Design of Multifunctional Infrared Remote Control

1. Introduction

At present, people's material and cultural living standards are improving day by day, and various household appliances have entered thousands of households. Among them, most household appliances have their own remote controls. People often look for the corresponding remote control everywhere to control a certain appliance, which brings a lot of inconvenience to people's lives. In order to solve this problem, this paper proposes a design scheme of a multi-functional remote control: the remote control can have the remote control function of multiple appliances through self-learning, which saves time and effort, so that people can avoid the trouble of facing many remote controls at the same time.

2. Function

1. Applicable to coded infrared remote control household appliances;

2. Can remotely control multiple household appliances;

3. It has a learning / control multiplexing key, 5~10 device selection keys, and 10~20 function control keys. One device selection key and each function control key can be used together to control one device.

Figure 1 Structural diagram of a multifunctional infrared remote control

4. The common functions of multiple devices can be learned and controlled through a device selection key and various function control keys;

5. Low cost and strong anti-interference ability.

3. Principle

Figure 1 shows the block diagram of the multifunctional infrared remote control. The remote control consists of infrared receiving and transmitting circuits, signal conditioning circuits, central controller 8031 , program and data storage, keyboard and status indication circuits.

The remote control has two states: learning state and control state. When the remote control is in the learning state, every time the user presses a control key, the infrared receiving circuit starts to receive external infrared signals and converts them into electrical signals. After detection, shaping, and amplification, the CPU samples them regularly and stores the binary data of each sampling point in units of 8 bits into the designated storage unit for future use in controlling the device. When the remote control is in the control state, every time the user presses a control key, the CPU reads a series of binary data from the designated storage unit and outputs them serially (the time interval between bits is equal to the time interval during sampling) to the signal holding circuit. At the same time, the modulation circuit modulates the signal, amplifies the modulated signal, and transmits it by the infrared emitting diode, thereby realizing the control of the device function corresponding to the key. [page]

4. Design of some circuits

1. Infrared receiving circuit

As shown in Figure 2 , press the learning / control key to switch the CPU to the learning state. At this time, the learning state indicator D5 lights up (see Figure 4 ). When a device selection key is pressed, the program adjusts the data pointer (set by the program developer) to point to the starting unit of a data area of ​​a specified length in the data memory . When a control key of the remote controller and a control key of the remote controller being learned are pressed at the same time, the 8031 ​​will output a low level to the P3.1 pin (i.e., the JR end) under program control (the original initialization program sets it to a high level), see Figure 4. The level signal at the JR end is the control level of the NOR gate U1A . When P3.1=0 , U1A outputs the inverted signal of the input end. That is, the infrared receiving circuit composed of D1 and U4 is responsible for receiving the signal sent by the remote control to be learned. When D1 has an infrared signal input, the signal is demodulated, shaped, and amplified by U4 (the decoded pulse is in reverse phase with the original encoded pulse) and output from pin 7. It is reversed through the NOR gate U1A and input to the P1.4 pin of 8031 ​​through the IN pin , as shown in Figure 2. The first high-level pulse of this signal quickly charges C4 (reasonably select the parameters of R3 and R4 to prevent repeated triggering), and at the same time sends a falling edge signal to the INT1 pin of 8031 ​​through the IT pin of U2A . After the CPU responds to the interrupt, the IN infrared encoding signal of U1A is collected from P14 regularly to form a series of binary digits, and stored in the data area of ​​the designated device and the designated key in units of 8 bits (error checking can be performed through continuous transmission of one code), thereby completing the learning of a key. If you want to learn the functions of other keys, the method is the same. If you want to learn the functions of each key of another device, press another device selection key of this remote control, and then press each function control key respectively to learn the functions of the remote control being learned. [page]

2. Infrared transmitting circuit

As shown in Figure 3 , press the learning / control key to switch the CPU to the control state, and the control state indicator D6 lights up (see Figure 4 ). At this time, press a device selection key, the system will be in the control state of a certain device. When a function control key is pressed again, the system uses the device number and function key number to address, find the data storage area address of the corresponding function key of the corresponding device (these data are collected point by point when learning the key function), read out these data in sequence, and control the CPU to output them to the OUT pin of the modulation circuit U2B in bit units through the P1.5 pin (the time interval is the same as the sampling time interval) . After modulation by the modulation circuit composed of U2B , U2C , C5 , R7 , and R8 (the modulation frequency is 38KHZ ), it is amplified by Q1 and drives D4 to output infrared remote control signals to achieve control of a function of the selected device.

3. Overview of other circuits

See Figure 4. This part of the circuit includes learning and control indication circuit, data and program storage circuit, keyboard circuit, etc. The learning and control indication circuit uses light-emitting diodes for indication, and the control signals are output by the P1.6 and P1.7 pins of 8031 , and then drive D5 and D6 for indication respectively through the amplifier circuit; the device number display circuit uses a single-digit digital tube static display; the keyboard circuit uses an inquiry scanning keyboard; the program memory uses common ROM or EEPROM , and the data memory can use a relatively low-cost random electrical erasable memory compatible with 6264 or 62128 .

V. Conclusion

This design is only applicable to code division infrared remote control devices, and does not involve frequency division infrared remote control devices and infrared remote control devices with FM signals other than 38kHz . If you want to expand these functions of the remote control, just add a frequency measurement circuit to the infrared receiving circuit and use a CNC signal generator as a modulation circuit in the infrared transmitting circuit.

References

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