How to drive the segment code LCD screen?

[Summary description] In daily life, I see more segment code LCD screens, such as remote controls, refrigerators, electronic thermometers, displays on equipment, etc. The segment code screen is so widely used mainly because it has ordinary digital tubes. It has the characteristics of dot matrix LCD screen; it has fixed graphics, which is not only low cost but also beautiful. So, what is the liquid crystal driven by?

First of all, don't think that using a single-chip microcomputer to drive, just think that it is a DC-driven broken code screen. In fact, the segment code screen is driven by AC. You may often use a driver chip to play, such as HT1621, etc., However, there are some segmented screens with relatively few IO ports, or in the case of sufficient IO ports, it is too lazy to write the driver of the controller again. However, for the analog drive of IO, segment LCD has a prerequisite, that is, IO must be tri-state:

First of all: the important parameters of the segment code LCD screen: duty cycle, working voltage, bias ratio. These three parameters are very important and must be satisfied.

Secondly: the way of driving: we can know from the driving principle of LCD that only AC voltage can be added to the pixels of the LCD, and the contrast of the LCD display is calculated by the voltage value on the COM pin minus the voltage value on the SEG pin. It is decided that when this voltage difference is greater than the LCD saturation voltage, the pixel can be turned on, and when it is less than the LCD threshold voltage, the pixel can be turned off. The LCD-type MCU has automatically generated the LCD drive signal by the built-in LCD drive circuit. Therefore, only the I/O port can simulate the output of the driving signal, and then the LCD driving can be completed.

Then: the segment code LCD screen mainly has two kinds of pins, COM and SEG, which are similar to the digital tube, but the voltage difference must change alternately, for example: one moment is positive 3V, then the second moment must be reverse To 3V, pay attention, if you pass DC power to the segment LCD screen, it will not take long for the screen to be scrapped, so be careful.