Wireless Data Acquisition System Designed by S3C2410

The functions of handheld terminals are becoming more and more powerful, and the data processing capabilities are becoming stronger and stronger. People's requirements for their wireless communication functions are also getting higher and higher. For this reason, various wireless devices have entered people's lives. On this basis, a large number of wireless devices have entered the field of industrial production. In the industrial or factory floor environment, the use of wireless technology has many advantages; the use of wireless technology can solve the cumbersome difficulties of line layout in industrial production, and can also avoid problems such as corrosion of lines in harsh environments.

1 System Design

Here, the embedded technology is combined with the radio station communication technology to design a wireless data acquisition system. The system is divided into a data acquisition module, a data transmission/receiving module, and a data processing module, as shown in Figure 1. The data acquisition module converts the analog signal obtained by the sensor into a digital signal and then sends it out with a wireless chip. The A/D conversion chip uses MAX132; the data transmission chip uses the wireless transmission/receiving chip IA4421. Use the single-chip microcomputer to configure MAX132 and IA4421 to realize signal acquisition and transmission. The data processing module uses the S3C2410 chip, and the wireless chip IA4421 is configured as a wireless receiving mode. In this way, data acquisition, transmission and processing are realized.



2 Data Acquisition

The data acquisition module uses an A/D conversion chip to convert the received analog signal into a digital signal, and then transmits the digital signal to the data processing module through the data transmission module.

MAX132 is an A/D conversion chip with 18 bits plus 1 sign bit, high precision resolution, and works in serial mode. It can provide a resolution of 2μV in the full range of -512 to +512 mV, and the accuracy can reach ±0.006% of the full scale. The chip has a higher conversion speed than the general integral ADC, up to 100 times per second, and the simple 4-wire serial interface makes it easy to connect with all other microprocessors. In normal working mode, the typical supply current of MAX132 is 60 mA, and only lμA in sleep mode. MAX132 also has 4 programmable digital outputs for external multiplexers or programmable gain amplifiers; there is also an interference suppression circuit with an optional 50 Hz power frequency inside the chip; the chip input current is very small, only 10 pA. MAX132 has the characteristics of high resolution, low power consumption, low price and small size. It can be widely used in remote data acquisition, battery-powered instruments and sensors, signal measurement and industrial process control. The circuit design is shown in Figure 2.


Figure 2 is a typical application circuit diagram of MAX132. Among them, the component values ​​are selected for 16 conversions per second and 60 Hz power frequency interference suppression. Through the 2.5 V high-precision reference source, MAX872 generates a 545 mV reference voltage after voltage division. The voltage signal to be measured is differentially input from the INH1 and INL0 ports; the chip select signal CS, serial data input/output terminal DIN, DOUT, and clock signal Sclk are connected to the microcontroller.

As shown in Figure 3, when the CLK/CONV pin of the IA4421 chip is used to start the conversion, CLK/CONV is high level; if CLK/CONV is set to low level, it will become high level within 10 ms, and a conversion will be performed, and then it will return to idle mode. If CLK/CONV is always at a low level, the conversion will be performed continuously until CLK/CONV becomes a high level again.


3 Data transmission module

3.1 Data transmission module hardware design

The data transmission module uses the IA4421 chip. IA4421 supports direct antenna drive, the design is quite simple and convenient, and the communication distance is long. IA4421 is a fully integrated single-chip low-power, multi-channel FSK transceiver. In the 433 MHz, 868 MHz, and 915 MHz frequency bands that do not require registration, the design fully complies with the relevant regulations of the FCC's ETSI certification. It integrates high-frequency power amplifiers, low-noise amplifiers, I/Q conversion mixers, baseband filters, amplifiers, I/Q demodulators, etc. The required RF is integrated, and only a crystal oscillator and a few decoupling capacitors are required.

3.2 Data transmission module software design

3.2.1 Transmitter function

(1) Send data acquisition instructions, open the acquisition system, and prepare for sending data.

(2) Automatically match the code with the transmitter. The transmitter control software program flow chart is shown in Figure 4. After the microcontroller is powered on and initialized, the configuration of IA4421 is completed. At this time, the chip is configured to transmit mode, then the interrupt is turned on, waiting for data input, receiving the collected signal, and finally sending the information out.



3.2.2 Receiver function

The receiver main program flow is very similar to the transmitter program flow. The flow chart is not drawn here. The receiver function is only introduced as follows: configure the IA4421 chip to receive mode and send the prepared signal; receive data and then transmit it to the processing unit, which is the S3C2410 main chip.

4 Data processing module

The data processing module uses the S3C2410 chip. The S3C2410 processor is Samsung's ARM920T processor core based on ARM's company. It uses a 32-bit microcontroller with a 0.18μm manufacturing process. The processor has independent 16 KB instruction cache and 16 KB data cache, MMU, LCD controller supporting TFT, NAND flash controller, 3-way UART, 4-way DMA, 4-way timer with PWM, I/O port, RTC, 8-way 10-bit ADC, Touch Screen interface, I ² C-BUS interface, IIS-BUS interface, 2 USB hosts, 1 USB device, SD host and MMC interface, 2 SPI. The S3C2410 processor can run at up to 203 MHz.

It adopts embedded Linux operating system, the Linux kernel is stable and the code size is small, easy to cut. The application window system adopts Qt/Embedded system technology. Qt/Embedded is a toolkit for embedded GUI and application development based on Qt. It can run on a variety of embedded devices, mainly on embedded Linux system, and provides Qt standard API for embedded applications. Qt/E, as an implementation tool for embedded GUI, supports frame buffer driver and can directly write frame buffer without X2Servet or X2LIB support, saving memory usage and improving program operation efficiency.

(1) Configure the wireless receiving chip to receive mode, send a receive data command, notify IA4421 to be ready to receive the data, and send a ready signal to notify the sending module to send data.

(2) Perform calculations and analysis on the received data, and then reflect the results on the LCD; the application has an analysis function to analyze the performance of the signal and make an alarm in the event of a signal error.

5 Conclusion

The system uses the MAX132 chip to realize the conversion from analog signal to data signal, and uses IA4421 to realize wireless data transmission. Considering the practicality and flexibility of the system, it can be flexibly wired and is not affected by the physical environment. S3C2410 is used as the main chip of the data processing module.