Single-chip drive LED, digital tube, lcd display

1, what is light-emitting diode

Light-emitting diodes are everywhere in everyday appliances, it can shine, there are red, green and yellow, etc. Diameter 3mm, 5mm and 2× 5mm rectangular. Like ordinary diodes, LEDs are also made of semiconductor materials and also have the property of unidirectional conduction, that is, only the polarity of the pair can be illuminated. The LED symbol has two more arrows than the normal diode, indicating that it can emit light. Usually LEDs are used to indicate the operating state of the circuit. It consumes much less power than a small bulb and has a much longer life. LEDs can also be used to form electronic displays. The display on the stock exchange is composed of LED arrays, just because the colors are composed of red, green and blue, and the blue LEDs have not been large before. Produced, so the general electronic display can not display true color. The light-emitting color of a light-emitting diode is generally the same as its own color. However, in recent years, a transparent color light-emitting tube has appeared, which can also emit light of red, yellow, green, etc., and can only be known when power is supplied. There are experimental methods and visual methods for distinguishing the positive and negative electrodes of a light-emitting diode. The experimental method is to check if it can be illuminated, if it is not the polarity is wrong or the LED is damaged. Note that the light-emitting diode is a current-type device. Although it can be illuminated after being directly connected to the voltage of 3V at both ends, it is easy to be damaged. In actual use, the current-limiting resistor must be connected in series. The working current is generally 1mA depending on the model. To 3OmA. In addition, since the on-voltage of the light-emitting diode is generally 1.7V or more, a 1.5V battery cannot illuminate the light-emitting diode. Similarly, the general multimeter's R× 1 file to R× 1K file can not test the LED, and R× 10K file can use some 15V battery to light some of the LED. Using the eyes to observe the LEDs, you can find that the two internal electrodes are large and small. In general, one with a smaller electrode and a shorter one is the positive electrode of the LED, and the larger one is its negative. In the case of a newly purchased LED, the longer one of the pins is the positive pole. This is the LED: The symbol is: . Let's take a look at this circuit. When switch J1 is turned on, no current flows through the LED, and the LED does not illuminate. When the switch J1 is closed, a current flows through the light emitting diode, and the light emitting diode lights up.

Introduction to LCD

At present, the mainstream LCD (liquid crystal display) in the market is divided into the following categories: TN (twisted array type), STN (super twisted array type), DSTN (double layer super twisted) Array), HPA (High Performance Addressing or Fast DSTN), TFT (Thin FET), etc. Due to cost factors, most of the current small appliances use TN-type monochrome liquid crystal displays. The principle is to pour liquid crystal into two planes with fine grooves. The grooves on the two planes are perpendicular to each other (intersecting at 90 & deg;), that is, if the molecules on one plane are arranged in a north-south direction, the molecules on the other plane are arranged east-west, and the molecules between the two planes Forced into a 90° twisted state. Since the light propagates in the direction in which the molecules are arranged, the light is also twisted by 90° when passing through the liquid crystal. When a voltage is applied to the liquid crystal, the molecules are re-arranged vertically so that the light can be directed out without any twisting. The LCD is made up of two mutually perpendicular polarizing filters, so under normal circumstances all light that attempts to penetrate should be blocked. However, since the two filters are filled with twisted liquid crystals, after the light passes through the first filter, it is twisted by the liquid crystal molecules by 90° and finally passes through the second filter. On the other hand, if a voltage is applied to the liquid crystal, the molecules are rearranged and completely parallel, so that the light is no longer twisted, so it is just blocked by the second filter. In short, power is applied to block light, and light is emitted without power. The LCD model can be thought of as a capacitor, with one electrode connected to the common plate and the other connected to the character segment. The LCD is controlled by the rms value of the voltage. When the voltage applied to the LCD is zero, the LCD is transparent. When the voltage applied to the character segment and the common pole is greater than the threshold voltage of the LCD, the character segment is displayed. If the LCD is driven by DC, it will cause permanent damage to the display unit. In order to prevent the irreversible electrochemical reaction from damaging the LCD, the voltage applied to all segments must be periodically flipped so that the average voltage applied to the segment is zero. In order to save the MCU I/O line, the LCD is driven by multiplexing.

1. What is a digital tube LED Many electronic products have a beating digital to indicate the working state of the electrical appliance. In fact, the digital display of the digital tube is composed of eight light-emitting diodes. The segment is illuminated by applying a suitable voltage to each segment. LED digital has two kinds of common yang and common yin, the positive pole of these LED light-emitting diodes are connected to one piece (generally, they are spelled into one 8 characters plus one decimal point) and as a pin, it is called yangyang, on the contrary, it is called Commonly, this pin is connected to VCC and GND respectively when applied. Putting more than one of these 8 characters together becomes a multi-digit digital tube. The shape is as follows: The common anode type is that the positive poles of the eight luminous tubes are connected together as one lead. The internal structure of the common cathode type is that the cathodes of the seven LEDs are connected together as a lead. Pins A~G are used to display numbers, strokes of characters, (dp shows decimal point), and each segment controls the brightness of A~G~dp. 1. COM pin is connected as a common terminal. 2. Analysis Please indicate how to display the 0~9 ten digits, how to set the switch to be closed with “1”, open with ”0” indicates that the switch setting status is as follows: ":

J1 J2 J3 J4 J5 J6 J7 Display 1 1 1 1 1 1 0 0 0 1 1 0 0 0 0 1 1 1 0 1 1 1 1 2 1 1 1 1 0 0 1 3 0 1 1 1 1 1 1 4 1 0 1 1 0 1 1 5 0 0 1 1 1 1 1 6 1 1 1 0 0 0 0 7 1 1 1 1 1 1 1 8 1 1 1 1 0 1 1 9