Automobile engine ignition coil test system based on single chip microcomputer and digital signal processor

1. Introduction
With the widespread application of automotive electronic ignition technology, the requirements for various components of the electronic ignition system have also increased. As an important component of the automotive electronic ignition system, the performance of the ignition coil is directly related to the working condition of the vehicle. Therefore, it is necessary to accurately test the various parameters of the ignition coil and establish strict product factory inspection standards. According to surveys, most of the domestic online test equipment for automotive ignition coil systems in China is old-fashioned equipment, and there are few intelligent detection equipment. Imported equipment is expensive and its intelligence level is not high. [1] Therefore, developing an automated and intelligent automotive engine ignition coil test system is the direction of scientific research. This paper focuses on the design method of this automotive engine ignition coil test bench that meets the requirements of modern production.
2. System composition
The principle block diagram of the automotive engine ignition coil test bench is shown in Figure 1. The hardware of the automotive ignition coil test bench system mainly consists of the test piece (coil, load), programmable signal source, programmable voltage source, I/O control board, data acquisition and processing system, industrial computer, etc. Among them, the load, programmable signal source, and programmable voltage source are used to simulate the working condition of the ignition coil; other components are used for measurement and control. According to relevant national standards, the various parameters of the ignition coil must be measured under corresponding conditions (different test items may have different conditions), and the test conditions of coils with different signals are also different. Therefore, the voltage source and signal source that provide working conditions for the ignition coil can be set by the system software in the host computer through the serial communication interface. In order to be able to test different secondary coils of multi-head coils (four-head, six-head, etc.), the signal source is sent to the device under test through the measurement control circuit. The measurement control circuit consists of various relays and input and output lines. The relay performs corresponding actions according to the control commands issued by the IO control board to determine which signal source to send out and which signal to be tested is connected to the data acquisition system. The IO control board and the data acquisition card are directly connected to the industrial computer through the ISA and PCI buses respectively. The host computer software directly operates the IO port to operate the IO control board. The data acquisition and processing system communicates with the system test software through the driver. The tester only needs to operate the system test software of the host computer to measure the various parameters of the ignition coil. [2][3]

Figure 1 Schematic diagram of the automotive ignition coil test bench
From the above, it can be seen that the ignition coil test system is essentially a data acquisition and processing problem. Therefore, the design of the data acquisition card naturally becomes the most important problem in this system. The implementation of each part is introduced below.
3. Hardware implementation
3.1 Data acquisition card
Analyzing the secondary voltage signal of the ignition coil, it can be seen that the highest effective bandwidth of the signal is 5MHz. According to the sampling theorem, the highest sampling rate of the system is at least 10MHz. For such a high sampling rate, a high-speed data acquisition system must be used to test in order to meet the test requirements. [1] Figure 2 is a structural block diagram of the data acquisition part of this system.

Figure 2 Structural block diagram of the data acquisition system.
The acquisition part processor uses TI's DSP chip TMS320VC5402 . Its processing speed can reach 100Mbps, with an improved 8-bit HPI interface, 16Kxl6Bit DARAM, and 4Kx16Bit ROM storage space, with a high cost performance. Since the internal ROM of TMS320C5402 is not writable, an external 27040EPROM is used as an external program area to store programs. Because the ignition coil data acquisition requires high speed and high precision to meet the requirements of high-end and mass production. At the same time, in order to expand the application field of this acquisition system, the A/D converter uses the AD9432 chip of the American AD company. This chip is a 12-bit single-channel analog-to-digital converter with a maximum conversion rate of 100MHz. The input signal analog bandwidth can reach 500MHz, the sampling clock is a PECL differential level input, and the conversion data is a 1TTL level output. The chip has an input cache and a sample and hold, and a 12-bit parallel data output. Since AD9432 requires a differential input form, the input signal must be converted into a differential form through a signal conditioning circuit. [4]
Since the system requires high-speed data acquisition, the high-speed cache is a key link in the system. The high-speed cache is a key link in the system. According to the requirements of the system, CY7C4255 can be selected. CY7C4255 is a high-speed, low-power 8k*18 low-voltage synchronous first-in-first-out (FIFO) memory with a read-write cycle of 10ns. It has independent 18-bit input and output interfaces and read and write clock signals, which can realize synchronous read and write operations. The data after A/D conversion is continuously written into FIFO, and DSP decides how to read the data according to the status of FIFO. The speed at which DSP reads and processes this number is much higher than the speed of A/D conversion. Every time DSP actively reads FIFO data, it executes a conditional read instruction, that is, it reads only when FIFO is not empty (EF=BIO is high), and DSP waits when FIFO is empty. When DSP has a heavy processing task, FIFO data has not been read for a long time. When FIFO is half full or full, an interrupt signal will be sent to DSP, DSP will suspend the current work, enter the interrupt service program, and process the data in FIFO. By transferring the sampled data to the memory through FIFO, not only a high-speed sampling rate of about 100MHz is obtained, but also the writing of sampling program is greatly simplified. [page]

The PCI interface chip uses PLX's PCI9052, which is a high-performance PCI interface chip for low-end applications. The connection between the interface chip and TMS320VC5402 is relatively simple and will not be discussed here.
The software design of the sampling system mainly includes two parts: reading and processing data in the DSP and developing the device driver for the acquisition card. This article mainly uses assembly language to implement DSP programming on the CCS platform. The PCI device driver development uses a framework designed by Microsoft for the driver of the Windows9x operating system - VxD.
3.2 Programmable voltage source and programmable signal source
According to the test conditions of various types of coils, the programmable voltage source must be able to generate a continuously adjustable DC voltage of 3-25V. The programmable signal source can generate a continuously adjustable Hall wave signal with a frequency of 0.5-250Hz (minimum step 1HZ), an amplitude of 0-10V, and a duty cycle of 1%-99% (minimum step 1%).
The design of the programmable voltage source is realized by adding a control board to an industrial finished product. Specifically, it is to buy a voltage source that meets the requirements and can be easily developed (controlled), and then make a control board according to the instructions of the voltage source. There are many such voltage sources on the market, and the production of the control board is relatively simple, so I will not go into details here.

Figure 3 System block diagram of programmable signal source
From the above indicators, it can be seen that the frequency variation range of the programmable signal generator is wide, and the requirements for stability and accuracy are very high, and there are certain automation requirements. These are difficult to achieve with analog circuits, so we use a fully digital circuit controlled by a single-chip microcomputer. The system block diagram is shown in Figure 3.
There are many ways to generate pulse waveforms, but the key is how to make the duty cycle variable. Here, the software is used to control the output port of the single-chip microcomputer, and the method of setting and clearing it regularly is implemented, so that the duty cycle can be easily adjusted, and the frequency is also variable. After calculation, it can be found that when the frequency is 250Hz and the duty cycle is 1%, the signal remains at a high level for 40µS, so the speed of the MCS-51 single-chip microcomputer can meet the requirements. 【5】
3.3 IO control board and measurement control circuit
When introducing the system composition, the function and composition of the measurement control circuit were also explained. The following is a brief introduction to the design and implementation of the IO board. The IO board here is only composed of a simple parallel interface chip 8255A, and this board is directly plugged into the ISA expansion slot of the industrial computer (if there is no ISA slot on the industrial computer, it can also be directly connected to the PCI slot). The upper computer software only needs to write some control words to operate the IO board, which can make the output of the IO board change accordingly, thereby driving the corresponding relay in the measurement control circuit to perform corresponding actions. We know that in the Windows 9x operating system, the application software can directly access the registers in the interface circuit without the need for a driver. Therefore, if the upper computer in this system uses Windows 98 as the operating system, there is no need to write a driver for the IO board. This is one of the main reasons why the author uses Windows 98 SE as the operating system in the industrial computer of this test system.
4. System software design
The system software includes the upper computer software and the lower computer software. The design of the lower computer software has been mentioned when introducing the hardware implementation of each part, so it will not be repeated here.
The host computer program design can be divided into four parts: the design of the test interface, the design of the database for storing measurement results and test parameter settings, the design of the serial communication program between the host computer and the slave computer, and the design of the measurement algorithm.
The host computer software is implemented using Visual Basic 6.0. Visual Basic 6.0 is a simple, easy-to-learn, and efficient visual programming language development system under the Windows environment. VB6.0 can use DLL to implement the input and output functions of the IO port, and can also implement serial communication through Mscomm controls or API functions. It can easily realize image display and data storage, and can also give full play to the VB database function and generate user interfaces quickly. Therefore, it is just right to use VB6.0 to implement this system. Here we introduce how to access the port of the IO board inserted in the I/O slot of the industrial computer under VB6.0.
Since VB cannot directly operate registers and has no direct input and output port operation statements, and VC++ has the functions and characteristics of both assembly language and high-level language, if VC++ is used to compile a dynamic link library, the library contains read/write functions for input and output ports, and then in the VB program, by declaring the functions in the DLL and providing the DLL path to call these functions to complete the control behavior, then the operation of the IO port can be easily realized in VB.
5. Conclusion
The implementation method of the automobile engine ignition coil test system introduced in this article is actually applied to the ignition coil test bench developed by the Automotive Electronics and Electrical Research Institute of Wuhan University of Technology for Guangzhou Feida Electric Co., Ltd. and Beijing Tongxiang Tongyue Automotive Electronics Co., Ltd., and achieved good results.
The author's innovation: The ignition coil test system discussed in this article can measure all the parameters of the ignition coil specified in the national standard, so as to replace imported equipment and fill the domestic gap. In addition, the accuracy and precision of the automobile engine ignition coil test have reached high requirements, and the performance of existing domestic equipment has been improved.