Displays to be used in display computers for vehicles and machines in critical environments shall be possible to inspect regarding pixel defects. The main part of the goal was to realize a test equipment so that different colours can be visualized on displays of different resolutions and interfaces, with a minimum startup time. The inspection of the displays will be visual.
One pixel is consisting of three sub-pixels: red, green and blue, each controlled by a Thin Film Transistor (TFT). If some TFTs are broken, different types of pixel defects occur. There is an ISO standard defining classes for how many defects of each type that can exist on a display before it should be replaced by the supplier. But other limits can be agreed between supplier and customer. To be able to see the different types of pixel faults, 5 different colours should be shown on the display: red, green, blue, black and white.
A list was supplied containing 10 different models of display elements for which tests should be possible. They were thoroughly analyzed regarding their technical data for resolution and interfaces for backlight and video signals. The displays are of 3 different resolutions. 5 displays have backlight of the older technology Cold Cathode Fluorescent Lamps (CCFL) which means neon light from tubes, while 5 have the later technology Light Emitting Diodes (LED). 2 of the displays receive the video signals in parallel, while 8 receive them via Low Voltage Differential Signaling (LVDS). The LVDS connector showed to have a special pin configuration for 2 of the 8 LVDS displays. This was the most important discovery, because if the standard LVDS cable would have been used from the carrier board, the displays would probably have been damaged. Because of these differences different types of boards and cables had to be used, both standard parts and modified, to be able to supply the different display models with backlight and video signals.
To achieve the main part of the goal an existing display computer was modified and used as the base platform for a prototype test equipment. All signaling to the display had to be generated by the FPGA instead of the CPU module. The FPGA project was written in VHDL language. The project included six different modules of which some were written from scratch, some were reused and some were partly reused from an already existing FPGA project. Display resolution is set with a jumper and the 5 colours are visualized in a loop, using a push button.
2012. , 33 p.