Industry: Consumer Goods Products: CompactDAQ, Portable DAQ, Multifunction DAQ, LabVIEW, PXI/CompactPCI The Challenge: This project highly integrates various types and formats of video signal sources, data acquisition, instrument control, and signal switching functions. Software analysis and judgment of video and other signals significantly improves testing efficiency, achieving automation, parallelization, and generalization of complex testing processes. The Solution: Using NI's PXI platform and hardware modules, signal generation, acquisition, switching, and control are performed. NI's graphical programming software LabVIEW is used for test process control, data analysis and judgment, and user interface development. Combined with programmable power supplies and parallel testing methods, a flexible and automated testing system is achieved. I. Working Principle and Test System Requirements of the Audio/Video Signal Processing Board The audio/video signal processing board is the small signal processing module of a CRT television (hereinafter referred to as the small signal board). The principle of a certain model of small signal board is shown in Figure 1. It decodes and processes TV RF signals and various types of video signals, converting them into images and synchronization signals suitable for CRT scanning; it provides one Video Out video output signal for use by external video devices; it switches and processes audio input signals, sending them to speakers and Audio Out audio output interfaces. The MCU controls each module via the I2C bus and receives user operation commands via remote control (IR) and key (KEY) interfaces. [align=center]Figure 1 Working principle of the small signal board[/align] Based on the working principle of the small signal board, the basic requirements for the test system are as follows: 1) Provide multiple DC regulated power supplies to provide operating power for the small signal board. 2) Provide TV RF signals; provide analog video signals such as Video, S-Video, YUV, and VGA; provide HDMI digital audio and video signals; provide analog stereo audio signals. 3) Can simulate remote control and key signals to control the small signal board. 4) Provide horizontal and vertical feedback signals to ensure the small signal board operates normally. 5) Can acquire multiple DC signals and low-frequency AC signals; can acquire and output switch signals. 6) It can simultaneously acquire 3 video signals. II. Solution Design 1. Based on the existing test system, we hope the new test solution can achieve the following: 2. High integration, minimizing space occupation. 3. Automation, minimizing the impact of human factors. 4. Versatility, adaptable to different models of small signal boards, reducing redundant development work. 5. High efficiency, with the shortest possible single-board testing time to meet production cycle requirements. 6. High detection rate, allowing testing of intermediate parameters of interest, improving coverage. Through test requirement analysis, virtual instrument technology perfectly meets the solution requirements and can achieve the expected results. NI has a rich product line of virtual instrument test and measurement systems, providing us with a wide range of choices. LabVIEW is an easy-to-learn and easy-to-use software that can be used to quickly develop complex, parallel, efficient, and easy-to-operate test systems. Therefore, we decided to choose NI's hardware and software platform to develop the new test system. The overall design scheme is shown in Figure 2. The programmable multi-channel power supply is a redesigned version of our company's previously developed CNC power supply, featuring 3 programmable and 3 fixed voltage outputs. These 6 voltage outputs are distributed into two independent channels, capable of simultaneously powering two small signal boards. The power supply capacity reaches 2 x 6 x 25W. The output voltage range is 1.5-50V. A serial port has also been added, allowing for computer programming to power different models of small signal boards. The TV RF signal is provided by the central signal system, while the analog video signal is generated by the PXI-6541 high-speed digital I/O and simple peripheral encoding circuitry. The HDMI signal utilizes our existing USB-HDMI module, redesigned into a 4-channel HDMI signal generator, capable of simultaneously powering two small signal boards. The remote control signal is generated by the digital output DO of the M-series DAQ card PXI-6259, and the button signal is generated by the analog output AO of the 6259. The horizontal feedback signal is generated by the 6259's counter; the vertical feedback signal is directly fed back after being shaped from the vertical output sawtooth wave. For DC, low-frequency, and switching signals, the 6259 is used for acquisition or processing. Three-channel video acquisition is accomplished by two PXI-5112 digitizers. The industrial digital I/O module PXI-6515 controls power on/off and the operation of protective relays; the relay module PXI-2530 handles the switching of video synchronization signals and other signals. The signal conditioning circuit performs signal range transformation, signal protection, buffering, and interface conversion. The scanner is connected via the USB port provided by the PXI-8196 controller. The voltage of the programmable power supply is set via the serial port, and a network interface is used to connect to the local area network. To ensure compatibility with various small signal boards, a universal test bed base was designed. The base and bed of needles are connected via a socket; when testing other small signal boards, only the bed of needles needs to be replaced and the corresponding software configuration called. To significantly improve testing efficiency, a parallel working approach is adopted, with two small signal boards tested simultaneously. Only when testing RGB and Video signals is a step-by-step test employed due to the limited number of digitizers. [align=center]Figure 2 Overall Scheme Block Diagram[/align] III. Implementation of Key Module Hardware and Software 1) Driving the Small Signal Board: To enable the small signal board to enter normal working state, it needs to be provided with horizontal and vertical feedback signals. The horizontal output is a 33K-34K square wave, and the horizontal feedback signal is a square wave that follows its frequency and has adjustable phase and duty cycle. Utilizing the retriggerable feature of the counter in NI's M-series data acquisition card PXI-6259, the horizontal feedback signal can be easily generated. The horizontal output signal is used as a trigger signal to trigger the Counter, causing it to continuously generate pulse signals with the same frequency as the trigger signal. Its front panel and program are shown in Figures 3 and 4. By adjusting High ticks, low ticks, and Idle Status, the duty cycle and phase of the pulse waveform can be adjusted, thereby realizing the required horizontal feedback signal. Because the small signal board does not have strict phase and duty cycle requirements for vertical feedback, the vertical output sawtooth wave can be used as the vertical feedback signal after simple shaping. [align=center] Figure 3 Front panel for line feedback generation Figure 4 Line feedback generation program diagram[/align] 2) Generation of various types and formats of video signals For PCB module-level production testing, there is no need to debug image parameters. Only simple images are needed as test signals, such as color bars, squares, and grayscale. Here, we use color bars as test signals. Using NI's 50M 32-channel high-speed digital I/O (PXI-6541) in conjunction with a simple peripheral video encoding circuit, various types and formats of color bar signals can be realized. VGA signal generation: RGB and horizontal and vertical signals are directly obtained by buffering from digital I/O, which can realize VGA, SVGA, XGA, and SXGA format color bar signals. YUV signal generation: 6541 generates RGB signals and synchronization signals. RGB and synchronization signals are converted into YUV signals through a processing network, realizing YUV color bar signals that support all formats from 480i to 1080p. Video (CVBS) signal generation: The 6541 generates RGB and composite sync signals, which are then used by a video encoding chip to generate standard Video and S-Video signals. A BMP color bar image corresponding to the signal type and resolution is drawn using drawing software, and then converted into a digital waveform suitable for transmission by the PXI-6541 by the subroutine shown in Figure 5. The HDMI signal is derived from a modified USB-HDMI module, integrating and centrally controlling four modules to achieve a low-cost, highly integrated HDMI signal source that supports 480i-1080P formats and digital audio. Practical application shows that the generated signal quality fully meets the test requirements. [align=center] Figure 5 Subroutine for generating color bar signal digital waveform[/align] 3) Video signal acquisition and analysis: The small signal board decodes and frequency-converts various input video signals to generate RGB signals to drive the picture tube, as well as standard Video signals for external devices. Therefore, we use two NI PXI-5112 chips to acquire the RGB and Video signals. The PXI-5112 is a digitizer with 2-channel synchronous sampling and a real-time sampling rate of 100 MS/s. Because color bars are used as the test signal, the bandwidth of the RGB signal is <1MHz, and the bandwidth of the Video signal is <4.5MHz. To reduce data processing load, the sampling rate of the 5112 is set to 10MHz for RGB acquisition, while a 50MHz sampling rate is used for video output. The 5112 lacks a video trigger function; to reduce computation, an external synchronization separation circuit is used. The RGB and video signals are triggered by field synchronization, and one field of signal is acquired for analysis and processing each time. LabVIEW's rich signal processing, measurement, and analysis functions are used to process the signal, measuring parameters such as signal amplitude, synchronization amplitude, pulse width, frequency, waveform overshoot, preshoot, and subcarrier amplitude and frequency. Furthermore, the difference rate between the signal and the standard waveform is calculated through alignment comparison to determine signal quality. The video analysis subroutine is shown in Figure 6. [align=center]Figure 6 Video Analysis Subroutine[/align] 4) The analog signal board for remote control codes and buttons directly receives the demodulated remote control commands. We only need to simulate the unmodulated remote control codes. It is a TTL level pulse train, which can be simulated by the digital output DO of the 6259. The clock of the DO needs to borrow the internal clock such as AI/O or other external clocks, but AI/O and remote control codes cannot work synchronously, and the two Counters are already occupied, so other external clocks can only be used. The transmission of remote control codes is only enabled when the small signal board is working normally. We can use the 34K square wave of the line feedback signal output by the Counter as the clock for the remote control codes. Once the small signal board is working normally, the line feedback signal is very stable, and using it as a clock can meet the accuracy requirements. In addition, the DO of the 6259 can continuously output 2047 pulses, which can continuously send about 10 sets of remote control commands, meeting the test requirements. After verification, the simulated remote control commands work stably and reliably. The remote control code simulation subroutine is shown in Figure 7. First, the remote control encoding subroutine obtains the remote control code waveforms for all buttons on various remote controls. Then, this subroutine sends the remote control codes out through the DO of the PXI-6259. Television buttons are usually AD type; here, the analog output AO of the 6259 is used. After measuring the standard voltage corresponding to each button, the button function can be realized using the AO of the 6259. The duration and interval of the simulated button press are 20ms, which is faster than manual button operation. [align=center] Figure 7 Remote Control Code Simulation Subroutine[/align] 5) Processing of DC, Low-Frequency Signals, and Digital Switch Signals The PXI-6259 has a multi-channel acquisition rate of up to 1 MS/s, 16-bit accuracy, 32 analog inputs, 4 analog outputs, and 48 digital I/Os. Utilizing the rich and comprehensive functions and high performance of the 6259, it can meet the requirements for the acquisition or generation of DC, low-frequency AC signals, switch signals, etc. The final actual test system hardware is shown in Figure 8. The hardware system highly integrates the functions of many traditional instruments while significantly reducing the space occupied. [align=center] Figure 8: Photo of the test system[/align] IV. User Interface and Auxiliary Functions The test software is developed using the LabVIEW platform. It effectively connects various test modules, controls the test process, and displays the test results on the screen. Upon completion of the test, it stores all test parameters and results on the hard drive for later traceability and querying. The software fully utilizes the parallel execution capability of LabVIEW programs, allowing subroutines such as line feedback generation and small signal board status monitoring to run simultaneously with the test program, solving the problems of small signal board driving and monitoring. The test software provides a user-friendly interface, as shown in Figure 9. It allows users to load configuration files, customize test items, and modify the upper and lower limits of test parameters, and can query, statistically analyze, and perform analysis on test reports as required. [align=center] Figure 9: Software User Interface[/align] V. Testing After the system was completed, we set some conditions to test the actual performance of the system. The average single-board testing time was measured through operator operation; system reliability was verified through repeated testing; and the system's detection rate was tested by setting faults. Tests showed that the system's single-board testing time was reduced by more than half, and both reliability and detection rate were significantly improved. It met the system design requirements in terms of automation and versatility. Conclusion A powerful, high-performance, and easily expandable testing system was developed using a virtual instrument hardware and software platform, greatly improving production testing performance. Compared with traditional testing, virtual instrument testing has significant advantages and will undoubtedly see wider and more in-depth application.