What is a segment LCD screen
Segment code LCD or segment code LCD screen is just a way for users of LCD screens to call a certain type of LCD screen, but in the LCD industry, it is generally called patterned LCD screen to distinguish it from the point. Array LCD screen, so segment LCD screen is not a very strict expression or classification.
The name of the segment code liquid crystal originated from the early application of the LCD screen, which was mainly used to replace the LED digital tube (it is composed of 7 pen segments, used to display the numbers 0-9), such as calculations Basically, the contents displayed on the devices, clocks and watches, etc. are numbers and relatively simple. Nowadays, non-dot-matrix LCD screens are generally collectively referred to as segment LCD screens.
The realization principle of segment code LCD screen
Each segment in the segment code screen is filled with a special liquid crystal. Under the action of the electric field, the arrangement direction of the crystal will be twisted, thus changing its light transmittance, so that the displayed content can be seen. The schematic diagram of this process is shown in Figure 3.
To make the crystal twist, the voltage difference between the electrodes must be greater than a certain threshold before the content can be displayed. Usually LCD segment code screen has three parameters: working voltage, Duty (corresponding to the number of COM) and BIAS (bias voltage, corresponding to the threshold), for example, 3.3V, 1/4 Duty, 1/3 BIAS means that the operating voltage of the LCD is 3.3V , There are 4 COMs, and the threshold is about 1.1V (3.3/3=1.1). In actual use, in order to ensure a good display effect, the voltage difference applied to the two ends of the electrode is usually close to the working voltage of the LCD; if it is not displayed, the voltage difference applied to the two ends of the electrode is usually close to oV. It is important to note that the liquid molecules need to be driven by AC signals. Do not apply DC voltage to both ends of the electrodes for a long time. Otherwise, the electrochemical characteristics of the liquid crystal molecules will be affected and the display effect will be blurred. The consequence of the reduced life span is irreversible.
After understanding the above principles, when we want to light a certain segment, we only need to ensure that the voltage difference between the two ends of the electrode is 3.3V (for example, COM1=3.3V, SEG1=0V), and the interval is appropriate. The voltage reversal output of the two poles<(such as COM1=0V, SEG1=3.3V); when a certain segment is not lit, only need to ensure that the voltage difference applied to the two ends of the electrode is OV (such as COM1=3.3V, SEG1= 3.3V), and at a suitable interval, the voltage of the two poles is inverted and output (for example, COM1=ov, SEG1=oV).
To achieve such an operation, an MCU with fast main frequency, accurate timing and low power consumption is required. The author once used Silicon Labs' EFM8SB10F8 microcontroller to successfully implement the operation of the battery indicator segment screen. EFM8SB10F8 can reach up to 25MHz main frequency, which is fully capable of fast flipping I0 operation; 16-bit Timer can accurately maintain the appropriate time interval, so that the segment screen achieves a good display effect; the MCU has a built-in 24MHz high-precision oscillator, The accuracy can reach ±2%, which provides a precise reference for the Timer, and at the same time, it can save the external crystal oscillator and reduce the cost of the product; it can reach as low as 0.6uA during sleep, which greatly extends the standby time of the product.
On the hardware, the circuit design has also become very simple to install, see Figure 4 for details; on the software, the core code for driving the segment code screen is not complicated, see Figure 5 for details. When in use, you only need to call the API function of the driver code in the Timer interrupt function to light up the segment code screen. If the color of the displayed image is relatively light, the time interval during which the Timer is interrupted can be appropriately extended to achieve a better display effect.
Segment code LCD screen application
Instruments and meters: gas meter, water meter, bus system, tanker counting display, office equipment: fax machine, punch card machine, survey machine, access control system, communication equipment: various IC card phones, Internet phones, IP phones
Banking system: POS machine
Tax system: tax control machine
Medical equipment: physiological monitors and various health equipment
Industrial control equipment: automatic control
Various man-machine interfaces, handheld devices, etc.
Advantages and disadvantages of segment code LCD screen
The advantages of the segment code LCD screen: low requirements for the main control chip, simple software, low cost of controlling the LCD screen and main control.
Disadvantages of segment code LCD screen: the text cannot be changed
