The Kynix Components

As we all know, switching regulated power supplies are widely used in electronic equipment due to their small size, lightweight, and high conversion efficiency. However, this type of power supply is only suitable for occasions where the output voltage is fixed or the range of change is small. Therefore, this paper proposes a series switching power supply composed of a monolithic switching regulator LM2576  -ADJ instead of a linear regulator. In addition to the advantages of a wide range of linear power supplies, the power supply efficiency is greatly improved. The maximum output power of this circuit is about 75w, the voltage adjustment range is 1.23V~25V, and the output current can reach 3A.Catalog I. Circuit ConfigurationII. Principle Analysis2.1 Voltage Stabilizing Circuit2.2 Voltage Adjustment Circuit2.3 Voltage Display CircuitIII. Overall CircuitIV. ConclusionFAQOrdering & Quantity I.Circuit ConfigurationThe whole circuit is composed of four parts: a step-down rectifier circuit, a voltage stabilizing circuit, a numerical control circuit, and a digital display circuit. Its circuit block diagram is shown in Figure 1.Figure 1. System block diagramII.Principle Analysis 2.1 Voltage Stabilizing Circuit The voltage stabilizing part of this circuit uses LM2576. In order to generate different output voltages, the negative terminal of the comparator is usually connected to a reference voltage  (1.23V), and the positive terminal is connected to a voltage divider resistor network. The output voltage through the voltage divider resistor network is compared with the internal reference voltage of 1.23V. If there is a deviation in the voltage, an amplifier can be used to control the output duty cycle of the internal oscillator to keep the output voltage stable. Its typical application circuit is shown in Figure 2.Figure 2. Typical application circuit with adjustable output voltageIn the figure, +V1N is the voltage input terminal. The 4 pins of the regulator control terminal are connected to the voltage divider circuit composed of potentiometer W and resistor R. Changing W can change the voltage division ratio and adjust the output voltage. The relationship between the output voltage Vout and R1 and R2 is Uo=UREF(1+R2/R1), and the reference voltage  UREF of the voltage regulator sampling circuit is 1.23V.The choice of inductance L1 should be based on the LM2576 output voltage, maximum input voltage, maximum load current, and other parameters. First, calculate the voltage·microsecond constant (E·T) according to the following formula:In the above formula, Vin is the maximum input voltage of LM2576.  Vout is the output voltage of LM2576, and f is the operating oscillation frequency value of LM2576  (52KHz). After E·T is determined, you can refer to the corresponding voltage·microsecond constant and load current graph to find the required inductance value, as shown in Figure 3.Figure 3. Curves of voltage·microsecond constant and load currentIn this circuit, Vin=28V, Vout=25V, so according to the formula:It can be seen from the figure that according to the maximum load current selection, the value of the inductance L should be 68μH. CIN is the input filter capacitor, which should generally be greater than or equal to 100μF. It is required to be as close as possible to the input pin of LM2576 during installation, and its withstand voltage value should match the maximum input voltage value. COUT is the filter capacitor at the output end, and the capacitor should be valued according to the following formula:Where Vin is the maximum input voltage of LM2576, Vout is the output voltage of LM2576, and L is the value of inductance L1 selected by calculation and lookup table. The withstand voltage value of capacitor C should be greater than 1.5 to 2 times the rated output voltage. Diode D1 selects the Schottky diode of the MBR360 series. 2.2 Voltage Adjustment Circuit The voltage adjustment part of this circuit uses the electronic potentiometer X9511 as the voltage adjustment unit. Its typical application diagram is shown in Figure 4. X9511 contains 31 series resistance arrays and 32 shaft heads. The position of the shaft head is controlled by two buttons and can be stored in the internal EEPROM memory for recalling when the power is turned on next time, and the shaft head position is automatically restored. Voltage adjustment circuit diagram, see Figure 5.Figure 4. Typical application diagram of X9511Figure 5. Voltage adjustment circuitAccording to the application principle of LM2576-ADJ, its output voltage Uo=(1+R/R2), where R can choose a digitally controlled potentiometer composed of IC3 (X9511, 50K), UREF=1.23V, Uo=UOMAX=25V, and so:That is, the value of R2 is about 2.6KΩ. From the above analysis, we can see that the voltage adjustment range of this circuit is approximate as follows:When R is 0Ω：When R is 50KΩ: 2.3 Voltage Display Circuit In this unit, we use a voltage display circuit composed of MAX1496. Its working power supply is a single power supply from 2.7V to 5.25V. The typical application circuit is shown in Figure 6, and the voltage display circuit is shown in Figure 7.Figure 6. M-AXI496 typical application circuitFigure 7. Using the resistance divider method to extend the rangeThe RANGE pin is a rate selection pin. Since the displayed voltage range is 1.23V~25V, and its range is up to 2V, if you want to display the voltage correctly, you should expand its range to 200V. To expand the range, you can use the resistor divider method. Add a voltage divider circuit as shown in figure 7 between AIN+ and AIN1 of the MAX1496. According to the resistance value in the figure, it can be calculated that the range has been expanded by 100 times， that is 200V. At this time, the maximum voltage of 200V is measured, and after the voltage is divided by the voltage divider circuit, the full-scale voltage of 200V×0.01=2V can be obtained.DPSET1 and 2 pins set the display position of the decimal point for display in different ranges. The specific settings and effects are shown in Table 1. Because the full-scale display in this circuit is 200V, the first setting format in the table can be selected, and its display resolution is 0.1.DPSET1DPSET2DISPLAY OUTPUTZEROINPUT READING00188.80.00118.880.001018880111.8880.000X＝Don’t care.Table 1. MAX1496 decimal point display settingsThe HOLD and PEAK pins are the setting bits for data retention and peak display, and their specific settings and effects are shown in Table 2. The first is the latched state, which is used to save the measured value; the second is the peak display mode, which is used to display the highest value measured. In this example, you can choose the last way to display the latest results.HOLDPEAKDISPLAY VALUES FORM1XHold value01Peak value00Latest ADC resultX＝Don’t care.Table 2. MAX1496 display mode settingMAX1496 adopts the dynamic display mode of bit segment scanning, its display scanning frequency reaches 640Hz, the display is stable and clear, and the power consumption is greatly reduced compared with a static display. In this design, the commonly used four-digit scanning LED display can be used. III.Overall Circuit The overall circuit is shown in Figure 8. After the commercial power is stepped down by the transformer T, the bridge rectifier circuit  D1 and the filter circuit formed by the capacitor C1 convert the low-voltage AC into a DC voltage of about 30V. One of this voltage is sent to the voltage of IC2 (LM2576). At the input end, the other way sends a +5V power circuit composed of VT1, D2, and IC1 (LM7805) as the working power supply for IC3 (X9511) and JC4 (MAX1496).Figure 8. System diagramIV. ConclusionThis article summarizes the design scheme of a digitally controlled adjustable switching power supply based on LM2576.  which has the advantages of simple circuit, reliable, high conversion efficiency, and low price. Only a few components in the circuit can form a switching regulator with a supply current of 3A. When the circuit is used for lighter loads, LM2576 does not need to install a radiator, which not only saves equipment space but also reduces heat loss. After actual testing, its performance indicators can fully meet general needs, it is the best substitute for the popular three-terminal linear regulator.FAQWhere is LM2576 used?LM2576 is usually used as a voltage stabilizing device when the input and output voltage difference is large and the output current is also large. Because it is a switching regulator, it has a higher conversion efficiency and low heat generation than a linear regulator.What’s the difference between LM2576T-ADJ and LM2576S-ADJ?LM2576T-ADJ is the package of TO-220, LM2576S-ADJ is the package of TO-263-5, there is no difference in their functions.What is the difference between LM2940 and LM2576? Which circuit are they applicable to?LM2940 is a low-dropout linear stabilized integrated circuit. The linear stabilized power supply is characterized by a relatively simple circuit, high precision, and small ripple coefficient. It is suitable for precision power supplies with high voltage requirements. The disadvantage is that the efficiency is very low and the output The current is relatively small (relative to the switching power supply)LM2576 is a switching power supply integrated circuit. Switching power supply, the circuit is more complicated, but the output current is large, the efficiency is high, the disadvantage is that the accuracy is lower and the ripple coefficient is larger.Why do switching power supply chips LM2576 and LM2596 have diodes, inductors and capacitors behind the output pins?The function of the diode and the inductance is that the output current can be continuous when the LM25XX is in the off state, and the function of the capacitor is to prevent the output voltage from sudden changes when the LM25XX is turned on and off. In fact, it is filtering.Why the higher the switching frequency of LM2576 and LM2596, the smaller the output inductance and capacitance value?Quite simply, the capacitive reactance of a capacitor decreases as the frequency increases, and the inductance of an inductor increases as the frequency increases. That is to say, the effect of using an inductance of 33uH in the case of 150Khz is basically the same as the effect of using an inductance of 100uH in the case of 52khz, and the principle of capacitance is the same. LM2596 is an upgraded version of LM2576. But LM2576 also has the advantage of less switching loss and less interference.

I DescriptionFirst, this blog will introduce the 1 wire digital temperature sensor DS18B20. We mainly introduce its structure, characteristics, and working principle here. Second, we will introduce a temperature measurement system based on DS18B20 and AT89S52 microcontrollers. Here we mainly introduce its hardware structure and assembler. Third, there will be part of the source program that is detailed analyzed. Finally, the blog also explains how it performs temperature measurement in the agricultural field.The temperature measuring device has a series of advantages. Such as high display accuracy, low price, simple structure, convenient expansion, and wide application.DS18B20 Temperature Sensor TutorialCatalogI DescriptionII IntroductionIII DS18B20 Overview3.1 DS18B20 Advantages3.2 DS18B20 Features3.3 DS18B20 Internal StructureIV  DS18B20 MCU Temperature Measurement Device4.1 Composition of System Hardware4.2 Design of InterfaceV Software DesignVI Application in Agricultural Production6.1 Temperature of Mildew6.2 Temperature of Agricultural Products6.3 Temperature Detection in Greenhouses6.4 Temperature of SoilVII ConclusionFAQOrdering & QuantityII IntroductionWhat is temperature?What are the roles of temperature?Temperature is a physical quantity that characterizes the degree of cooling of an object, and it is also a basic environmental parameter. In agro-industrial production and daily life, the measurement and control of temperature always occupy an extremely important position.At present, a typical temperature measurement and control system consists of the following parts:Analog temperature sensor;A/D conversion circuit;MCU.However, the analog signal output by the analog temperature sensor has to be converted. It can interface with microprocessors such as single-chip microcomputers only after obtaining digital signals through the A/D conversion link. Therefore, the hardware circuit structure is complicated and the cost is high.But DS18B20 can help solve this problem. The new 1 wire digital temperature sensor represented by DS18B20 integrates temperature measurement and A/D conversion and directly outputs digital quantities. The structure of the interface circuit with the single-chip microcomputer is simple, and it is widely used on occasions with long-distance and many nodes. Therefore, DS18B20 has strong promotion and application value.III DS18B20 Overview3.1 DS18B20 AdvantagesDS18B20 type 1 wire intelligent temperature sensor produced by DALLAS Semiconductor Company. It belongs to a new generation of intelligent temperature sensors adapted to microprocessors. Compared with the traditional thermistor, it has the following advantages:It can directly read the measured temperature;The reading mode of 9-12 digits can be realized through simple programming according to actual requirements;It can also complete 9-bit and 12-bit digital quantities within 93.75ms and 750ms, respectively, with a maximum resolution of 0.0625°C;To read or write the information of DS18B20, only one port line (1 wire interface) is required to read and write.3.2 DS18B20 FeaturesUnique 1-Wire® Interface Requires Only One Port Pin for Communication Reduce Component Count with Integrated Temperature Sensor and EEPROM Measures Temperatures from -55°C to +125°C (-67°F to +257°F)±0.5°C Accuracy from -10°C to +85°C Programmable Resolution from 9 Bits to 12 BitsNo External Components RequiredParasitic Power Mode Requires Only 2 Pins for Operation (DQ and GND )Simplifies Distributed Temperature-Sensing Applications with Multidrop Capability Each Device Has a Unique 64-Bit Serial Code Stored in On-Board ROMFlexible User-Definable Nonvolatile (NV) Alarm Settings with Alarm Search Command Identifies Devices with Temperatures Outside Programmed LimitsAvailable in 8-Pin SO (150 mils), 8-Pin µSOP, and 3-Pin TO-92 Packages3.3 DS18B20 Internal StructureDS18B20 adopts 3-pin PR-35 package or 8-pin SOIC package.Its DS18B20 external shape and pin diagram are shown in Figure 1.The DS18B20 internal structure block diagram is shown as in Figure 2.The structure of 64-bit flash ROM is shown in Figure 3.Figure 1. DS18B20 PinoutFigure 2. DS18B20 Internal StructureFigure 3. 64b Flash ROM StructureIV  DS18B20 MCU Temperature Measurement Device4.1 Composition of System HardwareThe DS18B20 single-chip microcomputer intelligent temperature measurement device is mainly composed of the DS18B20 temperature sensor, AT89S52, display module, and power module, as shown in Figure 4.The main technical indicators of the product are:Measuring Range (℃): -55.0~+125.0Measurement Accuracy (℃): 0.1Response Time (s): ≤1.5　　Figure 4. System Structure DiagramThe system uses DS18B20 as a temperature sensor. The one-chip computer AT89S52 of  ATMEL Company serves as the processor. Temperature display and light-emitting diode as temperature control output unit. The whole system strives to have a simple structure and perfect functions.The working principle of the system is as follows: After DS18B20 carries on the field temperature measurement, the measured data is sent to the P3.5 port of AT89S52. The temperature value is displayed after being processed by the microcontroller. Then, this temperature value is compared with the upper limit of the set alarm temperature. If it is higher than the set upper limit, the yellow LED lights up.The main circuit diagram of the system is shown as in Fig. 5.Figure 5. DS18B20 Temperatuer Measurement Device4.2 Design of InterfaceThere are 2 ways to connect DS18B20 to the hardware of the microcontroller:Vcc is connected to external power supply, GND is grounded, and I/O  is connected to the I/O  line of the microcontroller;Use the parasitic power supply, UDD and GND are grounded at this time, and I/O  is connected to MCU  I/O,  Regardless of the 1st or 2nd power supply mode, the I/O  line must be connected to a pull-up resistor of about 4.7kΩ. Figure 6 shows a typical connection between DS18B20 and a microprocessor.In Figure 6(a), DS18B20 adopts parasitic power supply, and its VDD and GNG terminals are both grounded;In Figure 6(b), the DS18B20 uses an external power supply, and its VDD terminal uses a 3~5.5V power supply.This system adopts the wiring mode shown in Figure 6(b), that is, the working mode of external power supply. The actual connection picture of the system is shown in Figure 6.Figure 6. Physical Diagram of System ConnectionV Software DesignIt is worth noting that DS18B20 has very high requirements on two aspects: timing and electrical parameters. Therefore, the work flow of the main CPU accessing the DS18B20 through the single-bus interface must follow a strict operating sequence: first, initialize the DS18B20; second, send ROM commands; and then, send function commands.We can take a look at the following part of the source program is as follows:ORG 0000HAJMP MAIN; Statement of MCU memory allocation!TEMPER_L EQU 29H; used to save the lower 8 bits of the read temperatureTEMPER_H EQU 28H; used to save the upper 8 bits of the read temperatureFLAG1 EQU 38H; Whether the DS18B20 flag is detectedPNFLAG EQU 68H; Data positive and negative flagA_BIT EQU 20H; the single digit of the digital tube stores the memory locationB_BIT EQU 21H; The ten digits of the digital tube store the memory locationC_BIT EQU 22H; The decimal places of the digital tube store the memory locationT_INTEGER EQU 26H; The integer part after FORMAT, which integrates two bytes of temperature into one byteT_DF EQU 27H; The decimal fraction after FORMAT, the decimal fraction of nibble temperature (there are low four digits)MAIN:LCALL GET_TEMPER; Call the temperature reading subroutineLCALL T_FORMAT; Format the read 2 byte temperatureLCALL ALARM; call the alarm subroutineLCALL DISPLAY; call the digital tube display subroutineLCALL D1S; test after a delay of 0.5 secondsAJMP MAIN; this is the DS18B20 reset initialization subroutineINIT_1820: SETB P3.5NOPCLR P3.5; the host sends out a reset low pulse with a delay of 537 microsecondsMOV R1,#2TSR1: MOV R0,#250DJNZ R0,$DJNZ R1, TSR1SETB P3.5; then pull up the data lineNOPNOPNOPMOV R0,#25HTSR2: JNB P3.5, TSR3; waiting for DS18B20 responseDJNZ R0, TSR2; delayLJMP TSR4TSR3: SETB FLAG1; Set the flag bit to indicate that DS1820 existsLJMP TSR5TSR4: CLR FLAG1; clear the flag bit, indicating that DS1820 does not existLJMP TSR7TSR5: MOV R0,#120TSR6: DJNZ R0, TSR6; timing requires a period of delayTSR7: SETB P3.5RET; read the temperature value after conversionGET_TEMPER: ;SETB P3.5LCALL INIT_1820; first reset DS18B20JB FLAG1, TSS2RET; Determine whether DS1820 exists? If DS18B20 does not existThen returnTSS2: MOV A,#0CCH; skip ROM matchingLCALL WRITE_1820MOV A, #44H; Issue temperature conversion commandLCALL WRITE_1820LCALL DISPLAYLCALL INIT_1820; reset before reading temperatureMOV A, #0CCH; Skip ROM matchingLCALL WRITE_1820MOV A, #0BEH; Issue read temperature commandLCALL WRITE_1820LCALL READ_18200; save the read temperature data to 28H/29HRET; Write DS18B20 subroutine (with specific timing requirements)WRITE_1820: MOV R2,#8; a total of 8 bits of data;CLR CWR1: CLR P3.5MOV R3,#6DJNZ R3,$RRC AMOV P3.5,CMOV R3,#23DJNZ R3,$SETB P3.5NOPDJNZ R2,WR1SETB P3.5RET; read the program of DS18B20, read two bytes of temperature data from DS18B20READ_18200: MOV 36H, #2; Set the high and low temperatureRead from DS18B20MOV R1, #29H; the low bit is stored in 29H (TEMPER_L), the high bitDeposit 28H (TEMPER_H)RE00: MOV R2,#8; There are 8 bits of dataRE01: ;CLR CSETB P3.5NOPNOPCLR P3.5NOPNOPNOPSETB P3.5MOV R3,#9RE10: DJNZ R3, RE10MOV C,P3.5MOV R3,#23RE20: DJNZ R3, RE20RRC ADJNZ R2,RE01MOV @R1,ADEC R1DJNZ 36H,RE00RET;-----Integrate the two-byte temperature read out (please refer to the information about the 2-byte temperature format read out by DS18B20) ----------T_FORMAT:;Alarm subroutineALARM:; Display subroutineDISPLAY:; 1MS delay (calculated by 12MHZ)D1MS: MOV R7,#250llmm:nopnopDJNZ R7,llmmRET; 1MS delay (calculated by 12MHZ)D1S: Mov R6,#4LOOP2: mov R5,#125; ------------ 250LOOP1: LCALL D1mSDJNZ R5,LOOP1DJNZ R6,LOOP2RET; 7-segment digital tube 0-9 digit common anode display codeNUMTAB: DB0C0H,0f9H,0a4H,0b0H,99H,92H,82H,0f8H,80H,90H,0ffHXIAOSHU:DB00H,01H,01H,02H,03H,03H,04H,04H,05H,06H,06H,07H, 08H, 08H, 09H, 09HENDVI Application in Agricultural ProductionThis temperature measurement system can directly output digital quantities. In addition, it has the characteristics of simple structure, convenient use and low price. Therefore, it can be widely used in agricultural production.6.1 Temperature of MildewModern grain warehouses can use this system to monitor the temperature of hundreds of points. In this way, you can easily grasp the temperature changes at various points at different times, increase storage capacity, and effectively reduce the occurrence of mildew.6.2 Temperature of Agricultural ProductsAt present, low-temperature refrigeration measures are widely adopted for the preservation of fruits and vegetables. The system can be installed in the temperature measurement position of the refrigerator compartment. In this way, the temperature value can be conveniently observed at any time to check whether the optimal preservation temperature is reached.6.3 Temperature Detection in GreenhousesThe system is used in plastic greenhouses for greenhouse vegetable cultivation and flower production. In this way, automatic temperature display can be realized, and labor and time for temperature measurement can be saved.6.4 Temperature of SoilIn the process of planting crops with strict requirements on soil temperature, the system can test the changes in soil temperature as needed to facilitate the grasp of accurate temperature values.VII ConclusionThe single-chip temperature measurement system takes full advantage of the simplicity of the hardware structure of DS18B20 and AT89S52, using 8-segment digital tube display, low price and wide application. According to actual needs, we can also use LCD as a display device or form a distributed temperature measurement and control system.Although the design is easy to expand, it also has its shortcomings. The simplicity of the hardware structure comes at the expense of software. Therefore, special attention should be paid to the working sequence requirements of DS18B20 during programming.In short, the system can be widely used in temperature measurement in agricultural production.FAQWhat is DS18B20 temperature sensor?The DS18B20 is a 1-wire programmable temperature sensor from maxim integrated. It is widely used to measure temperature in hard environments like in chemical solutions, mines or soil etc. The constriction of the sensor is rugged and also can be purchased with a waterproof option making the mounting process easy.How does the DS18B20 work?It works on the principle of direct conversion of temperature into a digital value. Is DS18B20 a thermistor?A thermistor is a thermal resistor - a resistor that changes its resistance with temperature. Thermistors have some benefits over other kinds of temperature sensors such as analog output chips (LM35/TMP36 ) or digital temperature sensor chips (DS18B20) or thermocouples.How accurate is DS18B20?The DS18B20 reads with an accuracy of ±0.5°C from -10°C to +85°C and ±2°C accuracy from -55°C to +125°C.What is ds1820?The DS18B20 is one type of temperature sensor and it supplies 9-bit to 12-bit readings of temperature. The communication of this sensor can be done through a one-wire bus protocol which uses one data line to communicate with an inner microprocessor.How do I connect my DS18B20 to my Raspberry Pi?Once you've connected the DS18B20, power up your Pi and log in, then follow these steps to enable the One-Wire interface:1.At the command prompt, enter sudo nano /boot/config.txt , then add this to the bottom of the file:2.dtoverlay=w1-gpio.3.Exit Nano, and reboot the Pi with sudo reboot.What is the working principle of DS18B20?The DS18B20 Digital Thermometer provides 9 to 12-bit (configurable) temperature readings which indicate the temperature of the device. It communicates over a 1-Wire bus that by definition requires only one data line (and ground) for communication with a central microprocessor. In addition it can derive power directly from the data line (“parasite power”), eliminating the need for an external power supply.The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively. The default resolution at power-up is 12-bit.Where to use DS18B20 Sensor?The DS18B20 is a 1-wire programmable Temperature sensor from maxim integrated. It is widely used to measure temperature in hard environments like in chemical solutions, mines or soil etc. The constriction of the sensor is rugged and also can be purchased with a waterproof option making the mounting process easy. It can measure a wide range of temperature from -55°C to +125° with a decent accuracy of ±5°C. Each sensor has a unique address and requires only one pin of the MCU to transfer data so it a very good choice for measuring temperature at multiple points without compromising much of your digital pins on the microcontroller.How connect DS18B20 to Arduino?First plug the sensor on the breadboard the connect its pins to the Arduino using the jumpers in the following order: pin 1 to GND; pin 2 to any digital pin (pin 2 in our case); pin 3 to +5V or +3.3V, at the end put the pull-up resistor.On an ATMega328P, why is a DS18B20 temperature sensor returning incorrect temperature values?Several possibilities:1. If it is just reading a little high, it might be caused by “self heating”. Add a heat sink and/or make measurements less frequently.2. Especially if the values are really whacky, it might be code with errors or mis-wiring. Use a published sketch to check operation.3. The DS18B20 might be defective. Try another.4. It’s accurate to 0.5ºC.

The differential amplifier circuit is also called the differential circuit.It can not only effectively amplify the AC signal, but also effectively reduce the zero drift caused by the power supply fluctuation and the temperature change of the transistor, so it has been widely used. Especially, it is widely used in integrated operational amplifier circuits, and it is often used as the pre-stage of multi-stage amplifiers.Starting from actual production design, this blog discusses the shortcomings of discrete resistors, filtering, AC common mode rejection, and high noise gain.What a Differential Amplifier is along with the Derivation of the Equation Relating Input to OutputCatalogI Classic Four-resistor Differential AmplifierII CMRRIII Low Tolerance ResistanceIV Another Low-end Detection ApplicationV High Noise GainVI Single Capacitor Roll-offVII Capacitance between Input Terminals of Op AmpVIII ConclusionI Classic Four-resistor Differential AmplifierFigure 1 shows the classic four-resistor differential amplifier is very useful.Figure 1. Classical differential amplifierThe transfer function of this amplifier is:If R1 = R3 and R2 = R4, then Equation 1 is simplified to:This simplified theory works, but it cannot be done in reality. Because the resistance can never be exactly equal. In addition, other changes in the basic circuit can produce unexpected behavior. Although the following example is simplified to show the essence of the problem, it is derived from actual application problems.II CMRRAn important function of the differential amplifier is to suppress the common mode signal of the two inputs. As shown in Figure 1, assuming that V2 is 5 V and V1 is 3 V, then 4V is the common-mode input. V2 is 1 V higher than the common mode voltage, and V1 is 1 V lower. The difference between the two is 2 V, so the "ideal" gain of R2/R1 is applied to 2 V.If the resistance is not ideal, part of the common-mode voltage will be amplified by the differential amplifier and appear at VOUT as the effective voltage difference between V1 and V2, which cannot be distinguished from the real signal. The ability of the differential amplifier to suppress this part of the voltage is called  Common Mode Rejection  (CMR). This parameter can be expressed as a ratio (CMRR) or converted into decibels (dB).In an article published in 1991, Ramón Pallás-Areny and John Webster pointed out that assuming that the op amp is an ideal op amp, the common mode rejection can be expressed as:Among them, Ad is the gain of the difference amplifier, t is the resistance tolerance. therefore:In the case of unity gain and 1% resistance, CMRR is equal to 50 V/V (or about 34 dB);In the case of 0.1% resistance, CMRR is equal to 500 V/V (or approximately 54 dB);It is even assumed that the operational amplifier is an ideal device with unlimited common-mode rejection.If the common-mode rejection of the operational amplifier is sufficiently high, the total  CMRR is limited by resistance matching. Some low-cost op-amps have a minimum CMRR of 60 dB to 70 dB, making calculations more complicated.III Low Tolerance ResistanceThe first suboptimal design is shown in Figure 2.This design is a low-end current detection application using OP291. R1 to R4 are discrete 0.5% resistors. According to the formula in the article by Pallás-Areny, the optimal CMR is 64 dB.Fortunately, the common-mode voltage is very close to the ground, so CMR is not the main source of error in this application. A current sense resistor with a tolerance of 1% will produce a 1% error, but the initial tolerance can be calibrated or adjusted.However, since the operating range exceeds 80°C, the temperature coefficient of resistance must be considered.Figure 2. Low-end detection with high noise gainFor extremely low shunt resistance values, a 4-pin Kelvin sense resistor should be used. Using a high-precision 0.1 Ω resistor and directly connecting the resistor with a PCB trace of a few tenths of an inch can easily increase 10 mΩ, resulting in an error of more than 10%. But the error will be greater because the temperature coefficient of the copper traces on the PCB exceeds 3000 ppm.The shunt resistance value must be carefully selected. A higher value produces a larger signal. This is a good thing, but the power consumption (I2R) will also increase, possibly up to several watts. With a smaller value (mΩ level), the parasitic resistance of the line and PCB trace may cause a larger error. Generally, Kelvin detection can be used to reduce these errors.We can use a special four-terminal resistor (such as Ohmite LVK series) or optimize the PCB layout to use standard resistors. If the value is extremely small, PCB traces can be used, but this will not be very accurate.Commercial four-terminal resistors (such as Ohmite or  Vishay's products) may cost several dollars or more to provide 0.1% tolerance and extremely low temperature coefficient. A complete error budget analysis can show how to improve accuracy with the minimal cost increase.Regarding the problem of a large offset (31mV) with no current flowing through the sense resistor, it is caused by the "rail-to-rail" op amp being unable to swing all the way to the negative power rail (ground).However, the term "rail-to-rail" can be misleading: the output will be close to the power rail—much closer than the output stage of a classic emitter follower—but never actually reach the power rail. Rail-to-rail operational amplifiers have a minimum output voltage VOL, which is equal to VCE(SAT) or RDS(ON) × ILOAD.If the offset voltage is equal to 1.25 mV and the noise gain is equal to 30, the output is equal to: 1.25 mV × 30 = ±37.5 mV (35 mV due to the presence of VOS and VOL). Depending on the polarity of VOS, the output may be as high as 72.5 mV without load current.If the maximum value of VOS is 30μV and the maximum value of VOL is 8 mV, modern zero-drift amplifiers (such as AD8539) can reduce the total error to the level mainly caused by the sense resistor.IV Another Low-end Detection ApplicationAnother example is shown in Figure 3. This example has low noise gain, but it uses a low precision four-channel op amp with 3 mV offset, 10-μV/°C offset drift, and 79 dB CMR,  And in the range of 0 A to 3.6 A, an accuracy of ±5 mA is required. If a ±0.5% detection resistor is used, the required ±0.14% accuracy cannot be achieved. If a 100 mΩ resistor is used, a ±5 mA current can produce a ±500 μV voltage drop.Unfortunately, the offset voltage of an op amp with temperature is ten times greater than the measured value. Even if VOS is adjusted to zero, a temperature change of 50°C will exhaust the entire error budget. If the noise gain is 13, any change in VOS will be expanded by 13 times. To improve performance, zero-drift operational amplifiers (such as AD8638, ADA4051, or ADA4528), thin-film resistor arrays, and higher-precision sense resistors should be used.Figure 3. Low-end detectionV High Noise GainThe design in Figure 4 is used to measure high-side current, and its noise gain is 250. The maximum VOS rating of the OP07C operational amplifier is 150 μV. The maximum error is 150 μV × 250 = 37.5 mV. To improve performance, and ADA4638 zero-drift operational amplifier is used. The device has a nominal offset voltage of 12.5 μV over the temperature range of -40°C to +125°C.However, due to the high noise gain, the common-mode voltage will be very close to the voltage across the sense resistor. The input voltage range (IVR) of OP07C is 2 V, which means that the input voltage must be at least 2 V below the positive rail. For the ADA4638, IVR = 3 V.Figure 4. High-side current detectionVI Single Capacitor Roll-offThe example in Figure 5 is slightly more complicated. So far, all the equations are for resistance. But it is more accurate than they should take impedance into account. In the case of adding capacitance (whether it is deliberately added capacitance or parasitic capacitance), the AC CMRR depends on the impedance ratio at the target frequency. To roll off the frequency response in this example, you can add a capacitor C2 across the feedback resistor, as you would normally do in an inverting op-amp configuration.Figure 5. Try to create a low pass responseIf you need to match the impedance ratio Z1 = Z3 and Z2 = Z4, you must add capacitor C4. It is easy to buy 0.1% or better resistors on the market, but even 0.5% capacitors cost more than $1. The impedance at very low frequencies may not matter, but capacitance tolerance or a 0.5 pF difference between the two op amp inputs due to PCB layout can cause the AC CMR  to drop by 6 dB at 10 kHz. This is particularly important when using a switching regulator.Single-chip difference amplifiers (such as AD8271, AD8274 or AD8276) have much better AC CMRR performance. Because the two inputs of the operational amplifier are in a controlled environment on the chip, and the price is usually cheaper than a discrete operational amplifier and four precision resistors.VII Capacitance between Input Terminals of Op AmpIn order to roll off the response of the differential amplifier, some designers will try to add a capacitor C1 between the two op amp inputs to form a differential filter, as shown in Figure 6.This is feasible for instrumentation amplifiers, but not feasible for operational amplifiers. VOUT will move up and down through R2, forming a closed loop. At DC, this does not cause any problems, and the circuit behaves as described in Equation 2.As the frequency increases, the reactance of C1 decreases. The feedback into the input of the op amp decreases, causing the gain to increase. Eventually, the op amp will work in an open-loop state because the capacitor shorts the input.Figure 6. Input capacitance reduces high frequency feedbackOn the Bode plot, the open-loop gain of the operational amplifier drops at -20dB/dec, but the noise gain increases at +20dB/dec, forming a -40dB/dec crossover. As we know, it must oscillate. In general, never use capacitors between the inputs of an operational amplifier (except in rare cases, but this blog will not discuss it here).VIII ConclusionWhether it is a discrete or single chip, the four-resistor differential amplifier is widely used. In order to obtain a stable and production-worthy design, the noise gain, input voltage range, impedance ratio, and offset voltage specifications should be carefully considered. FAQWhat is the differential amplifier circuit able to do?Reduce the zero drift What is the differential amplifier circuit often used as?Multi-stage amplifiers What is one of important functions of the differential amplifier?Suppress the common mode signal of the two inputs.

The CD4511B BCD is a 7-segment Decoder Driver IC, which is similar to the type MC14511.CD4511BE Decoder DisplayCatalogProduct OverviewCD4511BE CAD ModelsCD4511BE Package DimensionsCD4511BE Functional DiagramCD4511BE FeaturesCD4511BE Product AttributesCD4511BE ApplicationsAlternate PartsComponent DatasheetCD4511BE vs MC14511BALDUsing WarningsCD4511BE ManufacturerFAQProduct OverviewCD4511BE Decoder DriverThe CD4511BE is a CMOS BCD to 7 segment LED latch decoder driver in 16 pin DIP package. It is constructed with CMOS logic and NPN bipolar transistor output devices on a single monolithic structure. This device combines low quiescent power dissipation and high noise immunity features of RCA CMOS with NPN bipolar output transistors capable of sourcing up to 25mA. This capability allows CD4511B to drive LED's and other displays directly. Lamp test, blanking and latch enable or strobe inputs are provided to test display, shut off or intensity modulate and store BCD code. Several different signals may be multiplexed and displayed when external multiplexing circuitry is used.The CD4511B types are supplied in 16-lead hermetic dual-in-line ceramic packages (F3A suffix), 16-lead dual-in-line plastic packages (E suffix), 16-lead small-outline packages (NSR suffix), and 16-lead thin shrink small-outline packages (PW and PWR suffixes).Texas Instruments Complex Function ICs from the 4000 Series CMOS Logic Family includes 7-segment LCD Latch/Decoder/Drivers, Magnitude Comparators and Phase Locked Loop (PLL) ICs.CD4511BE CAD ModelsCD4511BE Decoder CAD ModelsCD4511BE Package Dimensions✔️Package OutlineCD4511BE TSSOP Package (1.2mm)✔️Mechanical DataCD4511BE Ceramic Dual-in-Line Package CD4511BE Plastic Dual-in-Line Package CD4511BE Plastic Small-outline PackageCD4511BE Functional DiagramCD4511BE Functional Diagram CD4511BE Logic DiagramCD4511BE Features• High output sourcing capability up to 25mA• Supply voltage range from 3V to 18V• Input latches for BCD code storage• 100% tested for quiescent current at 20V• Maximum input current of 1µA at 18V (full package temperature range) and 100nA at 18V (25°C)• 5V, 10V and 15V parametric ratings• Operating temperature range -55°C to 125°CCD4511B Chip Dimensions and Pad LayoutCD4511BE Product AttributesSpecificationsValuesEU RoHSCompliantECCN (US)EAR99Part StatusActiveHTS8542.39.00.01Logic FamilyCD4000Logic FunctionLatch/Decoder/DriverNumber of Elements per Chip1Number of Element Inputs4Number of Input Enables per Element1Number of Element Outputs7Number of Output Enables per Element0PolarityNon-InvertingMaximum Propagation Delay Time @ Maximum CL (ns)300@15V|1040@5V|420@10VAbsolute Propagation Delay Time (ns)1320Process TechnologyCMOSMaximum Low Level Output Current (mA)4.2(Min)Minimum Operating Supply Voltage (V)3Typical Operating Supply Voltage (V)3.3|5|9|12|15Maximum Operating Supply Voltage (V)  1818Maximum Quiescent Current (mA)  0.10.1Propagation Delay Test Condition (pF)50Minimum Operating Temperature (°C)-55Maximum Operating Temperature (°C)125Supplier Temperature GradeMilitaryPackagingTubeSupplier PackagePDIPPin Count16Standard Package NameDIPMountingThrough HolePackage Height5.08(Max) - 0.51(Min)Package Length19.69(Max)Package Width6.6(Max)Package Thickness3.9 mmPCB changed16Lead ShapeThrough HoleLead FreeLead FreeRadiation HardeningNoREACH SVHCNo SVHCCD4511BE ApplicationsLED LightingAlternate PartsMC14511BALD, CD4511BF3A, MC14511BCPDComponent DatasheetCD4511BE PDFCD4511BE vs MC14511BALDSpecificationsCD4511BE MC14511BALDPbfree CodeYes*Rohs CodeYesNoPart Life Cycle CodeActiveObsoleteIhs ManufacturerTEXAS INSTRUMENTS INCMOTOROLA INCPart Package CodeDIP*Package DescriptionDIPDIPPin Count16*Reach Compliance CodecompliantunknownECCN CodeEAR99EAR99HTS Code8542.39.00.018542.39.00.01Samacsys DescriptionCMOS BCD-to-7-Segment LED Latch Decoder Drivers*Samacsys ManufacturerTexas Instruments*Family4000/14000/400004000/14000/40000Input ConditioningLATCHEDLATCHEDJESD-30 CodeR-PDIP-T16R-GDIP-T16JESD-609 Codee4e0Length19.305 mm19.3 mmLoad Capacitance (CL)50 pF50 pFLogic IC TypeSEVEN SEGMENT DECODER/DRIVERSEVEN SEGMENT DECODER/DRIVERMax I(ol)0.0015 A*Number of Functions11Number of Terminals1616Operating Temperature-Max125 °C125 °COperating Temperature-Min-55 °C-55 °COutput PolarityTRUETRUEPackage Body MaterialPLASTIC/EPOXYCERAMIC, GLASS-SEALEDPackage CodeDIPDIPPackage ShapeRECTANGULARRECTANGULARPackage StyleIN-LINEIN-LINEPacking MethodTUBE*Peak Reflow Temperature (Cel)NOT SPECIFIEDNOT SPECIFIEDPower Supply Current-Max (ICC)3 mA*Prop. Delay@Nom-Sup420 ns*Propagation Delay (tpd)1320 ns1440 nsQualification StatusNot QualifiedNot QualifiedSeated Height-Max5.08 mm4.19 mmSupply Voltage-Max (Vsup)18 V18 VSupply Voltage-Min (Vsup)3 V3 VSupply Voltage-Nom (Vsup)5 V5 VSurface MountNONOTechnologyCMOSCMOSTemperature GradeMILITARYMILITARYTerminal FinishNickel/Palladium/Gold (Ni/Pd/Au)Tin/Lead (Sn/Pb)Terminal FormTHROUGH-HOLETHROUGH-HOLETerminal Pitch2.54 mm2.54 mmTerminal PositionDUALDUALTime@Peak Reflow Temperature-Max (s)NOT SPECIFIEDNOT SPECIFIEDWidth7.62 mm7.62 mmBase Number Matches22Using WarningsPlease check their parameters and pin configuration before replacing them in your circuit.CD4511BE ManufacturerTexas Instruments Inc. (TI) is an American technology company that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally. Its headquarters are in Dallas, Texas, United States. TI is one of the top ten semiconductor companies worldwide, based on sales volume. Texas Instruments's focus is on developing analog chips and embedded processors, which accounts for more than 80% of their revenue. TI also produces TI digital light processing (DLP) technology and education technology products including calculators, microcontrollers and multi-core processors.FAQWhat package is the CD4511BE?16 pin DIP What type of structure is the CD4511BE constructed with?Monolithic What does CD4511B do?Drive LEDs and other displays

I. IntroductionThe heart rate is a key indicator value reflecting the health of the body. Simply put, the heart rate refers to the frequency of cardiovascular beats within 1 minute. The test of heart rate can show scientific evidence in work such as disease diagnosis, patient care, and athlete training. In recent years, many medical types of equipment and fitness equipment developed and manufactured by countries around the world have adopted heart rate test power circuits. The low cost of product development and high-performance heart rate test power circuits have important application values. The article introduces this kind of heartbeat rate detection system based on AD620 integrated IC in detail. Using the excellent low-noise characteristics of AD620 integrated IC, plus effective filtering and amplifying circuits, combined with microprocessor solutions, a high-precision heart rate monitoring system is obtained.Figure 1 AD620CatalogI. IntroductionII. AD620 ChipIII. Circuit Design3.1 Block Diagram3.2 Signal Extraction Circuit Based on AD6203.3 Filter Amplifier Circuit3.4 Microprocessor Circuit3.5 Experimental Results and DiscussionIV. ConclusionFAQOrdering & Quantity II.AD620 chip AD620 is a low-cost, high-precision instrumentation amplifier. It only needs an external resistor to set the gain, and the gain range is 1 to 10000. In addition, AD620 adopts 8-pin SOIC and DIP package, the size is smaller than the discrete circuit design, and the power consumption is lower, so it is very suitable for battery-powered and portable applications. Its characteristics are as follows: EASY TO USE　　Gain Set with One External Resistor　　(Gain Range 1 to 10,000)　　Wide Power Supply Range (±2.3 V to ±18 V)　　Higher Performance than Three　　Op Amp IA Designs　　Available in 8-Lead DIP and SOIC Packaging　　Low Power, 1.3 mA max SupplyLOW NOISE　　9 nV/√Hz, @ 1 kHz, Input Voltage Noise　　0.28 µV p-p Noise (0.1 Hz to 10 Hz)EXCELLENT DC PERFORMANCE (B GRADE)　　50 µV max, Input Offset Voltage　　0.6 µV/°C max, Input Offset Drift　　1.0 nA max, Input Bias Current　　100 dB min Common-Mode　　Rejection Ratio (G = 10)EXCELLENT AC SPECIFICATIONS　　120 kHz Bandwidth (G = 100)        15 µs Settling Time to 0.01% III. Circuit Design 3.1 Block Diagram The surface of the human skin contains human ECG,  EMG, and power frequency signals. Generally, the noise of the ECG  signal containing heart rate information is much smaller than that of the power frequency signal. In order to extract the weak ECG  signal, a low-noise operational amplifier must be used and a reasonable filter amplifier circuit must be designed. Figure 2 is a block diagram of the heart rate detection system. The whole heart rate detection system consists of four parts: the sensor head in contact with the human skin surface, the signal extraction circuit, the filter amplifier circuit, and the microprocessor circuit. The sensor head is generally a metal that is easy to conduct electricity. After contacting the surface of the human skin, it has complex electrical signals such as human ECG  signals, electromyographic signals, and power frequency signals. We use the low-noise AD620 operational amplifier as the core chip of the heartbeat rate extraction circuit. In the filtering and amplifying circuit part, a simple low-pass filtering circuit is used. The experimental results show that this filtering circuit is sufficient to extract the heart rate signal. After filtering the amplified signal, an adjustable comparator combined with a transistor circuit is used to form a 5 volt TTL level signal, and finally connected to the microprocessor, the heartbeat signal is processed by the microcomputer, and the heartbeat rate is calculated and displayed.Figure 2 Block diagram of heart rate detection principle 3.2 Signal Extraction Circuit Based on AD620 AD620 operational amplifier, usually used in high-precision test instruments, the maximum nonlinear error of 40ppm, the maximum voltage offset of 50uV, the maximum temperature drift of 0.6uV/℃, because of its low noise, low bias current, low power consumption characteristics, it is widely used in medical fields such as electrocardiogram (ECG) and blood pressure monitoring. Figure 3 is a signal extraction circuit based on AD620, in which the LEFT_ARM, RIGHT_ARM, LEG three leads are connected to the aluminum sheet (ie the sensor head), which are respectively connected to the left and right hands and right feet of the human body. Our experimental research results show that the R4 gain of LEFT_ARM is 1K, the corresponding AD620 operational amplifier gain is 50. Too much gain will weaken the final signal-to-noise ratio, so the R4 resistance value should be set reasonably in the experiment. The 0.1uF capacitance between the LEFT_ARM and RIGHT_ARM leads is to effectively weaken the power frequency noise. The LEG lead is connected to AD620 through TL082A, which provides the reference potential of the human body for the differential signal of LEFT_ARM and RIGHT_ARM.Figure 3 Signal extraction circuit based on AD620 3.3 Filter Amplifier Circuit Figure 4 is a filter amplifier circuit. Three operational amplifiers constitute a three-stage amplification, each amplifying 100 times. Due to circuit loss, especially the loss of the isolation capacitor, the actual signal amplification is less than 1 million times. The ratio of the resistance values of R6 and R5, R9 and R8, R11 and R10 in the circuit determines the magnification factor, and these resistance values should be adjusted reasonably in practical applications. A low-pass filter circuit should be used while amplifying the signal to achieve the effect of filtering power frequency noise. Since the frequency of the power frequency noise is 50Hz, the designed filter circuit has a passband bandwidth of less than 50Hz, that is, the RC time constant of the capacitor resistor must be of the same order of magnitude as the power frequency signal period. R7 and C10 in the circuit form a low-pass filter. We use 1uF capacitor isolation between levels of amplification. These capacitors will attenuate the signal at the same time, and the three operational amplifiers are selected for signal amplification, so the signal-to-noise ratio is improved. It should be pointed out that if the isolation capacitor is too large, it is easy to cause the output electrical signal to drift.Figure 4 Filter amplifier circuit Figure 5 is the shaping circuit. The heartbeat rate signal and signal-to-noise ratio of the 2ND_OUT lead are large enough (the pulse rate of the heartbeat rate is 1 ~ 5V), after the half-wave shaping of D1, then the adjustable comparator, and finally the transistor Q1 is converted to the microcontroller level.Figure 5 Shaping circuit 3.4 Microprocessor Circuit The final signal is processed by AT89C51, and the heart rate is displayed by an LED digital tube. The microprocessor circuit with AT89C51 as the core is very mature, so it's no need to repeat it here. 3.5 Experimental Results and Discussion Figure 6 shows the actual measurement results of the human heart rate using the above system. Figure 6(a) is the voltage signal after the signal 2ND_OUT is shaped by D1. It can be seen from the figure that this is actually a complete ECG  signal. In a cycle of signals, there are two more obvious pulse signals. This pulse characteristic varies from person to person. It is found that there is at least one pulse signal through actual measurement of the ECG  signals of different people. Figure 6(b) shows the electrical signal of  HEART_PULSE, which is obtained after the signal of Figure 6(a) passes through the comparator and the transistor switch. The signal can be directly input to the port of the microprocessor, and the microprocessor calculates and outputs the heart rate.Figure 6 Heart rate signal diagram When developing the above-mentioned heart rate detection system, there are several key points to pay special attention to: (1) Connecting capacitors to LEFT_ARM and RIGHT_ARM can greatly improve the signal-to-noise ratio; the main energy of the heart rate signal on LEFT_ARM and RIGHT_ARM is at a frequency of about 1 Hz, and the capacitor is a low-pass filter that can filter and suppress noise; Choose a large capacitor to eliminate high-frequency noise. In the experiment, a 10uF non-polar capacitor is used, and the effect is very good; (2) The low-pass filter circuit effectively weakens the power frequency signal and improves the signal-to-noise ratio; it adopts a combination of active filtering and passive filtering to filter while amplifying, which has a better effect than filtering after amplification; (3) Capacitor isolation attenuation and multi-stage amplification are beneficial to improve the signal-to-noise ratio; the main noise is 50Hz power frequency signals. Although the multi-stage amplification and filtering increase thermal noise, it has great suppression of power frequency noise. Of course, the number of amplification stages cannot be infinite, and the best number of stages is the minimum sum of power frequency noise and thermal noise; (4) Small capacitor isolation should be used to suppress DC signal drift. This is shown by the experimental results, and the reason needs to be further studied. IV. Conclusion This article discusses a scheme based on AD620 chip heart rate detection and introduces the circuit design of the sensor head, signal extraction, filter amplification, and microprocessor that make up the system. Gives the method to improve the system performance. Experiments show that the system can obtain better ECG signals and accurate heart rates. The heartbeat rate detection system in this article has strong anti-interference ability, simple structure, and low cost.FAQWhat is obtained using the low-noise characteristics of AD620 integrated IC?High-precision heart rate monitoring systemWhat package does AD620 adopt?8-pin SOIC and DIPWhat type of test instruments are AD620 operational amplifier usually used?High-precision test instrumentsWhat is AD620?AD620 is a low-cost, high-precision instrumentation amplifier. It only requires an external resistor to set the gain. The gain range is 1 to 10,000.Can I change AD620 to AD623 when making MCU products?Both AD620 and AD623 are single instrumentation amplifiers, and the pin arrangement is exactly the same.The main difference is: AD620 must use positive and negative power supplies, AD623 can be a positive and negative power supply or a single power supply.If the original board is AD620, you can replace it with 623; if the original board is AD623, you may not be able to replace it with 620 (it depends on whether the power supply of the original board circuit is dual power supply or single power supply).After replacing AD620 and AD623 in single-chip products, the program can work normally without modification.What is the difference between AD620BR and AD620AN?Their packages are different.What is the output resistance of AD620? How to adjust it?AD620 is a kind of low power consumption instrument amplifier, its output resistance is about 10K, this is the inherent characteristic of this chip, generally it is difficult to adjust.If you have requirements for output resistance, you can generally use an external circuit to solve it.Is AD620 a positive phase amplification or a reverse phase amplification?AD620 is an instrument amplifier, the output voltage is [(Vin+)-(Vin-)]*gain.If the desired signal is (Vin+)-(Vin-), the gain is positive, which is equivalent to positive amplification.Conversely, if the desired signal is (Vin-)-(Vin+), the gain is equivalent to negative, which is equivalent to reverse amplification.What is an instrumentation amplifier?Instrumentation amplifier, an improvement of the differential amplifier, has an input buffer, does not require input impedance matching, so that the amplifier is suitable for measurement and electronic instruments

I DescriptionThis blog introduces and analyzes 4 simple and easy 74LS00 Nand Gate circuit diagrams. It’s including Square Wave Generator Circuit, Pulse Generator Circuit, LED Light Circuit. And in the end, we will analyze the circuit that turns the timer into a countdown timer in detail.This Video is An Introduction of 7400 Logic DevicesCatalogI DescriptionII Square Wave Generator CircuitIII Pulse Generator CircuitIV LED Light CircuitV Turn Timer into Countdown Timer5.1 Scheme Design5.2 Implementation of Scheme DesignFAQOrdering & QuantityII Square Wave Generator CircuitLet’s take a look at the figure below. It’s a square wave generator circuit. This circuit contains a 74LS00 Nand Gate integrated circuit. Figure 1. Square Wave Generator Circuit Diagram Among this circuit diagram:NAND gates 1, 2, and external RC time constant components form an oscillator circuitNAND gate 3 is a buffer output stage.As long as the capacity of C is changed, square wave outputs of different frequencies can be obtained.III Pulse Generator CircuitFigure 2. Pulse Signal Generator Circuit DiagramThe circuit diagram is shown in Figure 2 and it’s a simple pulse signal generator circuit. The signal generator mainly uses two TTL integrated circuits (74LS00 and 74LS221 ). So why choose these two circuits? That is because these two circuits can be used to generate a pulse signal of τ=4μs. Besides, it uses fewer components and is convenient for debugging and maintenance.IV LED Light CircuitThis circuit is made with  NE555, 74LS00, 74LS154, 74LS193, and LED lights, and the production process is very simple. When we turn on the power, here is how it works is:When the output Q0 of the 74LS154 decoder is low, the 74LS193  is a positive counter. At this time, the LEDs are individually lit from D1...D16;When the output Q15 of the 74LS154 decoder is low, the 74LS193  is a countdown counter. At this time, the LEDs are individually lit from D16...D1.Figure 3. LED Light Circuit DiagramFrom the above we can see that: the LED lights turn on from D1 to D16, and then back to D1 from D16, and so on.V Turn Timer into Countdown TimerGenerally, there are two design ideas for turning a timer into a countdown timer: First, change the counting chip in the timer; Second, reset the function of the chip.Besides, there is actually another way to achieve this goal: By applying the 74LS00 and 74LS20 chips to "reverse" the results on the display, so as to achieve the purpose of counting down.5.1 Scheme DesignThe result displayed by each digit of the timer is an incremental value, such as 0.1.2.3.4.5.6.7.8.9. Yet, the countdown timer displays a decreasing value, such as 9.8.7.6.5.4.3.2.1.0. As long as the display result conversion is completed with a suitable logic circuit, the timer can be turned into a countdown timer.At first, we need to find the logical relationship between the timer display result and the countdown timer display result. Table 1 below lists the BCD codes corresponding to each display result of the timer and countdown timer. From this table, you can easily find the BCD codes of the timer and countdown timer:The lowest bit Q1 and Y1 are opposite; While Q2 and Y2 are the same;Relationship between Q3 and Y3: Y3 of the countdown timer is the exclusive OR of timer Q3 and Q2;Relationship between Q4 and Y4: The Y4 bit of the countdown timer is the opposite value of the OR of Q4, Q3, and Q2 of the timer, which is also equal to the non-re-AND of Q4, Q3, and Q2.Table 1. Corresponding BCD Code Displayed by (Down)Timer  The above logical expression is:Therefore, as long as you choose a circuit that can complete the above logic conversion relationship, you can realize the design from a timer to a countdown timer. The figure? shows a two-digit timer circuit. After adding the above conversion circuit, it becomes figure 3 shows the countdown circuit. Figure 4. Timer Circuit Displaying 2 Digits Figure 5. Countdown Circuit Diagram5.2 Implementation of Scheme DesignTwo kinds of chips 74LS00 and 74LS20 are used here. The former are four two-input NAND gates, which are used to complete the conversion of Y1 and generate the negation of Q4, Q3, and Q2. The latter are two four-input NAND gates, which are used to obtain Y4 from the non-reAND of Q4, Q3, and Q2. In summary, we can follow the logical relationship as follows:   The logic diagram is shown in Figure 6.Figure 6. Logic DiagramKnowing that the XOR gate operation can be completed, the Y3 conversion can be completed. The connection circuit diagram of the above-mentioned Y4, Y3, Y1 conversion specific physical objects is shown in Figure 7. Figure 7. Y4, Y3, Y1 Conversion Specific Physical Connection DiagramFigure 8 shows the actual picture of the countdown timer.Figure 8. Countdown TimerSo far, the timer has become a countdown timer. Through this design method, there is no need to change the original counter circuit, is it particularly trouble-free? FAQ1.What is a 74LS00?74LS00 is NAND gates-based IC. It has 14 pins which all connected with 4 NAND gates. Due to the NAND gate known as universal gate, 74LS00 can be converted into OR and NOT gate easily. The IC comes in three packages, SOIC, PDIP, and SOP. 2.What is NAND logic gate?In digital electronics, a NAND gate (NOT-AND) is a logic gate which produces an output which is false only if all its inputs are true; thus its output is complement to that of an AND gate. 3.What is a 74LS08?74LS08 is a Quadruple 8-bit Two Input AND IC. Gate AND gate is a digital circuit used to convert the logic state to a specific logic. In AND gate two logics state signals are used.