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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Two versions of the Nokia 5110 LCD radiation statistic meter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology Among the whole variety of devices that measure the level of radiation, it is difficult to find one that would show not only the current level, but also the dynamics of its change over the course of an hour, day, month. This information would be useful in assessing the real radiation hazard. The proposed devices to some extent fill this gap. In the course of their development and implementation, the author had to solve the problem of organizing the interaction of the LCD indicator from the Nokia 5110 mobile phone, chosen as a means of displaying the measurement results, with a microcontroller of the PIC family, and not only with Arduino modules, for which there are corresponding libraries on the Internet [1]. Two devices were created, shown in the photograph of Fig. 1. The one on the left in the picture works in conjunction with the radiation meter-indicator previously developed by the author [2], which is visible in the background. The second device is able to work independently, since it contains a miniature Geiger-Muller counter SBM-21 [3] and all the elements necessary for the operation of this counter.
The statistical indicator-attachment is built on the PIC12F683-I/P microcontroller [4], which performs all the necessary calculations and controls the LCD from the Nokia 5110 phone. The device performs statistical processing of the Geiger-Muller counter pulses received from the meter-indicator for a fixed time interval. The duration of this interval can be easily changed by writing the desired value to the corresponding EEPROM cell of the set-top box microcontroller. For joint operation of the set-top box with the meter-indicator [2], the codes from the file Ind_Stat_UNIVERSAL_SBM1.HEX, attached to the article, must be loaded into the memory of the DD20 microcontroller. To download them, I used a self-made programmer [5] running WinPic800 v3.60. Any other one that can work with the PIC12F683 microcontroller will do. The program occupies almost the entire FLASH memory of this microcontroller. Together with the radiation meter-indicator [2], the device determines and displays on the LCD the statistical indicators of the level of radioactive radiation in a sample of 50 measurements (maximum) in three modes: 1. Construction of a histogram of the results of the last fifty measurements with a duration of 34 s. It is the number of pulses counted for such a time in the device [2] of the Geiger-Muller counter SBM-20 that is equal to the radiation intensity in microroentgens per hour. The LCD screen of the statistical indicator in this mode looks as shown in Fig. 2. It also shows the areas for displaying various parameters on the screen.
2. Construction of a histogram of the last fifty values of the mean hourly radiation intensity (Fig. 3). Only one of every 106 pulses of the Geiger-Muller counter is taken into account in their calculation. That's how many 34-second intervals fit into one hour.
3. Construction of a histogram of the last fifty values of the average daily radiation intensity (Fig. 4). Each of them is calculated by the program as an average of 24 hourly measurements.
Regardless of the set mode, the device calculates and displays the following information on the LCD screen: - minimum, maximum and average values of the results of measurements completed and displayed on the screen. The program calculates the average value by summing the results of these measurements (moreover, values exceeding 99 units are ignored) and dividing the sum by their number, rounding the quotient to an integer; - histogram of measurement results. As their number grows, new elements of the histogram are added to the right. Upon reaching the maximum number of measurements (50), before adding each new result, the program shifts the entire histogram by one position to the left, while erasing the very first of the displayed results. The maximum value displayed on the bar graph is 40 µR/h. If it is exceeded, the program continues to accumulate the result up to 99 μR / h, but the image on the indicator becomes negative. Due to this, there is no need to constantly monitor the readings of the device in order to fix the excess of the threshold. To return to a positive display, press the button available in the statistical indicator; - the current level of charge of the battery built into the device. In modes 2 and 3, the program stores all the results of hourly and daily measurements displayed on the screen in the EEPROM of the microcontroller and, using this information, restores the image displayed on the screen before exiting one of these modes when returning to it. Analyzing the obtained histograms, one can notice that the average radiation level cannot be reliably determined from the result of a single measurement. The most informative was the histogram of hourly measurements. In the fig. In example 3, in the initial part of the histogram, a sharp rise in the radiation level was recorded when visiting the stone grottoes of the landscape park, although the norm was still not exceeded. Then there is a difference in levels inside the concrete and brick buildings - a kind of wave of about twelve hours duration. The reason for the increased level of radiation in the stone grotto is obvious, but the conclusion about the influence of the building material is speculative. The histogram of daily measurements shows a relatively stable level. If necessary, the backlight of the LCD screen can be turned on in the device. Without it, the current consumed by the device does not exceed 0,55 mA, which, with a battery capacity of 650 mAh, allows it to remain operational for about 49 days during round-the-clock operation. Shown in Fig. 5, the schematic diagram of the set-top box does not need special explanation, since its main functions are implemented in software. The XS1 (miniUSB) connector of the charging control board of the G1 lithium-ion battery built into the set-top box is supplied with a constant voltage of 5 V from any standard charger or from the USB connector of a computer.
The charging control board is ready-made [6], there are many of them on the market today. If desired, it can be made independently by using the TP4056 chip. The charging voltage from connector XS1 is also connected to connector XS2, so that when a statistical meter is connected to a meter-indicator, the battery of the latter is also charged. In order for the pulses from the meter-indicator to arrive at pin 3 of the XS2 connector of the statistical indicator, the meter-indicator, the circuit of which is shown in fig. 2 in [2] has undergone minimal modification. Pin 3 of its XS1 connector is connected through a 10 kΩ resistor to the collector of transistor VT1. In the statistical indicator, these pulses through the resistor R1 enter the GP2 pin of the DD1 microcontroller, which is assigned in the program as the input of interrupt requests generated by the falling drops of the incoming pulses. The microcontroller performs all further processing of information and the output of its results on the HGl LCD. The battery voltage G1 is supplied to the power supply circuit of the microcontroller DD1 and the indicator HG1 through the integral stabilizer DA1 (LP2980-3.0 [7]) at 3 V. An important feature of this stabilizer is its own low current consumption, not exceeding 170 μA at a load current of 1 mA. The designations and numbers of LCD pins on the diagram correspond to the markings printed on its board near the contact pads for external connections. There are two rows of them - under the indicator screen and above it. Both rows are equal, each consists of eight pads that simply duplicate the pads of the other row. This is done for the convenience of connecting the LCD to the device that controls it. The purpose of the LCD pads is as follows: 1. RST - signal input for setting the PCD8544 [8] controller built into the indicator to its initial state (low level - installation, high level - operation). 2. CE - signal input to enable information input into the indicator controller (low level - allowed, high level - not allowed). 3. DC - input of the destination signal of the code loaded into the controller (low level - command, high level - information for display). 4. DIN - information input of the serial interface. 5. CLK - serial interface clock input. 6. VCC - LCD supply voltage plus (2,7...3,3 V). On the Internet, you can find reports that the supply voltage can reach 5 V. But I did not check this. 7. Light - screen backlight power supply. There are two modifications of the Nokia 5110 LCD on blue and red printed circuit boards. To turn on the backlight, a positive polarity voltage must be applied to the Light contact pad if the board is blue, or connected to a common wire if the board is red. In both cases, it is desirable to install a current-limiting resistor in series with the Light circuit, although the red board already has such 300 Ohm resistors for each of the four backlight LEDs. With an additional 100 ohm resistor (R3), the backlight on the red board draws about 3mA of current. 8. GND - common wire. After supplying voltage to LCD Nokia 5110 for its normal operation, the program of the microcontroller DD1 must perform the initialization procedure. It starts with a signal to set the built-in LCD controller to the initial state, after which it writes to the controller all the parameters necessary for the operation of the LCD, including the order of automatic change of addresses along the X and Y axes, a sign of a positive or negative image on the screen, etc. Procedure in detail initialization is described in [8]. Commands or information are transmitted to the LCD byte by byte in serial code, starting with the most significant bit of each byte. Each digit of the code supplied to the DIN input is read by the LCD controller using the rising edge of the next pulse at the CLK input. LCD Nokia 5110 displays 48x84 = 4032 dot elements on its screen. In fact, the display field consists of six lines with a height of eight dots and a length of 84 dots. In the device under consideration, the LCD is installed rotated by 180о around a perpendicular to the center of the screen relative to the standard position. Therefore, a byte with zero addresses on the horizontal (X) and vertical (Y) axes of the screen will be displayed in its lower right corner. The author considers this option the most convenient for displaying histogram columns, since in this case, when the column height increases and its end moves to the next byte, the address of this byte along the Y axis also increases. With the origin at the top left of the screen, increasing the height of the histogram bar would require decreasing the y-address. As a result of the rotation of the LCD, two features of displaying information on its screen arise. First, each information byte is displayed on the screen from top to bottom, starting with the most significant digit and ending with the least significant one. Secondly, due to the fact that during initialization the mode of automatic increase in the address along the X axis is set, the characters (represented, as a rule, by sets of six bytes) are displayed on the screen in the direction from right to left. This is how you need to set the output inscriptions in the program. The format of each character in six-byte encoding is 5x7 dots. The sixth byte of the code and the least significant digits of the previous five bytes, which have zero values, create gaps on the screen between characters and their strings. The Nokia 5110 LCD allows displaying the contents of 504 bytes of information on the screen, but does not allow the instrument's microcontroller to read the current screen contents. Therefore, the task of storing part of its contents necessary for further use is assigned to the microcontroller, the EEPROM size of which is only 256 bytes. After the information byte is displayed on the screen, its image remains unchanged until the supply voltage is turned off or until another byte is written to the same address. In this regard, I had to programmatically clear the screen. Otherwise, if you try to display a histogram column with a height of, say, seven points in place of where a 16-point column was previously, a 16-point column will remain on the screen, only with the eighth point canceled. The prefix is assembled by surface mounting on a breadboard. The DD1 microcontroller is installed in a standard panel, which ensures its easy reprogramming if necessary. The board is placed in a case with external dimensions 74x53x17 mm from a Mini DV standard video cassette. For the power switch SA1, the control button SB1, the backlight button SB2 and for connecting cables to the XS1 and XS2 connectors, holes are cut in the case. Consider the features of the DD1 microcontroller program, which are important primarily for those who want to change it. The assembly language program was created and translated using the MPLAB IDE v8.30 development and debugging environment. To reduce the amount of program text and make it more readable, a set of macro commands is used, the definitions of which are collected in the KOROT-KO.inc file. This file must be located in the same folder as the source code of the program (*.asm file), otherwise the macro commands will not be accepted by the assembler. It should also be taken into account that when using instructions like BTFSS, which, under certain conditions, provides for skipping the instruction following it, not the entire macro instruction will be skipped, but only the first instruction from it. In such situations, you have to use the GOTO instruction as a skipped instruction and insert the macro only at the jump address. As mentioned above, the size of the microcontroller's EEPROM does not allow storing all the information displayed on the screen, especially for three modes. In addition, if the results were written every 34 s, the EEPROM resource of 1000000 write cycles would be exhausted in about a year of operation. Therefore, the program writes to EEPROM only at the end of each hour of operation, and only in modes 2 and 3. In mode 1, no recording is performed, so when switching to this mode, the histogram construction starts again. The logic of the program is as follows: - 50 REZULT1-REZULT50 registers are allocated in the register memory of the microcontroller to store the results of completed measurements, which the program then displays on the LCD screen. To ensure hourly or daily recording in EEPROM, the program has a counter of minutes, hours and days of work; - when switching to mode 2 or 3, the information stored in the EEPROM, the program rewrites to the REZULT1-REZULT50 registers (or to some of them, if the number of performed measurements has not reached 50), and then displays it on the screen. In other words, the contents of the same registers are always displayed on the LCD screen, but when the mode is changed, the program transfers information corresponding to the new mode from EEPROM to them. Further changes in the information in the registers occur in accordance with the selected operating mode of the device. Direct access to such a large number of registers would be too cumbersome, so indirect addressing is used. Its essence is that the address of the register with which to work, for example REZULT1, is entered by the program into the FSR register, after which all operations performed on the contents of the physically non-existent INDF register are actually performed on the contents of the REZULT1 register. When the content of the FSR register is increased by one, the same thing will happen with the REZULT2 register, etc. Naturally, all processed registers must be located in memory without gaps and in the order in which their contents must be processed. By analogy with the system register of the microcontroller STATUS, the program created registers KONTR_REG and KONTR_IND_REG, the value of each digit of which corresponds to the fulfillment of certain conditions (for example, the achievement of the maximum number of measurements displayed on the histogram or the need to display a dashed line). This allows not to check the fulfillment of these conditions each time, but only to monitor the state of the corresponding bits of the registers. When loading codes from a HEX file into the microcontroller, a set of bytes will be written to the first 84 EEPROM cells (from address 0x00 to 0x53), which form the upper string of characters on the LCD screen, which does not change when the program is executed. The rest of the EEPROM content is generated by the program during execution: - contents of six service registers and 50 measurement results in mode 2; - contents of six service registers and 50 measurement results in mode 3; - at address 0xFB, the number of days spent by the battery. Initial value - 0; - at address 0xFC, the number of hours that the battery has left to work in the current day. Initial value - 24 (0x18); - at address 0xFD the planned number of days of battery operation; - at address 0xFE number of measurements per hour; - at address 0xFF, the duration of one measurement in seconds. The contents of the last three cells, if necessary, can be changed using the programmer. The table of codes for all numbers and letters of modes displayed by the program on the indicator is located at the end of the program (FLASH) memory of the microcontroller, starting from address 0x760. It is taken into account that the characters are displayed on the screen from right to left. The PIC12F683-I/P microcontroller has 96 general-purpose registers in the zero bank and 32 such registers in the first bank. It was not possible to use only the zero bank in the program, since only 50 registers were allocated for the measurement results. Working with the registers of the first bank also led to the need to repeatedly change the number of the used bank in the process of program execution. This must be taken into account when modifying the program. The main loop of the program is empty. The program performs all its tasks in the following interrupt handling procedures: - by falling level difference at the GP2 input (processing of a pulse from a Geiger-Muller counter); - by changing the level at the GP3 input (processing pressing the SB1 button). In addition to switching the modes of operation of the statistical indicator, this button allows you to reset the counter of the time worked out by the battery after charging. To do this, turn on the device while pressing the button. If, after such switching on, the button is kept pressed for more than 3 s, the measurement results will additionally be completely reset to zero; - by timer 1 overflow. At a frequency of the internal microcontroller generator of 2 MHz, the overflow period is 1 s (taking into account software adjustment). Based on the described add-on, a second device was developed - an autonomous statistical radiation meter, shown in the photograph in Fig. 1 right. For this, a block was added to the considered indicator-attachment, the scheme of which is shown in Fig. 6 (the numbering of elements continues that started in Fig. 5), developed on the basis of the indicator meter [2]. The wires marked in fig. 6 letters A, B and C, should be connected with the same points in the diagram of fig. 5, and remove the XS2 connector.
In contrast to [2], a miniature Geiger-Muller counter SBM-21 (BD1) was used, the dimensions of which (length - 21 mm, diameter - 6 mm) made it possible to fit a fully functional device in the same case from a Mini DV video cassette as the considered one. attachment above. The appearance of a stand-alone device in a case, but without an overlay with explanatory inscriptions on the front panel, is shown in fig. 7.
Note. On the LCD screen in Fig. 7 inscriptions in Ukrainian are displayed: year (year) - hour, wimir. (vimipiv) - measurements. The SBM-21 counter, voltage multiplier (VD1-VD7 diodes, capacitors C4, C6-C9, C11, C12) and an additional microcontroller DD2 are located at the top of the board. To do this, I had to cut the LCD board by removing its lower (upper in Fig. 7) row of contact pads. Vibration motor M1 with transistor VT2 and voltage regulator DA1 are located under the battery charging control board in the lower right part of the main board. Hanging installation. Panels are provided for microcontrollers. The operation and configuration of the Geiger-Muller counter unit is similar to that described in detail in [2], so we will only consider the changes made to the circuit and program. Instead of a high-voltage bipolar transistor, an insulated gate field effect transistor BS1A (VT107) was used as an electronic key in the high voltage driver for the BD3 counter, which reduced the current consumed by this node by about three times. The LED indicators of battery voltage and radiation level are excluded, since these functions are assigned to the HG1 LCD, which is already present in the indicator-attachment. A transistor was used in the unit for setting the microcontroller to its initial state in the device [2]. As a result of the changes made to the program, this node is no longer needed, and the released transistor (VT2) is used to control the vibration motor M1 from a cell phone. Signaling the supply voltage, the DD2 microcontroller turns on this motor for a short time, and when working intermittently, the vibration motor signals the radiation level exceeding 99 μR / h. The microcontroller turns on the sound (piezo emitter HA1) and light (HL1 LED) pulse repeaters of the BD1 counter when the radiation level is more than 40 μR / h or when the SB3 button is pressed. The operating voltage of the SBM-21 counter is 260...320 V [3], which is less than that of the SBM-20. The pulses generated by the microcontroller DD2 at the gate of the transistor VT3 provide a voltage on the counter of 300 V. The device with the SBM-20 counter performs 50 measurements in about 28 minutes. But with the SBM-21 counter, this interval is much longer - 4 hours 10 minutes. For the convenience of analyzing instrument readings, in addition to short dashed lines marking every tenth measurement in the upper part of the screen, and vertical dashed lines marking every 24 hours, dashed lines marking hourly intervals have been added in the hourly measurement mode. The countdown on the screen goes from right to left. This makes it easier to determine what the radiation level was an hour or a day ago. To reduce the current consumption, the clock frequency of microcontrollers DD1 and DD2 is reduced to 250 kHz. The repetition period of timer 1 overflows in both microcontrollers has been increased to 6 s. This entailed a rather slow drawing of the image on the screen when turning on and changing the mode, but it made it possible to bring the total current consumed by the device to 0,66 mA. With a 650 mAh battery, a stand-alone device can work for more than 40 days. To work with the SBM-21 counter block, you need to load the program from the Ind_Stat_SBM1.HEX file into the DD21 microcontroller. When a program is loaded into the DD2 microcontroller from the HV_SBM21.HEX file, the values of the parameters necessary for its operation are automatically entered into the EEPROM of the microcontroller: - address 0x00 contains the duration of one measurement in six-second timer 1 overflow periods (0x32); - at address 0x01 there is an experimentally selected value 0x61 of the parameter that sets the supply voltage of the SBM-21 counter. The larger this value, the lower the voltage; - address 0x02 contains the value of the first threshold (0x28 - 40 μR/h); - address 0x03 contains the value of the second threshold (0x63 - 99 µR/h). If necessary, these values can be easily changed by correcting the contents of the corresponding EEPROM cells. In conclusion, I would like to emphasize that the performance of both devices described in this article was tested for almost two months. Nevertheless, their software does not claim to be optimal, since it was developed by the method of progressive complication. The author carried out some improvements to the programs already in the process of writing the article. It is noteworthy that the expansion of the functionality of the devices did not require changes in their circuits and design. Microcontroller programs can be found at ftp://ftp.radio.ru/pub/2017/03/stat-izm.zip. Literature
Author: S. Makaretz
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