Design of embedded wireless real-time image transmission system with ARM processor S3C2440A as the core

1 Introduction

With the development of informatization, intelligence, and networking, embedded system technology will also gain broad development space. In the 1990s, embedded technology was in full swing and has now become a common development direction for communications and consumer products. In the field of communications, digital technology is completely replacing analog technology. There is no doubt that analog image acquisition systems will be replaced by digital image acquisition systems. Among them, embedded image acquisition systems have attracted more and more attention due to their superior performance. At the same time, in the context of technological advancement that promotes increasingly wireless information transmission, wireless image transmission has become the forefront of image transmission. For remote and mobile systems, the way wireless network access transmits data is very important. This article introduces a wireless image transmission system using nRF2401 as a transmission method. The system consists of two parts: a wireless camera and a picture receiver, and has the functions of video image collection, compression, transmission and storage.

2 Overall system design plan

The entire image transmission system includes two parts: a wireless camera and a picture receiver. The wireless camera is mainly composed of a CMOS camera, JPEG compression coding and wireless transmission part. The image acquisition part uses an embedded processor to control the CMOS camera to collect image data and perform JPEG compression, and then uses nRF2401 to transmit the processed image information. After the picture receiver receives the picture information, it stores the picture file in the hard disk through the software and displays it on the LCD. The structure of the entire wireless real-time image transmission system is shown in Figure 1.

Figure 1 Structure diagram of wireless real-time image transmission system

3 Design of wireless camera

The wireless camera designed in this article uses an embedded system based on the Linux 2.6 kernel [1], which excellently completes the functions of image collection, compression and wireless transmission.

3.1 Hardware design

The embedded wireless camera consists of a CMOS camera, USB2.0 controller CY7C68013A, nRF2401 transmitting part, and S3C2440A embedded system, as shown in Figure 2.

Figure 2 Hardware structure of embedded wireless camera system.

3.1.1 CMOS camera

The CMOS camera used in the system is Mesh 2000B produced by Mesh Company. It uses the OV511+7260 camera solution. Due to the drivers of these two chips in the Linux 2.6 source code, it brings great convenience to our design. The camera has a video resolution of 640 (horizontal) x 480 (vertical) pixels, and the clarity can meet most applications. It also has good power management functions, complete automatic brightness, white balance control, and provides color saturation , contrast, edge enhancement, gamma table and other advanced digital image control functions.

3.1.2 Wireless transceiver chip nRF2401

The nRF2401 chip, like the Bluetooth chip, both works in the 2.4GHz free frequency band and has 125 channels, which can meet multi-frequency and frequency hopping needs. Frequency hopping communication has the characteristics of strong anti-interference ability and good security and confidentiality. The spectrum density of the frequency hopping signal is low and it is submerged in the noise. In addition, the confidentiality of the frequency hopping code makes it difficult to be eavesdropped and deciphered. nRF2401 supports multi-point communication, the maximum transmission rate exceeds 1Mbit/s, and has a higher transmission speed than Bluetooth. It is designed using the SoC method and requires only a small number of peripheral components to form a radio frequency transceiver circuit. Unlike Bluetooth, nRF2401 does not have a complex communication protocol. It is completely transparent to users, and products of the same type can communicate freely. What's more, the nRF2401 is cheaper than Bluetooth products. Therefore, nRF2401 is the industry's low-cost radio frequency system-on-chip with smaller size, less power consumption, and the fewest peripheral components.

3.1.3 USB2.0 controller CY7C68013A

The USB2.0 controller CY7C68013A launched by CYPRESS is a complete solution for USB2.0. It is not only responsible for USB transaction processing but also has the control function of the microprocessor, and can also be used as the main control chip of the USB external chip. The chip includes a high-speed 8051 microcontroller with 8KB on-chip RAM, 4KB FIFO memory, general programmable interface (GPIF), serial interface engine (SIE) and USB2.0 transceiver, 6 programmable control output lines, 9 address outputs Lines and 6 universal destination preparation input lines; the data line width can be 8 bits or 16 bits. Its small size and high cost performance make the chip suitable for various USB devices such as mass storage, printers, scanners and PCMCIA. Has been widely used.

3.1.4 Embedded processor S3C2440A

Since the image compression used in this system is software compression, when selecting an embedded processor, it is necessary to measure whether the processor's performance is capable of JPEG compression procedures and USB data transmission. In this system, the embedded processor adopts the 16/32-bit RISC embedded microprocessor S3C2440A based on the ARM920T core of Samsung Company of South Korea. The main frequency is up to 400MHz. It is suitable for image and video processing and is mainly aimed at high cost performance and low power consumption. application. S3C2440 has rich built-in peripheral resources, including: memory, LCD, Camera, serial port, IIC, IIS and USB interface control circuits.

3.2 Software design

We choose the embedded linux operating system, the version number is: 2.6.12.

It is the running platform for local image acquisition program, compression program, USB2.0 controller CY7C68013A driver and its applications.

Figure 3 Main program flow chart

3.2.1 System initialization

System initialization includes the initialization of chips OV511, OV7260, USB2.0 controller CY7C68013A, wireless transceiver chip nRF2401 and the initialization of the Linux system. The initialization of the Linux system mainly completes the initialization of CPU, SDRAM and other chips, loads the drivers of the camera and USB2.0 controller [5], and prepares for the execution of the application program. The initialization of other chips mainly performs corresponding operations on some data registers, address registers, and interrupt service registers.

3.2.2 Real-time image transmission process

After the system initialization is completed, the application program we wrote controls the camera driver to capture an image signal and save it in the flash disk. The program flow is shown in Figure 4. The image file at this time is in uncompressed PPM format, and then JPEG compression The program compresses pictures in PPM format into pictures, as shown in Figure 5. The average file size of a picture with a resolution of 320*240 is only 8KB, which can fully meet the needs of wireless transmission. After the compression is completed, the picture in JPG format is read. file, and sends the image data to the driver of the USB2.0 controller CY7C68013A, and then the driver writes the data to the endpoint buffer of the USB2.0 controller. Finally, the USB2.0 controller CY7C68013A controls the nRF2401 to write the endpoint buffer The image data in the system is sent out wirelessly, and the program flow is shown in Figure 6.

Figure 4 Image acquisition program flow chart.

Figure 5 JPEG compression encoding program flow chart

Figure 6 nRF2401 wireless transmitter program flow chart

In the entire system, the Linux operating system completes the initialization of each chip, coordinates the work between the CPU and other chips, and completes the reading, compression and sending of image data (Figure 3).

4 Design of picture receiver

The picture receiver we designed is a PC-based wireless receiving device similar to a wireless network card. It completes the reception and display of picture information. The hardware structure is the same as the nRF2401 wireless transmitter module, and the USB2.0 controller CY7C68013A is used to control the nRF2401. Wireless transmission, as shown in Figure 7.

Figure 7 Picture receiver structure

USB2.0 controller CY7C68013A controls nRF2401 to receive image data wirelessly. The program flow is shown in Figure 8. Then the application on the PC calls the read function in the USB2.0 controller driver to receive the image data and save it, and finally displays the image. . As shown in Figures 9 and 10.

Figure 8 nRF2401 wireless receiving program flow chart.

Figure 9 Pixel: 320×240.

Figure 10 Pixel: 640×480 wireless camera.

5 Conclusion

The wireless camera of this system uses a 32-bit high-performance ARM processor S3C2440A equipped with a 2.6 kernel Linux embedded operating system for core control, and excellently completes picture shooting, compression and wireless transmission. The receiving end receives and saves the picture information in the PC hard disk. If necessary, it can also be transmitted to the server for remote monitoring. It can be used in car anti-theft monitoring, cordless video phones, and mine operation monitoring. Therefore, the successfully developed wireless real-time image transmission system has broad application prospects and markets.