The method of driving segment LED (digital tube) with IO port is relatively clear to everyone, but the method of directly driving segment LCD with IO port is relatively more complicated. I searched the Internet for the method of driving the segment LCD with the IO port of the single-chip microcomputer. Most of the information is not clear enough and specific, and simple problems are complicated. Now, based on the LCD display principle, combined with relevant information on the Internet, I will briefly introduce how to use a single-chip microcomputer to drive the segment code LCD liquid crystal display:
1. The display principle of LCD and LED is different: LED emits light with positive voltage, while LCD must alternately add positive and reverse voltage to display continuously (you can do an experiment, if a constant voltage is applied to a segment of the LCD, This segment will be displayed, but it will not be displayed immediately, and a constant voltage will be applied for a long time, which will accelerate the aging and damage of the LCD)
2. What do I often hear about 1/2bias and 1/3bias LCD? For 1/2bias LCD, if the display voltage of the LCD is 3V, then 1/2bias is 1.5V, that is to say, when the voltage of ±3V is applied, the LCD will display; when the voltage of ±1.5V and below is applied, there is no display.
3. The IO port of ordinary single-chip microcomputer can not directly output half-high level (1.5V), but it can be realized with equal pull-up and pull-down resistors. When the IO port is set as input (high resistance), due to the partial pressure of the pull-up and pull-down resistors, Generate a half-high level (1.5V)
After knowing the above 3 points, it is not difficult to drive LCD dynamically. For a 48 segment LCD (4 COM, 8 SEG, display voltage 3V, 1/2 bias), the driving method is as follows:
1. The four COMs are scanned alternately, and each COM performs a voltage alternating method during two adjacent scans.
2. If a certain COM is scanned, the COM will output 3V (0V):
The SEG output connected to this COM is opposite to COM, ΔV=±3V, then this connection will light up;
The SEG output connected to this COM is the same as COM, ΔV=0, then the connected point is not bright.
3. For other COMs that are not scanned, the IO port of the single-chip microcomputer is input, which generates 1/2 bias (1.5V). Regardless of the value of SEG, ΔV<±1.5v, so="" the="" light="" does="" not="" light="">
