At present, the display panels frequently used in control instruments mainly include LCD and LED. Among them, the LCD is more beautiful, power-saving, and flexible in display mode, but the price is relatively expensive. The most important thing is that its visibility is low, and the viewing angle is also Although the LED digital tube has a large power consumption, it has high brightness and is more conspicuous when used as an industrial site indication, and the price is low. Therefore, the use of LEDs as an indicator for industrial sites has a better price/performance ratio.
This paper introduces a design method of a universal intelligent digital display panel using LED digital tubes as display elements. The panel is based on the 80&TImes;160 & TImes;160 standard instrument chassis design, using the AT98C5X microcontroller as the controller. It can be used as a display unit for other instruments or as a stand-alone field display.
1 LED display panel functionThe LED universal intelligent display panel of this article is shown in Figure 1. The center of the panel is two rows of LED digital tubes, each with 4 positions. The upper row is red and the lower row is green. There are four LEDs on the left side of the panel and four key switches on the right side. Its displays and switches can be defined for different applications.
When the panel is used as a monitor for adjusting the meter, the upper row of LEDs can display the measured value and the lower row of LEDs can display the valve position feedback value. The LEDs on the left are used as working status indicators, from top to bottom, followed by high alarm, low alarm, automatic (bright) / manual, and instrument communication status indication. The buttons on the right are used for parameter setting and query operations. For convenience of description, the buttons are referred to as buttons 1 to 4 from top to bottom.
In the normal working state of the adjusting instrument, when the button 1 is pressed, the alarm upper limit value is displayed; when the button 2 is pressed, the alarm lower limit value is displayed; the button 3 is the valve opening degree manual/automatic switching. When set to the manual state, buttons 1 and 2 are used to remotely adjust the valve opening. Each time the valve position feedback value (the last digit of the green LED) is ±1. Button 4 is a function switching button.
In the instrument parameter setting state, button 1 is the loop mode selection parameter, red LED displays the current set value, green LED displays the sequence number of the set parameter; button 2 is the set bit parameter value
Add 1; button 3 can select the current bit of the setting parameter in the right loop mode, the currently set data bit is indicated by flashing; button 4 is to confirm the parameter setting, and press button 2 twice to switch the function.
When used as a stand-alone display unit, this display panel can be used as a multi-channel tour display alarm. During normal inspection, the upper row of LEDs shows the measured value and the lower row of LEDs shows the inspection loop number. The LED on the left shows the working state of the loop. From top to bottom, it is high alarm, low alarm, loop interruption, patrol (bright)/stop state. When a loop parameter exceeds the limit, the corresponding alarm indicator diode lights up.
The buttons on the right can be used to set parameters and queries. During normal operation (patrol inspection), button 2 is a function switch, and button 4 is a display mode switch. Press button 4 once to stop the inspection and maintain the current display status. In this state, press button 1 and button 2 to display the upper and lower alarm set values ​​of the circuit. Button 3 is used to cycle through the display circuit number. Each time the button is pressed, the circuit number is incremented by one. Press button 4 once. The system will enter the normal inspection state again.
2 hardware part design2.1 LED digital tube display circuit
The LED digital tube is formed by a plurality of light-emitting diodes arranged in a certain regularity. When a certain light-emitting diode is turned on, the corresponding segment is illuminated. According to the different connection modes of the internal light-emitting diodes, the LED digital tube can be divided into two types: a common anode and a common cathode. In this paper, the common anode display mode is adopted, and the segment code values ​​are from 0 to 9 in order: Ox0C0, OxF9, Ox0A4, Ox0BO, 0x9 9, 0x92, 0x82, 0x0F8, Ox80, 0x90.
The digital tube display driving method can be divided into dynamic (scanning) driving and static driving. The following are three design schemes:
(1) Static drive mode
In this mode, each LED digital tube displays its own character at the same time and remains unchanged until the next character is displayed. In this way, each digital tube should correspond to an 8-bit drive memory, and 8 digital tubes require a total of 64 drive lines, thus requiring more chips and a larger display panel area.
(2) Dynamic drive display with 8 bit selection lines
This is to connect all the same segment selection lines of the digital tube in parallel, and the digital tube position selection lines are alternately multiplexed in time division. At this time, only one digital tube is selected to emit light, and then the visual persistence feature of the human eye is used to achieve the simultaneous display effect. The display panel has 8 digital tubes, and only requires 8 bit drive lines and 8 segment drive lines. However, when the 8-bit cycle is displayed, the time of each digital tube is only 1/8 of the cycle time, which may cause the digital tube to flash.
(3) Dynamic display with 4-bit grouping
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