle of infrared emission part

The infrared emission function mainly consists of Infrared emission tube To achieve , The infrared emitting tube is and transparent in appearance LED Light emitting diodes are very similar , Its driving and control modes are also the same . When using single chip microcomputer to control the transmitting tube , Generally, triode is used to drive ,NPN Triode and PNP Triode can achieve . Use it as shown in the figure below PNP Triode .

PNP The base of the triode is connected to the single chip microcomputer through resistance GPIO mouth , The transmitting tube is connected to... Through a current limiting resistor PNP On the emitter of the triode . When the microcontroller's GPIO Output high level PNP The triode is in the cut-off state, and the infrared emitter does not work ; When GPIO Output low level PNP The triode turns on and the emitter works , Emit infrared rays invisible to the naked eye , Received by the receiving tube . Each key on the remote control has a certain code , This coding is actually a high-level and low-level pulse that follows certain rules , The receiving circuit parses the pulse to perform the corresponding operation .

2 Circuit principle of infrared receiving part

remember , Infrared emission and infrared reception are a pair , Use in pairs . The launch tube is white , The receiving tube is black . You can use a triode to build a receiving circuit or a comparator to build a circuit , The following shows the circuit of infrared receiving with triode circuit . As shown in the figure below .

  When no infrared signal is received , The receiving pipe is not conductive , triode Q1 No conduction , triode Q3 No conduction , The MCU receives a continuous high level ; When the receiving tube receives the infrared signal , MCU receives low level signal . When the key on the remote control is pressed , The coding pulse corresponding to the key will be received by the single chip microcomputer , The single chip microcomputer analyzes the pulse , You can know which key on the remote control is pressed , So as to realize the user's operation .

however , The anti-interference ability of black infrared receiving tube is relatively low , When designing the circuit, generally do not choose , Instead, use a special infrared receiver , The most commonly used model is HS0038. and , Its infrared receiving circuit is simple , Strong anti-interference ability .

 3 Infrared software code analysis

The pulse coding mentioned above is the communication content between infrared emission and infrared reception , Data or content of communication , It is called communication protocol . Generally speaking , Infrared communication follows NEC Coding protocol specification .

NEC According to the agreement , The working frequency is 38KHz, Its data format consists of the following parts ： Pilot code 、 User code 、 User code complement 、 Key code 、 Key code complement, etc . A complete key / The data cycle is 108ms.NEC Coding rules 0 and 1 The code of is as follows ：

code 0：0.56ms High level +0.565ms Low level =1.125ms

code 1：0.56ms High level +1.685ms Low level =2.245ms, As shown in the figure below .

  When a key on the remote control is pressed , The transmitting tube will send out a string containing the pilot code 、 User code 、 User code complement 、 Key code 、 The pulse of key code complement comes out , If you want to translate the pulse , Just look at 0 and 1 Sequence , The length is 2.245ms The pulse of represents data 1, Pulse length is 1.125 The pulse of represents data 0. Similar pulse data are shown in the figure below .

The infrared special probe at the receiving end should sense some pulses and send them to the single chip microcomputer , Single chip microcomputer analyzes pulse data , Calculate the user's key information , Then execute the corresponding commands and logic , In this way, users can remotely control the air conditioner and TV on the sofa .

Nowadays, many mobile phones have integrated infrared emission circuits , It also has a self-learning function, which allows the mobile phone to match the coding protocol of the device according to the operating instructions , After the protocol is matched, you can remotely control the TV through your mobile phone 、 Air conditioning and other equipment , At this time, the mobile phone becomes a remote control .

Because the communication part has to deal with complex data , So this kind of circuit needs the support of MCU .

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