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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Liquid crystal indicators. Reference data
Encyclopedia of radio electronics and electrical engineering / Reference materials ИЖЦ71-5/7; ИЖЦ72-5/7 Digital five-digit indicators IZhTs71-5/7 and IZhTs72-5/7 with a decimal point in each digit and a built-in microcircuit control unit are designed to display digital information in equipment installed outdoors (gas, liquid fuel, electricity meters, outdoor thermometers, etc.). P.). Structurally, the indicator is generally two flat thin glass plates hermetically glued along the perimeter with a small gap filled with a cold-resistant liquid crystal substance. The operation of the indicator is based on the twist effect in liquid crystals, for which two polaroids are provided in the design - two thin films that have the property of polarizing the light passing through them. The twist effect is a phenomenon of rotation of the plane of polarization of polarized light by a thin (about 20 microns) layer of liquid crystals, which disappears when an electric field is applied to this layer. The planes of light polarization provided by each of the polaroids are mutually perpendicular (they are called crossed). Generally speaking, a system of crossed polaroids does not transmit light, but if a layer of liquid crystals is placed between them, which, in turn, rotates the plane of polarization of light by 90 degrees, the system becomes transparent. Under the influence of an electric field on any part of the layer of liquid crystals, they lose the ability to rotate the plane of polarization of light and the transmission of light stops. Visually, this is perceived as the appearance of a dark, opaque area on a light background. The electric field must be alternating, otherwise an electrolytic process occurs in the layer of liquid crystals, leading to a sharp reduction in their service life. The IZhTs71-5/7 indicator is designed to work on reflected light, for which a mirror coating is applied to the back of the device. The IZhTs72-5/7 indicator is translucent and works through the light, but it can be switched to a reflective mode if a mirror plate is installed behind the device close to it. The device is equipped with twenty hard tinned square leads for external signals. The appearance of the indicator is shown in fig. 1. Mass of the device - no more than 60 g.
The pinout of the indicator is shown in Table 1.
The control unit of the indicator is built on the basis of a 1835-channel chip KB1ID4-XNUMX of the CMOS structure. As mentioned, the indicator uses a cold-resistant liquid-crystal substance that allows normal operation of the device up to a temperature of -30°C. At temperatures below -30°C, the time for changing information on the display noticeably increases. The required speed of the indicator at a temperature in the range of -30 ... -40 ° C is provided by a special heater powered by current. This device is made on the basis of cermet, has its own conclusions and is supplied separately from the indicator. In order to protect the polaroid of the indicator, placed on its front side, from damage during storage and installation, the display is covered with a protective film at the factory. Before using the device, the protective film must be removed. The first three letters of the name of the indicator mean the Liquid Crystal Digital Indicator, the number 71 is the serial number of the development, the number 5 is the number of digits, and 7 is the number of image elements in the digit. The main technical characteristics of the indicator at Tacr.av = 25°C
Operating limits
The indicator receives external information via the eight-bit line DO - D7 using the CWR clock signal. After the information about all image elements is entered into the input register of the control unit (within five clock pulses of writing a byte), a WR pulse arrives at the "Overwrite" input, which rewrites information from the input register to the storage register. Timing diagrams illustrating the operation of the control unit are shown in fig. 2.
From the storage register, information enters the output shapers responsible for the on or off state of the elements of the first frame in accordance with the received external information. The new information of the second frame follows the same path and enters the scoreboard. Thus, we can say that the control unit has a memory of two pages - one stores information about the received frame, and the other at this time writes information about the next frame. The formation of an alternating (without a constant component) exciting voltage indicator occurs according to the COSL signals. The "Invert output information" function provides the user with the ability to supply information to the indicator both in direct form (when a high level at the information input corresponds to the switched on element of the scoreboard), and in inverse form (when the scoreboard element is turned on by a low input level). Direct introduction corresponds to a low level at the input Ip, and inverse - to a high level. "Relay signal output" when using a single indicator is left free. If it is necessary to increase the number of digits of the indication, a second similar indicator is installed nearby, and the pin. 20 of the first is connected to an external control unit. For indicators of this and other types capable of operating in transmitted light, special backlight modules with incandescent lamps are produced. Liquid crystal indicators of all types should be protected from prolonged exposure to direct sunlight - this can lead to irreversible destruction of liquid crystals. For the same reason, indicators should be protected from static electricity and overheating when soldering. IZHTS35-6/7 Six-digit digital indicators IZhTs35-6/7 are designed to display output information in self-powered pocket electronic medical equipment. In addition to six digital digits, there are six mnemonic elements on the scoreboard. The indicator is based on the twist effect. The device is designed to work in reflected light; image color - black, background - light gray. Control mode - static. The case is glass, flat (Fig. 3). The conclusions are transparent (conditionally shown in black in the figure) conductive strips - pads deposited on the glass of the case from the front side. The indicator is connected to the device circuits using two contact rubber combs, made up of alternating conductive and non-conductive sections.
Contact pads (their total number is 52) are placed in two rows, one on each long side of the case. If you look at the instrument panel from the front (the protrusion-key on the case should be on the left), then the bottom row will be the first, the top - the second. The numbering of the conclusions in the first row (from 1st to 26th) goes from left to right, and in the second (from 27th to 52nd) - from right to left. The pinout of the IZhTs35-6 / 7 indicator (the numbering of the digits on the display increases from left to right): pin. pin.
Indicator weight - no more than 2 g. The main technical characteristics of the indicator at Tacr.av = 25°C
Operating limits
The main parameter of all liquid crystal indicators, which reflects the quality of their work, is the contrast of the sign in relation to the background. Contrast K is defined as the ratio of the intensity values of the light coming out of the indicator in the initial and excited states. This parameter is measured using a special optical setup, which is based on a microscope with a built-in photoelectronic current multiplier at the output. The contrast is calculated as a percentage by the formula: K = (IF - I3) 100/ Iph, where Iph - background current - output photocurrent of the electron multiplier with the indicator off; l3 - sign current - the output photocurrent of the multiplier when the indicator is excited by the nominal control voltage (if the sign image is darker than the background of the display). The contrast is sometimes expressed in relative units; in these cases, the factor 100 drops out of the specified formula. IZHTS4-12/7 Twelve-row digital twist-effect indicators IZhTs4-12/7 operate on light reflection and are designed to display information in multifunctional telephones and payphones. Image color - black, background - light gray. The indicator's operating mode is multiplex. In addition to digital digits, seven words are placed in a row on the instrument panel, each controlled in the same way as a separate element of the digit. The device is able to work normally at low ambient temperatures - up to -30°C. This is achieved by using a frost-resistant liquid crystal material. The indicator housing is glass flat (Fig. 4); conclusions - rigid, tinned. Weight - no more than 80 g.
If you place the device with the front side towards you and the leads down, then the pin will be the far left. 1, and on the far right - pin. 39. The numbering of the digits on the scoreboard increases from left to right. The pinout of the indicator is shown in Table. 2 (digital digits) and table. 3 (words).
Main technical characteristics at Tacr.av = 25°С
As mentioned, the indicator is designed for multiplex control mode with a clock ratio of 1:3. This means that after each time cycle of the excited state of one or another image element, three cycles of control voltage absence follow. As a result of the inertia of the liquid crystal substance, the brightness contrast does not have time to noticeably change during this time. Then the process is repeated with the same clock ratio. ИЖВ74-160Х16; ИЖВ76-160Х16 Alphanumeric matrix indicators IZHV74-160x16 and IZHV76-160X16 with a built-in control unit are designed to display alphanumeric information in portable measuring and computing equipment. Indicators IZHV74-160X16 work for light reflection, and IZHV76-160X16 - for transmission. The operation of indicators is based on the twist effect. Included image elements appear black on a light gray background.
On the instrument panel there are two lines 149,1 mm long, consisting of 32 familiarity spaces in each. The familiarity has a matrix structure of 7X5 rectangular elements. The dimensions of the element are 0,8x0,6 mm, the dimensions of the familiarity are 6,2x3,4 mm. Under each of the lines is the so-called cursor line, which consists of a single row of elements of the same size. These lines allow you to form moving markers-indicators of one or another character in a line. The case of indicators is glass flat (Fig. 5, a). The outputs for receiving control signals are made in the form of printed conductive foil tracks on two thin (about 0,1 mm thick) flexible polyimide tapes. On one tape - 12 conclusions (this group is designated X1), on the other - 21 (X2). Pin pitch - 1,25 mm; pin width - 0,6 mm. The conclusions are formed on the extreme edge of the polyimide tapes to the right of the case (if you look at the front side of the indicator). The shape of the tapes is such that the bottom is a tape with the leads of the X2 group, with their conductive side facing back, and the top is the tape with the leads of the X1 group facing forward. On fig. 5,6 shows a large arrangement of the elements of the familiarity of the indicator. The dimensions of the indication field are 149,1X16,1 mm. Indicator weight - 100 g. In the name of the device, the letter B denotes an alphanumeric group of indicators in the accepted system, the numbers 74 or 76 are the serial numbers of the development, and 160 and 16 indicate the number of columns and rows, respectively, forming the information field of the indicator. Each image element is formed at the intersection of its row and column. The pinout of the indicator is shown in Table. four.
Main technical characteristics at Tacr.av = 25 °С
Operating limits
The built-in logical block for controlling the rows and columns of the indicator is made on open-frame microcircuits KB1835ID1-4 of the CMOS structure. Each chip is capable of serving 40 channels (rows or columns). Timing diagrams illustrating the operation of the block are shown in fig. 6.
The introduction of information into the input register occurs in parallel-serially through the input eight-bit line D0 - D7 and is clocked by the CWR signal. For 20 cycles, the input information about all 160 elements of one line is recorded. On the edge of the WR pulse, the input information is rewritten in parallel from the input register to the output. The same signal applied to the line control node starts scanning the next line from its beginning. The writing process proceeds from left to right along the row and from top to bottom in the columns. The leading bit D0 in each byte is displayed on the left. Frame synchronization (setting the start of the sweep to the upper left corner of the indication field before the frame is transmitted) is provided by SR pulses applied to the indicator from an external control unit. The formation of an alternating excitation voltage of the indicator is controlled by the signal COSL In addition, the column control node must be signaled In. If the input In is low, then the high level at the inputs D0 - D7 will correspond to included image elements, and the low level will correspond to non-included ones. At a high level at the input In, on the contrary, a high level at the inputs D0 - D7 corresponds to the non-activation of the elements, and a low level corresponds to the inclusion. A six-level optimized mode is used to drive the display elements. The output circuits of the row control node are powered by two pairs of inputs of the X1 group - U1, U2, U5, U6, and for the column control node - U1, U3, U4, U6 of the X2 group. The supply voltage is from Upit to -10 V. These signals are generated either by an external control unit or a set of external resistive dividers. The principle of calculating the values U1 - U6 of the supply voltage is described in more detail below, when describing the indicators IZHG96-240X80 and IZHG97-240X80. ИЖГ96-240Х80; ИЖГ97-240Х80 Graphic indicators IZHG96-240X80 and IZHG97-240X80 with a built-in control unit are designed to display alphabetic, numeric and graphic information in portable measuring and computing equipment. Indicator IZHG96-240X80 is reflective, and IZHG97-240X80 is translucent. The device is based on the supertwist effect. This term, which has been used in the scientific and technical literature for the past few years, refers to the same twist effect, but implemented in higher-tech structures with more advanced materials. Supertwist effect provides higher image contrast and faster performance. The color of the included elements on the display of the devices in question is dark blue on a light yellow-green background. The dimensions of the display board are 131,9x43,9 mm.
The case is flat glass (Fig. 7, a). The conclusions are made in the form of printed foil tracks on two flexible polyimide tapes. There are 12 leads on one tape (X1 group), on the other - 21 (X2). Pin pitch 1,25 mm, pin width 0,6 mm. The tapes are displayed on the right side of the indicator (if you look at the front side of its display), and at the bottom there is a tape with the conclusions of the X2 group with the conductive side back, and on top there is a tape with the X1 group with the conductive side forward. On fig. 7b shows the relative position and size of the image elements on the indicator board. Image elements - square dots - are evenly distributed on the field. The dimensions of one element are 0,45x0,45 mm. Indicator weight - no more than 80 g. The letter G in the name of the indicator indicates the method of displaying information - graphic, the numbers 96 and 97 are the serial numbers of the development, and 240 and 80 are the numbers of columns and lines, respectively, forming the information field of the device. According to the pinout, the indicators IZHG96-240X80 and IZHG97-240x80 are similar to IZHV74-160x16 and IZHV76-160X16 (see Table 4). Main technical characteristics at Tacr.av=25°С
Operating limits
The built-in logical control unit for rows and columns is made on open-frame microcircuits KB1835ID1-4. The general principle of managing rows and columns is the same as that of IZHV74-160X16. The output circuits of the row control unit are also fed, but the supply voltage limits are somewhat wider - from Upit to -12 V. Diagrams of signals generated by control nodes in rows and columns and applied to indicator outputs are shown in fig. 8.
The values U1-U6 of the power supply voltage of the row and column control nodes (formed by an external unit) must satisfy the following relationships: U1≤Upit; U2=U1-U0; U3=U1-2U0; U4=U1-(a-1)U0; U5=U1-U0; U6≥-12 V, where Upit=5±0,5 V; a=√n-9 - optimization coefficient; n=80 - the degree of multiplexing (or, otherwise, the duty cycle of scanning lines); U0 - initial voltage, determined by the individual characteristics of the indicator and lying within 1 ... 2 V; typical value - 1,3 V. The equality of the differences U1-U2=U2-U3= U4-U5=U5-U6=U0 must be ensured with an accuracy of at least ±1%. The accuracy of setting the optimization coefficient should be within ±5%. Everything related to the choice of supply voltage values for the output circuits of row and column control units equally applies to indicators IZHV74-1 60x 16 and IZHV76-160x 16.
On fig. 9 shows the dependence of the intrinsic brightness contrast on the voltage U1-U6. On fig. 10 - 12 shows the dependences of the current consumed by the indicator on various parameters - on the voltage U1-U6, on the frequency fcwr and fcosi. respectively. Author: A.Yushin, Moscow
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