Design of infrared remote controller decoder using single chip microcomputer

TC9012F is a universal CMOS large-scale integrated circuit for infrared remote control signal transmission, suitable for remote control of TV, VTR, laser player and other equipment. In the market, 9012 infrared remote control with TC9012F as the core is widely used and cheap. The designed 9012 infrared remote control decoder based on AT89C51 microcontroller is applied to the production of real-time display system as an infrared remote control for parameter setting and system control, and has received good results in practical applications.

1 Remote control signal of infrared remote control signal transmitter circuit TC9012F

TC9012F is a 4-bit dedicated microcontroller, and the typical value of the oscillation frequency fosc of its internal oscillation circuit is 455 kHz. When the operation key is not pressed, its internal 455 kHz clock oscillator stops working to reduce battery consumption. The internal frequency division circuit divides the oscillation frequency, fosc, by 12 and converts it into a pulse carrier signal with a frequency of fc=37.9 kHz and a duty cycle of 1/3. The infrared remote control signal transmitter circuit consists of the integrated circuit TC9012F, the keyboard matrix circuit, the driver and the infrared light-emitting diode. The remote control signal is a modulated wave modulated by the remote control coded pulse of the 37.9 kHz pulse carrier, as shown in Figure 1.

The remote control coding pulse consists of the pilot code, user code, function code and the inverse code of the function code. The user code is the same group of codes sent twice, as shown in Figure 2. The user code is 8 bits, so the entire pulse code is 32 bits. The pilot code is a preparation pulse for receiving data. It consists of 8TCP (4.5 ms) of high level and 8TCP (4.5 ms) of low level. The user code and function code are encoded using pulse position modulation (PPM) to distinguish the code value "0" or "1" based on the time interval between pulses. Corresponding to the "0" or "1" of the binary digital signal, the pulse time intervals are 2TCP (1.125 ms) and 4TCP (2.25 ms), respectively, while the width of each pulse remains unchanged, all TCP (0.5626 ms). Since the user code is sent twice and the function code and its inverse code are sent together, the system rarely malfunctions.

This remote controller uses different working modes for the coded pulse of the remote control signal sent for the first time (as shown in Figure 3) and the coded pulse of the remote control signal sent for the second and third times continuously (as shown in Figure 4). In this way, when the button is pressed, starting from the second continuous transmission, only the guide code and the opposite code SO of the first SO of the user code are sent, thereby reducing the receiving processing time and the power consumption of the infrared light-emitting diode. The remote control coded pulse is modulated by the pulse carrier and output by the pin 1 of TC9021F, and then driven by the exciter to drive the infrared light-emitting diode to send out pulse infrared light with a wavelength of 940nm. Assuming that the user code is 76H in hexadecimal, the coded pulse of the remote control signal sent for the first time is shown in Figure 3.

As can be seen from Figures 2 and 3, the output time of the remote control code pulse waveform is 192TCP or 224TCP, and α is the output time of the user code (8 bits). When α≥26TCP, the output time of the remote control code pulse waveform is 224TCP. In addition, for the pulse interval time of the opposite code of the first bit of the user code in the continuously transmitted code pulse, when SO="1", then SO="0", the time is 2TCP, and when SO="0", then SO="1", the time is 4TCP.

2 Decoder Hardware Design

The decoder hardware is based on the AT89C51 microcontroller, as shown in Figure 5. The figure only shows the circuit for receiving infrared remote control signals. After the infrared remote control signal is received by the infrared receiving module, the coded pulse of the remote control signal is demodulated and output from the output terminal A. Its waveform is shown in Figure 3 and Figure 4. This signal is output to the external interrupt INT0 input terminal of AT89C51 through the inverter 74LS04. The microcontroller receives and decodes the coded pulse sent by the infrared remote control TC9021 by running the program.

3. MCU Programming

The main problem solved by the single-chip program is how to decode the signal transmitted by the 9021 infrared remote control. The coded pulse signal is composed of the guide code, user code, and function code. We only analyze the process of obtaining its function code. In the single-chip setting, the internal timer/counter T0 of the single-chip AT89C51 is set to timing mode 1, and the timing time is 1 ms; the external interrupt INT0 is set to the falling edge interrupt trigger mode. Since the coded pulse signal is inverted when receiving, whenever the falling edge of the INT0 external pin signal arrives, the external interrupt INT0 is interrupted, and the timer T0 is started. The timer interrupts each time for 1 ms and is accumulated in the timing counter. When the next external interrupt INT0 is interrupted, the time in the timing counter is read, and the remote control function code is decoded by analyzing the timing time between the two pulses. Figures 6, 7, and 8 respectively give the flowcharts of the decoder main program, the timer T0 interrupt program, and the external interrupt INT0 interrupt program.

4 Conclusion

The real-time production display system is aimed at the production site and conducts quantitative management of production efficiency. It has been widely used in developed countries and some foreign-funded enterprises in China. It can make the production situation clear at a glance and improve production efficiency by real-time displaying the quota task volume, production target and the actual production quantity completed at the current moment. This display system is generally installed above the production line. The staff needs to operate the display system frequently, set and modify the data. The infrared remote control is used to set the parameters of the real-time production display system without contact, which makes the operation flexible and convenient, and has strong anti-interference.