Design of intelligent data collection system for pointer instruments

Pointer instruments are widely used in scientific experiments and production because of their simple structure, easy maintenance, no electromagnetic interference, high reliability, and low price. When instrument inspection departments and instrument observation units observe instruments, their readings are usually completed manually. The reading errors are caused by visual errors of personnel, and the reading speed is slow, the labor intensity is high, the observation cycle is long, the work efficiency is low, and it is easy to cause problems such as low reading accuracy, poor reliability, and high repetition rate. At the same time, after long-term use of pointer instruments, surface contamination also brings difficulties to manual reading. Therefore, how to realize the automatic interpretation of pointer instruments and improve observation efficiency and observation accuracy has become a problem that needs to be solved.
With the continuous development of digital signal processing and digital image processing technology, the method of designing intelligent recognition of pointer instruments using these two technologies has attracted people's attention. This paper adopts DSP technology and develops a set of pointer instrument data intelligent acquisition system based on the idea of ​​Hough transform. Practice has proved that the system has the advantages of high reading efficiency, accurate reading, and high reliability.

1 Research status
After the 1960s, with the continuous development of digital image processing, pattern recognition, computer technology and artificial intelligence theory, machine vision technology has made great progress and has been widely used in many fields. The so-called machine vision technology mainly uses computers to simulate human visual functions, extract information from the images of objective things, process and understand them, and finally use them for actual detection, measurement and control.
In the process of automated production, machine vision systems have been widely used in fields such as working condition monitoring, finished product inspection and quality control. The characteristics of machine vision systems are that they can improve the flexibility and automation of production. In some dangerous working environments that are not suitable for manual operations or where artificial vision is difficult to meet the requirements, machine vision is often used to replace artificial vision. At the same time, in large-scale industrial production processes, machine vision detection methods can improve production efficiency and the degree of automation of production. It is the basic technology for realizing computer integrated manufacturing.
In the measurement of pointer instruments, there are frequent and large-scale visual comparisons of the positions of pointers and scales, which is exactly the field where machine vision technology can play an advantage. At present, there are few products that use automated calibration devices in the calibration of pointer instruments, and conventional detection methods are basically used. Automated calibration devices have been in progress as a research direction. If the automatic calibration system is successfully developed and put into use, it will reduce the labor intensity of testers and the measurement uncertainty caused by human factors, which is of great significance to ensure the accuracy and reliability of calibration.
Li Tieqiao and others from Harbin Institute of Technology were the first to conduct image recognition of pointer instruments in China, mainly studying pressure gauges. Wang Sanwu and others studied the image recognition and verification system of water meter multi-dial. Li Baoshu and others mentioned the identification of pointer scale lines, but these studies did not deviate from the identification method of pointer deflection. Then there are some recognition schemes and designs for compasses, some instruments of cars, and zero-position instruments in aircraft cockpits. The above studies show that the research method of automatic reading recognition of pointer instruments mainly obtains the angle of the pointer and calculates the reading of the instrument based on the angle relationship. Unlike the manual reading method, the reading is not calculated based on the positional relationship between the pointer and its two closest scales, avoiding the lack of reading accuracy.
In this paper, an intelligent acquisition system for pointer instruments based on Hough transform is designed, which realizes the functions of image acquisition, processing, storage, display reading, communication, etc., and submits the final data to the host computer database for storage, as shown in Figure 1.

2 System Hardware Design
According to actual needs, the pointer instrument data intelligent acquisition system needs to complete image acquisition, processing, storage, output, reading, communication and other functions, and has high requirements for data processing capabilities. The Blackfin series processors are high-performance embedded DSPs jointly developed by AD and Intel for high-speed embedded digital processing. Among them, the performance of ADSP-BF533 reaches 1 200 MMACs when the clock frequency is 600 MHz, which can well meet the requirements of digital controller processing capabilities. Therefore, BF533 is used as the core processor, and SDRAM, Flash, CMOS image sensor, RS485 serial bus splitter, etc. are used as peripheral circuits to build a pointer instrument identifier platform. [page]

2.1 DSP core power circuit module
DSP-BF533 uses dynamic power management technology to reduce chip power consumption. The chip's VRout pin provides on-chip PWM switch control. Therefore, only a basic switching power supply circuit needs to be connected externally to achieve dynamic adjustment of the power supply voltage. AMS117-3.3 is used to convert the 5 V voltage to 3.3 V. According to the principle of switching power supply, the VRout pin is used to control the on-off of the field effect tube FDS9431 to adjust the output voltage DSP_VDD_INT. The circuit connection is shown in Figure 2.

2.2 Flash storage circuit module
Since DSP-BF533 does not have internal program memory, an external Flash is required to store the program. In addition, the calculation results and working status during program operation also need to be saved when the power is off. The EBIU unit of DSP-BF533 provides an asynchronous memory interface (Asynchronous Memory Interface), which can realize the reading and writing of CFI standard Flash. The circuit uses Flash AM29LV800 as the programmer and working data memory. The AMS0 of the EBIU interface is used as the chip select signal, the AWE and AOE signals are used as read and write control signals, the address bus and data bus are connected to the address bus and data bus of the EBIU, and the Reset pin is connected to the system reset signal. The circuit connection is shown in Figure 3.

2.3 TFT LCD display circuit module
TFT LCD uses PT035TN01 24-bit true color LCD with a resolution of 320×240. After power-on, DSP initializes the LCD through the SPI port, sets the data format to 8-bit data bus mode, and provides R, G, and B three-color signals in 3 clock cycles. DSP sends R, G, and B data to LCD through the PPI port in DMA mode, and uses timers Timerl and Timer2 to generate VS and HS synchronization signals to scan the LCD. The circuit connection between DSP and LCD is shown in Figure 4.

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2.4 COMS camera circuit module
Image acquisition is the premise of pointer recognition. In order to make the pointer angle recognition have a higher accuracy, the image needs to have a higher resolution. After Maflab simulation, the image resolution is 0.5° when it is 800×600. The TGA130V10 module is selected in the circuit. This module uses the OV9653 COMS sensor and supports a maximum resolution of 1 280×1 024. The module configures OV9653 through the SCCB bus. After the configuration is completed, OV9653 can output YUV signals in VGA or SVGA mode. The COMS camera is connected to the FPGA, and the OV9653 is configured through the FPGA simulating the SCCB bus, and the image data is transmitted. The reset and PWDN signals are provided by the FPGA. The COMS port connection is shown in Figure 5.

2.5 Flash connection circuit
In order to enable the instrument to work in a darker environment, a flash circuit is designed in the circuit. The flash light source uses a white LED, and the MAX1583 of Maxim Company provides the LED with the instantaneous large current required for flashing. The DSP sends the flash operation instruction to the FPGA through the SPI port. After decoding, the FPGA controls the MAX1583 to perform the corresponding operation by setting Mode1 and Mode2. The circuit connection is shown in Figure 6.
2.6 RS485 connection module
RS485 is used as the communication interface between the system and the host computer in the design. In industrial automation control, the data of some dials need to be monitored in real time. The RS485 interface can quickly form a monitoring network. Each identifier in the network has its own specific ID. The host computer can obtain the real-time data of each dial by cyclically sending the ID of each identifier. The MAX13433 of Maxim Company is used as the RS485 transceiver converter in the circuit. MAX13433 is a full-duplex RS485 transceiver that allows direct low-voltage ASIC and FPGA connection without additional devices. The transceiver operating voltage is 3~5V, and the logic interface operating voltage is 1.62~5V. 3.3 V voltage is used in the design. The UART_RX and UART_TX pins of DSP are connected to RO and DI of MAX13433 respectively, and the RS485_DE and RS485_RE signals provided by FPGA are connected to DE and RE of MAX13433 respectively. DSP sends instructions to FPGA through SPI port, and FPGA decodes and outputs the corresponding RS485_DE and RS485_RE to control the transmission and reception of the device, realizing RS485 bus transmission. The circuit connection is shown in Figure 7.

3 System software design
The software design of the pointer instrument data intelligent acquisition system includes two parts: DSP software design and host computer software design. AD's DSP development environment VisualDSP++Developm-ent has a good interface, powerful functions, and supports C language development, so the DSP software uses the VisualDSP++5.0 software design platform.
The host computer program uses database technology and the Delphi7.0 software design platform. The pointer instrument intelligent acquisition system is programmed in C language, mainly including the main program, keyboard processing subroutine, pointer recognition and reading calculation subroutine, and serial communication subroutine. The implementation of each program module ensures the feasibility and reliability of the system. [page]

3.1 Main program flow chart
The main program flow is shown in Figure 8. After the system is powered on, it is initialized and configured for each peripheral. Press any key to enter the measurement state. There are two measurement modes, automatic timing measurement mode and manual measurement mode. In each mode, the user measures data according to actual needs.

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3.2 Keyboard processing subroutine flow chart
The keyboard processing subroutine flow chart is shown in Figure 9. When designing the system, the keys are minimized for ease of use. The measurement mode selection and flash mode selection each contain two modes. The default is manual measurement mode and no flash measurement mode. The time interval setting adopts three-choice mode, and the user does not need to enter it by himself. The data transmission adopts the one-key transmission mode, which is used in conjunction with the confirmation key.

3.3 Pointer recognition and reading calculation flow chart
The pointer recognition and reading calculation subroutine mainly completes the reading and calculation functions of the instrument. The accuracy and error of the final reading are determined by this process. The program first converts the color image into a grayscale image, and then detects the edge of the image by using the Sobel operator to segment the grayscale image edge. The basic idea of ​​Hough transform is used to determine the pointer position, and the actual reading of the instrument is calculated according to the instrument range. The process is shown in Figure 10.

3.4 Serial communication subroutine
The serial communication subroutine flow is shown in Figure 11. When the user presses the data transmission key and confirms, the system reads the data stored in the Flash according to certain storage rules, and sends the hexadecimal data through the serial port according to the corresponding combination algorithm until all the data is sent and a sending end flag is sent. After the host computer receives the data, it will send back a successful data reception flag to the system, and the system will automatically clear the data in the Flash.

4 Conclusion
Combining VisualDSP integrated development environment and serial port data receiving software, the pointer instrument data intelligent acquisition system was programmed, software debugged and hardware simulated. The results show that the system has a compact structure, good stability, accurate and reliable data acquisition and low price.