What Are The Troubleshooting Techniques For Electromagnetic Interference On LCD Displays?

- Jun 01, 2018-


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When people use display devices, they are not only affected by the Earth's magnetic field, but also more or less affected by other devices drinking communication equipment. This is also called electromagnetic interference. When these devices are in operation, they become an electromagnetic source, forming a magnetic field around them and radiating electromagnetic waves outward. The size of the magnetic field and the intensity of the radiation are determined by the power of these devices.

LCD display


The LCD display is a pure input type or passive type for the entire system. The LCD display itself has no error correction function, that is, the liquid crystal display module can receive any signal that satisfies the operation timing relationship without the ability to judge the right and wrong, right and wrong. Both the wrong signal and the wrong data will generate wrong control instructions or wrong display patterns, resulting in an erroneous display effect. The primary task of eliminating interference is to find the source of the interference and the location of the interference, and then use effective methods to eliminate, weaken, or block and remedy the situation.

1. There is no display on the LCD screen and no contrast is adjusted. This phenomenon is because during the work of the whole machine, the power line or signal line of the LCD display is subjected to electromagnetic interference, which generates interference pulses, which causes the liquid crystal display module to be reset. The result of the reset is to initialize the module's internal registers and turn off the display. The recommended solution is to incorporate a stabilizing capacitor (10uF) and a filter capacitor (0.1uF or 0.01pF) between the power supply lines VDD, VSS closest to the liquid crystal display module if interference is applied to the power line. If interference is applied to the signal line, it is recommended to incorporate a filter capacitor between the signal line closest to the LCD display and VSS with a capacitance of 0.1uF or 0.01uF. The selection of the above capacitor values depends on the actual test results.

2. The screen produces incorrect characters or random points (data errors). Or the screen is panned, upside down, etc. Sometimes it cannot be recovered, only the screen can be cleared and re-written, and even need to be re-powered, the initialization register can be restored. This phenomenon is mostly due to interference applied to control signals such as /WR signal, /RD signal or E signal, or /CS signal. Interfering signals are more likely to produce erroneous waveforms on these signal lines, causing register parameters to be incorrectly modified and the display unit being miswritten. When the entire system is running, most programs only perform data writing operations on the partial display area. There are no other address write operations or repeated settings for some registers that are set only during initialization. Therefore, the above phenomenon occurs.