In a variety of electronic control equipment, digital display has become an indispensable and important link. The electronic devices and corresponding driving circuits used for digital display are called digital displays.
Commonly used digital displays include glow digital tube displays, fluorescent digital tube displays, projection displays and edge light displays. Some novel display devices, such as field-effect light-emitting elements, electron beam display tubes, solid-state displays and liquid crystal displays, are also becoming more and more widely used.
Glow digital tube
The glow digital tube is made using the principle of glow discharge, and the shape is no different from that of ordinary electron tubes. A glass tube filled with neon gas is fitted with a common anode and ten cathodes, each of which is bent into a wire by wire. 0、1、2… The shape of ten digits such as 9 overlaps each other, leaving a small gap in between. The distance between each cathode and anode is arranged according to the number of strokes of each number.
Projection displays
The disadvantage of glow digital tube displays is that they require a higher DC voltage. In recent years, some display devices that operate at low voltages have been produced one after another. Projection displays are one of them. It utilizes the working principle of the slide show and consists of 12 groups of projection systems. Each projection system consists of an optical system (condenser and magnifying glass), a light source (small lamp), a digital or symbolic film to be displayed, and a projection screen for imaging. It has 12 small indicator bulbs on the back bottom panel, and a small darkroom with a blackout compartment between them. On the other side is a frosted glass projection screen for display. Between the bead base plate and the projection screen, there is a condenser corresponding to each lamp, a film of displayed numbers or symbols, and a magnifying glass. In order to display a certain number, it is only necessary to turn on the corresponding indicator light: the light is illuminated by a condenser onto the translucent film, magnified by a magnifying glass and projected onto a frosted glass projection screen, so that the number or symbol can be clearly displayed.
Compared with other displays, in addition to low-voltage power supply, projection displays also have the advantages of large field of view, clear and beautiful display, all words reflected on the same plane, and durability. Its main disadvantage is that the small lamp is full of large working current (6-8 volt small indicator, working current is more than 150 mA), and the required power supply capacity is also larger. Moreover, due to the large hot state resistance and small cold resistance of tungsten filament bulb, the starting current is several times larger than the normal working current at the moment of ignition of the bulb, which is easy to cause power overload and even burn out the transistors in the driving circuit.
Edge-lit display
The edge-lit display, also known as the edge-emitting display, is another low-voltage display device that uses the light guide characteristics of the edge of plexiglass. Its structure is much simpler than that of a projection display, with the main body being a piece of plexiglass engraved with numbers and a small lamp saturated by specially made leads at both ends. As soon as a light bulb is lit, the edge of the lettering on the corresponding plexiglass sheet is illuminated. Plexiglass is colorless and transparent, and when stacked, the pieces do not affect each other. The driving circuit of the edge-lit display is basically the same as that of the projection display.
Fluorescent digital tubes
Fluorescent digital tube is also a new type of display device. Its outstanding advantages are low working voltage, small driving current, long life and clear display. This digital tube, like an electron tube, has a hot cathode and a gate. However, the anode is divided into several independent fragments (domestic fluorescent digital tubes have six-segment, seven-segment, eight-segment and other types), which are composed of different arrangements and combinations. 0, 1, 2...9 ten numbers. The surface of the anode is coated with a luminescent layer of fluorescent substances, which can emit light by electron excitation. It is no longer oxidized before being transferred to the plating tank. Anodizing etching is carried out in a sulfuric acid solution at a concentration of 30%. The plating part is connected to the anode, and the lead plate is used as the cathode, except for the inner hole, the cathode area should be more than 4 times larger than the anode area.
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