LED Segment Displays are made up of eight light-emitting diodes. A display device that is moved together by a certain pattern and permutation. Seven leds form seven, one LED that makes up the decimal point (the inherent time is also written in eight digital tubes). These segments are represented by the letter a, b, c, d, e, f, g, and dp. When the digital tube is specific and the voltage is added, these specific segments will be lit up to form the words "8" in our eyes. LED digital tubes have different points, such as bright and super bright, and have a different size of 0.5 and 1 inch. Small size commonly used digital tube display strokes of a light-emitting diode, and the big size of the digital tube is composed of two or more light-emitting diodes (leds), in general, a single light-emitting diode tube pressure drop is about 1.8 V, the electric current shall not exceed 30 ma. The anode of the light-emitting diode is linked together by the so-called coyang digital tube, which is connected by the cathode of the light-emitting diode to a digital tube. In total Yang digital tube, usually need to take positive public side, then need which Duan Liang, the corresponding period of the control pin is set to low level, in a total of Yin digital tube, need to connect power to public end, then need which Duan Liang, control of the corresponding period of pin is set to high level. The Numbers and characters shown in the LED digital tube are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. Understand these characteristics of leds, the programming is very important, because of the different types of digital tube, besides there are differences in their hardware circuit, programming methods are also different, when display character library of characters is not the same.
A, static display drivers:
The static driver is also known as the dc drive. A static drive is that each segment of a digital tube is driven by an I/O in a single chip. Static drive programming of the method is simple, high luminance, defect is occupied more than the I/O, such as the four digital tube display static are need 4 x 8 = 32 I/O mouth to drive, so I/O port of microcontroller is a great waste. So the application must be increased when the external drive circuit to drive, but also increased the complexity of the hardware circuit, so that when we design a product requires the selection of the choices. Do you want hardware simple, or do you want to save a single chip?
B, dynamic display drivers:
Dynamic display of digital tube is the most widely of single-chip microprocessor, a display mode dynamic driver is will all eight digital tube display stroke "a, b, c, d, e, f, g, dp" side of the same name together, in addition to each of the digital tube of public control greatly increase COM who called the road, who called the routing SCM I/O port control, when the microcontroller output glyph code, all digital tube to receive the same font code, but what exactly is the digital tube displays glyph, depends on the single chip microcomputer control of the COM the place called the road, only when a road called the strobe, output current will show us the font size. So all we need to do is to open the digital tube that needs to be displayed, and that bit will show the glyph, and the unselected digital tube will not be bright.
By rotating control of the COM end of each LED digital tube, the digital tube is controlled by turns, which is dynamic. In the process of display in turn, each digital tube light time is 1 ~ 2 ms, due to the phenomenon of persistence of vision and the afterglow effect of light-emitting diodes, despite the fact you digital tube is not lit at the same time, but as long as the scanning speed is fast enough, the impression is a set of stable display data, there will be no light flashes, and the static and dynamic display effect display is the same, can save a lot of I/O port, and lower power consumption.
In practice, digital tube display circuit also need to meet current limiting resistor (how to calculate the current limiting resistor, we follow-up to parse again), but we usually resistor than calculated value smaller, why? Because we in practice usually adopts the dynamic display method to drive the digital tube, digital tube so that each is not all the bright, but the flashing (we just couldn't see, don't think you're using a mobile phone camera to the dynamic display of digital tube photos look), natural brightness will drop, we have to reduce the size of the current limiting resistor to increase brightness.
In the dynamic display mode, we normally use triode to do the triode to switch. From experience, the NPN triode is used to drive the syn-cathode digital tube, and the PNP triode is used to drive the synyang digital tube, and the most commonly used is 8050 and 8550 (except for large digital tubes).
Finally a small question, you see the above introduction, do you really understand the digital tube? The question is, if I need to display a 4 at the moment, what does the "a b c d e f g dp" need to light up? Again, if it's a coinage digital tube, what is the display size of 4?