Segment code LCD or segment code LCD screen, but LCD screen users for a certain type of LCD screen is a name, but in the LCD industry, generally referred to as the pattern of the LCD screen, so as to distinguish between the point Formation of the LCD screen, so paragraph code LCD screen is not a very strict statement or classification.
The name of the segment code LCD is originated from the beginning of the application of the early LCD display. It is mainly used to replace the LED digital tube (it is composed of 7 segments, used to display the number 0~9), such as calculation The displays, clocks, and so on, are basically numbers, and they are relatively simple. Now, non-lattice LCD screens are generally referred to as segment code LCD screens.
The advantage of segment code LCD screen is that it requires low requirements for the main control chip, simple software, low cost for controlling the LCD screen and main control.
Disadvantages of segment code LCD screen: It is text that cannot be changed
How does the segment code LCD work?TN-type LCD screens are usually fully transparent, semi-transparent, and reflective. The liquid crystal does not emit light automatically, and an external light source is needed. The light source of the transmissive liquid crystal is behind the liquid crystal; the light source of the reflective liquid crystal comes from the front of the liquid crystal and is reflected by the polarizer of the liquid crystal panel to the eyes of the viewer; the translucent liquid crystal is interposed between the two, both from the rear of the liquid crystal. The light also has reflected front light. Therefore, a full-type liquid crystal needs to use a backlight, a reflective type does not require a backlight, and a semi-permeable type of liquid crystal can use a backlight or not. LCD screens that do not use a backlight are not visible in the dark.
Material: TN, HTN, STN, BTN (VATN), FSTN and other materials.
Display mode: positive display, negative display.
Polaroid types: fully transparent, semi-permeable, reflective.
Driving conditions: related to the selected driver chip, such as the commonly used HT1621 chip, its duty cycle 1/4DUTY, bias ratio 1/3BIAS.
Connection method: metal pin connection, conductive strip connection, hot press connection, FPC cord connection.
Observation angle: 6 o'clock viewing angle, 12 o'clock viewing angle.
Operating voltage: Normally set working voltage is between 3~5V, LCD power consumption is about 10μA.
Working temperature: The temperature range can be set according to the working environment of the LCD. The widest temperature is about -35°C~85°C.
Segment code LCD screen principle
Each section in the segment screen is filled with a special liquid crystal. Under the action of the electric field, the orientation of the crystals will be reversed, thus changing their translucency, so that the displayed contents can be seen. The schematic diagram of this process is shown in Figure 3.
Figure 3: LCD display principle
To make the crystal twist, the voltage difference across the electrodes must be greater than a certain threshold in order to display the content. Generally, the LCD segment code screen has three parameters: working voltage, Duty (corresponding to COM number) and BIAS (bias, corresponding threshold). For example, 3.3V, 1/4 Duty, and 1/3 BIAS indicate that the working voltage of the LCD is 3.3V. There are 4 COMs and the threshold is approximately 1.1V (3.3/3=1.1). In actual use, in order to ensure a good display effect, the voltage difference applied to both ends of the electrode is usually close to the working voltage of the LCD; if it is not displayed, the voltage difference applied to both ends of the electrode is usually close to 0V. It is necessary to pay special attention to the fact that the liquid crystal molecules need to be driven by alternating current signals. Do not add DC voltage to the ends of the electrodes for a long time. Otherwise, the electrochemistry characteristics of the liquid crystal molecules will be affected and the display effect will be blurred. The consequences of the reduction are irreversible and destructive.
After understanding the above principles, when we want to light a certain segment, we only need to ensure that the voltage difference across the electrodes is 3.3V (such as COM1=3.3V, SEG1=0V), and the appropriate time interval will be Two-pole voltage inverting output (such as COM1=0V, SEG1=3.3V); when not lighting a certain segment, only need to ensure that the voltage difference between the two ends of the electrode is 0V (eg, COM1=3.3V, SEG1=3.3 V), and at appropriate intervals, invert the voltage of these two poles (eg COM1=0V, SEG1=0V).
To achieve this kind of operation, an MCU with fast main frequency, accurate timing, and low power consumption is required. I have used Silicon Labs's EFM8SB10F8 microcontroller to successfully implement the power indicator segment screen operation. EFM8SB10F8 up to 25MHz frequency, fully capable of rapid flip IO operation; 16-bit Timer can accurately maintain the appropriate time interval, so that segmentation screen to achieve a good display; The MCU built-in 24MHz high-precision oscillator, Accuracy can reach ± ​​2%, providing a precise reference for Timer, but also can save the external crystal, reducing product cost; the lowest possible sleep up to 0.6μA, greatly extending the product's standby time.
On the hardware, the design of the circuit has also become very simple, as shown in Figure 4. In software, the core code of the segment code screen is not complicated. See Figure 5 for details. When using, only need to call the API function of the driver code in the Timer interrupt function to light the segment code screen. If the color of the displayed image is relatively light, the time interval during which the Timer generates the interrupt can be appropriately extended to achieve a better display effect.
Instruments, meters: gas meters, water meters, bus systems, fuel dispensers, count display, office equipment: fax machines, punch machines, attendance machines, access control systems, communications equipment: all kinds of IC card phones, Internet phones, IP phones
Banking system: POS machine
Tax System: Tax Control Machine
Medical Equipment: Physiological Monitors and Health Care Devices
Industrial Control Equipment: Automation Control
Various human-machine interfaces, handheld devices, etc.
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