Abstract: This paper introduces an instrument with a single-chip microcomputer as the core, which can test the relevant parameters of the rack performance of 3-disc DVD and CD players. It also introduces in detail the development ideas, measurement principles and system hardware and software structure of the instrument.
Keywords: C52; DVD; CD; test
IntroductionIn
the past two years, single-disc DVDs have gradually developed into 3-disc or even 5-disc DVDs. The disc selection mechanism of the movement has also become increasingly complex. For this reason, movement manufacturers tend to provide customers with complete rack components, including the movement and a full set of tray transmission and control mechanisms. However, since the main transmission components of the rack component are plastic parts, they are prone to deformation. The transmission performance is not easy to control during mass production, making it difficult to determine the appropriate parameters when writing system software, resulting in the finished product The whole machine often has faults such as the disc not turning in place. In order to control the quality of the transmission mechanism of the 3-disc DVD/CD rack assembly, it is necessary to test the relevant parameters to control the quality of components and assembly. To this end, we developed a performance tester for the 3-disc turntable mechanism based on the characteristics of the 3-disc DVD/CD movement produced by Thomson to solve the quality control problem in the production of 3-disc DVD/CD players.
Application Overview
The tester uses the AT89C52 microcontroller as the core, equipped with function control buttons and two-line LCD character display. The interface signals provided on the rack are used to measure the various time parameters, film selection function, brake performance and other parameters of the turntable during operation, so as to monitor the production quality and track and improve the quality at any time. The circuit
connection relationship of the product when used for testing is shown in Figure 1, where the position sensor signal comes from the three optical choppers on the rack motor board, which monitor the turntable position, door entry status and door closing status respectively. The motor control signal can control the entry and exit (open and close the door) of the optical disc tray, film selection and other actions.
System structure and principle
The system structure of the tester is shown in Figure 2. The main control chip is the single-chip microcomputer AT89C52, with built-in 8K program space and 256Byte RAM space, which mainly completes the functions of measurement, display, motor control, keyboard scanning, etc.
The function keys include single-step/continuous rotation selection key (selecting whether the turntable rotates continuously or rotates one disk at a time), door opening and closing control key, and movement up and down control key (controlling the movement up and down). The movement selection jumper is used to select whether the rack being tested is CD or DVD. Due to the different structures of these two different racks, the software algorithms are different during the test. The LCD display uses a 2x16 character LCD module, which can display the measurement result data in two lines of Chinese, and is divided into two screens. The control of the motor is divided into two channels. One channel controls the door opening and closing motor, and then controls the opening and closing of the tray box, which is driven by the motor driver IC LB1641. The other channel controls the motor of the film selection turntable, and then controls each time the disc is rotated into place, which is driven by a discrete component transistor. Position detection is performed using the optical chopper RPI-574 on the motor board. Three choppers are placed in different positions to detect door opening, door closing, turntable rotation speed, etc.
The serial port drive circuit leads to a standard RS-232 port, which can be connected to a PC, so that the tester can be controlled by the PC host software.
Figure 1 Tester application connection circuit
Figure 2 Block diagram of 3-disc DVD rack performance tester
Figure 3 Turntable rotation parameters
Figure 4 Tester software flow chart
Measurement and control principle
In the Thomson TC3C/TC3D product specification, the parameters of the turntable when rotating are specified as shown in Figure 3 (taking TC3C as an example): Among them, the waveform shape of the DISCPOS signal is determined by the disc position marking groove under the disc selection tray, and the shape of the waveform is also the shape of the groove. When the turntable rotates, different positions of the groove will pass through the optical chopper, and the detector will output the corresponding continuous waveform. When the damping condition of the transmission mechanism changes, the length of different time periods on the waveform will also be different. If the values of these variables exceed the range specified in the Spec, it will cause difficulties in software identification of the disc position and control, which will cause logical confusion and cause product quality problems. This tester measures these variable values through the internal timer of the microcontroller, and compares them with the values in the Spec to judge the quality of the product.
The DISCPOS signal is input into the AT89C52 from the I/O port, and the length of different position segments is calculated by the level judgment method to measure the parameters in the Spec. We choose T2, T2a, T7, and Tskip as measurement parameters to reflect the operation and damping state of the transmission mechanism at different gear positions. T7 is tested in two states: without brake pulse and with brake pulse, respectively, to simulate the transmission damping conditions of free rotation and film selection, so as to correspond to the actual use state.
The control of the turntable motor is completed by the Discskip signal. When Discskip=1, the DC motor is driven to rotate. If a PWM wave is generated on the Discskip signal, the motor speed can be controlled and the braking action can be implemented. The brake starts from point D. According to the product specification, the brake strength varies with the rotation speed. The rotation speed is based on the pre-measured length of T2. In this way, according to different damping conditions, the brake strength can be automatically and instantly adjusted so that the turntable can stop completely at point E, thereby improving the compatibility of the product. The
door opening and closing motor is controlled by the Drawer_in/Drawer_out signal. Discpos1 and Discpos2 signals are used to monitor the door opening and closing conditions respectively. When Drawer_in is valid, the motor drives in the direction of door closing. Once the door is detected to be closed, the drive stops. Vice versa.
Software flow
The software is the core of the system, which is compiled in C51 and compiled under Keil C system. It is debugged by Manley's simulator SE-52. It is mainly composed of initialization, measurement and calculation, turntable motor drive and PWM wave generation, door opening and closing control and movement up and down control, LCD display module, etc. The corresponding functions are different for CD rack (TC3C) and DVD rack (TC3D). When measuring, it will be automatically selected according to the jumper setting. Its program flow is shown in Figure 4.
Conclusion
This tester has a compact structure, simple operation, clear display, low cost, and has been successfully used in production. Although the development of this tester uses Thomson's TC3C/TC3D module as the test object, its test principles and methods are also applicable to similar products of other companies (multi-disc DVD/CD rack modules). At that time, you only need to make a small change to the parameters in the software according to the Spec of the specific product to complete the same function. ■
References:
1 Product Specification: TC3C 3disc carrousel-Thomson Multimedia. 2002.4
2 Lai Qiwen. "8051 Microcontroller C Language Development Environment Practice and Design". Science Press. 2002.1
About the author: Li Lidong, male, graduated with a master's degree from the Optoelectronics Department of Zhejiang University, and is currently a senior electronic engineer at Tom Sheng Optical Components (Shenzhen) Co., Ltd.
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