The Kynix Blog - Transmitters

IntroductionThink about the modern embedded systems around you—your smartphone, smartwatch, or even the smart appliances in your home. These devices are constantly exchanging information in the background, working together to deliver the seamless experiences we have all come to expect. At the core of this communication lies the Universal Asynchronous Receiver Transmitter, or UART.UART is a key player in serial communication for many embedded applications. It converts parallel data into serial form for transmission and then back to parallel form for processing. This guide will walk you through everything you need to know about UART, from its basics to its real-world applications, advantages, and limitations.Whether you're an engineer working on embedded system designs, a hobbyist tinkering with microcontrollers, or simply someone interested in understanding serial communication, this guide will help you get to grips with the fascinating world of UART. What is a UART?The Universal Asynchronous Receiver Transmitter (UART) is a hardware component or module that facilitates serial communication by converting parallel data into serial form. Unlike synchronous protocols, UART doesn’t need a clock signal to synchronize data transmission between devices. Instead, it relies on start and stop bits to signal the beginning and end of a data transmission, making it both simple and versatile.UART is composed of two main parts: the transmitter and the receiver. The transmitter takes parallel data and sends it serially over a communication line, while the receiver collects the incoming serial data and converts it back into parallel form for the device to process. How Does UART Work?To understand how UART works, we need to explore how it transmits and receives data. UART works by breaking down parallel data into a sequence of bits, which are then transmitted serially. Each byte of data is preceded by a start bit, followed by the data bits, an optional parity bit for error checking, and concluded with one or two stop bits.The start bit signals the beginning of a transmission, usually involving a transition from a high voltage (idle state) to a low voltage. The data bits are then transmitted—generally 5 to 9 bits, depending on the configuration. The optional parity bit helps detect errors during transmission, while the stop bit marks the end of the data packet.On the receiving end, the UART module interprets these bits by identifying the start bit, reading the data bits, verifying the parity, and checking for the stop bit. This process enables reliable communication between devices with minimal complexity. Key Features of UARTAsynchronous Communication: Unlike SPI or I2C, UART does not need a clock signal, which makes it easier to implement and less resource-intensive.Simple Interface: UART requires just two signal lines for communication—one for transmitting data (TX) and one for receiving data (RX).Configurable Baud Rate: The speed of communication, defined as the baud rate, is adjustable. Common baud rates include 9600, 115200, and others, making UART flexible for different applications.Error Detection: The optional parity bit allows for basic error detection, which is useful in environments where data integrity is crucial. Applications of UARTUART is extensively used in embedded systems and serves as a communication bridge between microcontrollers and peripherals. Here are some common applications of UART:Microcontroller to PC Communication: UART is often used to establish communication between microcontrollers and PCs. This is commonly done through USB-to-UART converters, which are great for debugging or data logging purposes.Bluetooth Modules: Many Bluetooth modules, like the HC-05 and HC-06, use UART to communicate with microcontrollers, providing an easy way to add wireless capabilities to projects.GPS Modules: GPS modules typically use UART to output serial data, which microcontrollers can then read to get location information.Debugging and Diagnostics: UART is a popular choice for debugging in embedded systems. By connecting the UART port to a serial console, developers can monitor the system’s behavior, making it easier to diagnose issues. Comparing UART with Other Serial Communication ProtocolsUART is just one type of serial communication protocol, and it’s important to know when to use it compared to other options like SPI and I2C.SPI (Serial Peripheral Interface): SPI is a synchronous communication protocol that requires a clock signal. It’s faster than UART and ideal for high-speed data transfer, but it requires more signal lines and doesn’t easily support multiple devices on the same bus.I2C (Inter-Integrated Circuit): I2C is another synchronous protocol that uses two lines (SCL and SDA) for communication. It supports addressing, which makes it better suited for connecting multiple devices. However, it has more overhead compared to UART and requires careful timing.In summary, UART is simpler to implement and well-suited for point-to-point communication where speed isn’t a critical factor. It’s a great choice for applications with minimal device connections. Advantages of UARTEase of Implementation: UART is straightforward to set up, with simple hardware requirements and minimal software configuration.Low Cost: With only two wires needed for communication, UART is cost-effective in terms of both hardware and design complexity.Flexible Baud Rate: UART allows for adjustable baud rates, providing flexibility when connecting devices with different communication speed requirements. Limitations of UARTShort Distance Communication: UART is not ideal for long-distance communication as the signal can degrade over extended cables, leading to data corruption.Point-to-Point Limitation: UART is generally limited to point-to-point communication. It’s not designed for multi-device communication without additional hardware.Speed Constraints: Compared to protocols like SPI, UART operates at slower speeds, making it unsuitable for high-speed data transfers. Choosing the Right UART ConfigurationChoosing the right UART configuration for your project involves several considerations:Baud Rate: Ensure that both devices use the same baud rate to prevent data errors.Parity Bit: Determine whether error detection is needed. Adding a parity bit can help detect transmission errors, enhancing reliability.Number of Stop Bits: Depending on the required reliability, you can choose between one or two stop bits. Two stop bits provide greater reliability but reduce the overall data rate.Flow Control: For higher data rates, consider implementing hardware flow control (RTS/CTS) to prevent data loss when the receiver cannot keep up with the incoming data. Real-World Example: UART in Microcontroller ProjectsA common use of UART is in microcontroller projects involving peripheral modules like GPS, Bluetooth, or Wi-Fi. For example, when building a GPS tracker, the GPS module typically communicates its location data to a microcontroller via UART. The microcontroller can then process this data and send it to another module, such as a Bluetooth transmitter, to relay the location to a smartphone.Another practical application is debugging firmware for IoT devices. By connecting the UART to a USB-to-serial converter, debug messages can be sent from the device to a PC terminal, helping developers understand what the firmware is doing in real-time and diagnose any issues. ConclusionThe Universal Asynchronous Receiver Transmitter (UART) is an essential component in embedded systems, providing a reliable, low-cost means for serial communication. Its ease of use and flexible baud rate make it a popular choice for a wide range of applications, including debugging, data transmission, and peripheral integration.While UART has its limitations—such as being point-to-point and having slower data transfer speeds compared to other protocols—its simplicity and effectiveness make it indispensable in many embedded projects. By understanding how UART works and knowing when to use it, you can design better, more reliable systems and appreciate the intricacies of serial communication.Ready to explore more? At Kynix Electronic, we offer a range of components, including UART modules and integrated circuits, to meet your embedded system needs. Visit our site today and discover the perfect components to kickstart your next project with confidence!

IntroductionIn the world of electronics, temperature control and circuit protection are crucial, especially as devices become more complex and sensitive. PTC thermistors, or Positive Temperature Coefficient thermistors, are essential components in managing these requirements. Found in everything from home appliances to automotive systems, these small but powerful resistors are designed to respond to temperature changes, protecting circuits and ensuring consistent performance.Whether you're an electronics engineer, a tech enthusiast, or simply curious about these critical components, this article will take you through everything you need to know about PTC thermistors, their types, applications, and why they’re indispensable in modern electronic design. What Exactly is a PTC Thermistor?PTC thermistors are temperature-sensitive resistors that react to heat in a unique way: as the temperature rises, their resistance increases. Unlike other resistors that maintain a constant resistance, PTC thermistors are specifically designed to change resistance based on the surrounding temperature. This characteristic makes them ideal for applications that require precise temperature monitoring, control, or protection against overheating.In technical terms, PTC thermistors experience an exponential rise in resistance after reaching a certain threshold temperature, known as the Curie point. This property allows them to serve as temperature sensors or as resettable fuses in circuits, helping to prevent damage from excessive heat or current surges. How Do PTC Thermistors Work?To understand how PTC thermistors function, it's important to look at their basic working principle.1.At lower temperatures, the thermistor behaves similarly to a standard resistor, with relatively low resistance.2.As the temperature approaches the Curie point, the resistance begins to increase more sharply.3.Once the Curie point is exceeded, the resistance rises dramatically, which can either slow down or stop current flow through the circuit. This behavior makes PTC thermistors useful in applications where protection from overheating or overcurrent is essential. By acting as a thermal "fuse," they ensure circuits don't overheat and sustain damage, offering a level of protection critical for the longevity of many devices. Why PTC Thermistors are Important in Modern Electronics1.Protecting Devices from OverheatingIn consumer electronics, industrial machinery, and vehicles, overheating is a common risk. PTC thermistors prevent damage by cutting off the current when the temperature rises beyond a safe limit, effectively acting as self-resetting fuses. Unlike traditional fuses, which need to be replaced after a fault, PTC thermistors "reset" once they cool down, making them a more sustainable solution. 2.Reliable Temperature SensorsDue to their sensitivity to temperature changes, PTC thermistors are widely used in thermostats, climate control systems, and various industrial applications that require consistent temperature monitoring. They can quickly detect shifts in temperature, sending feedback to control systems to adjust heating, cooling, or other temperature-related parameters. Types of PTC ThermistorsNot all PTC thermistors are created equal. They are primarily divided into two main types, each serving different purposes in electronics:Silistor PTC ThermistorsDescription: Silistor thermistors have a gradual increase in resistance with temperature, providing a more linear response curve.Ideal Applications: They are commonly used in applications that need temperature compensation, such as analog circuits and temperature-sensing devices. Silistor thermistors provide steady, predictable resistance changes, making them excellent for accurate temperature readings and adjustments. Switching PTC ThermistorsDescription: Switching PTC thermistors exhibit a steep increase in resistance once they reach a specific threshold temperature. After this point, their resistance rises sharply, almost like flipping a switch.Ideal Applications: Switching PTC thermistors are widely used in circuit protection and overcurrent applications. They can limit or cut off the current entirely when temperatures reach critical levels, which is especially useful in motor controls, transformers, and power supplies that may experience sudden surges. Choosing the Right PTC Thermistor for Your ApplicationSelecting the right PTC thermistor can seem overwhelming, but it largely depends on understanding your application’s needs and conditions.Determine Your Temperature RangeDifferent PTC thermistors are designed for different temperature ranges. For instance, if you're designing a circuit for an environment with high temperatures, look for thermistors that can maintain stable performance across that range without degradation.Response TimeSome applications require rapid response to temperature changes, such as safety-critical systems in automotive or industrial equipment. Thermistors with faster response times are necessary in these cases to ensure immediate protection.Physical Space ConstraintsFor compact designs or portable electronics, space can be a limiting factor. Small-sized thermistors, often surface-mounted, are ideal for such projects. Switching thermistors, known for their compact design, are particularly useful when space is at a premium. Key Specifications to Consider When Selecting PTC Thermistors Curie TemperatureThe Curie temperature, sometimes called the switching temperature, is the point at which the thermistor's resistance dramatically increases. This is a critical specification for PTC thermistors, as it determines the temperature range within which the thermistor can reliably operate. Resistance ToleranceAll thermistors have a tolerance range, meaning their actual resistance may vary slightly from the specified value. For high-precision applications, selecting a thermistor with a narrow tolerance range ensures consistency and accuracy. Current RatingThe current rating is the maximum current the thermistor can handle without damage. It’s essential to ensure that your thermistor's current rating aligns with your circuit's needs to avoid potential overheating and malfunction. Applications of PTC Thermistors in Real-World ScenariosAutomotive ElectronicsPTC thermistors play a vital role in automotive electronics, from engine temperature monitoring to battery management systems. Their ability to prevent overheating makes them invaluable in an industry where safety and reliability are top priorities. In electric vehicles, PTC thermistors also contribute to battery protection, helping maintain optimal temperatures to extend battery life and performance.Household AppliancesMany household appliances rely on PTC thermistors for temperature control and safety. In washing machines, they can regulate water temperature, while in dryers, they help prevent overheating by limiting the temperature to safe levels. This feature not only enhances safety but also prolongs the appliance's operational life.Telecommunication SystemsIn telecommunications, PTC thermistors are used to protect sensitive electronics within networking hardware. These thermistors help maintain consistent operation by preventing excessive heat build-up, which could lead to component failure in critical systems like routers and signal amplifiers. Understanding PTC Thermistor Theory and CalculationsFor those interested in the technical side, let's dive into the mathematical relationship behind PTC thermistors. The resistance of a PTC thermistor at a specific temperature can be estimated using the formula: R(T)=R0​⋅e^β(T−T0​)where:R(T) is the resistance at temperature T,R0 is the resistance at the reference temperature T0,β represents the material's thermal coefficient.This equation illustrates how the resistance of a PTC thermistor increases with temperature. By selecting a thermistor with the right β\betaβ value, you can tailor the thermistor's response to match the needs of your circuit. Practical Tips for Engineers Using PTC ThermistorsRegular Testing and MaintenanceLike all electronic components, PTC thermistors can degrade over time. Routine testing, especially in industrial and automotive applications, helps ensure they operate within their intended resistance range. Using Thermistor Selection ToolsMany manufacturers provide online selection tools to help you choose the right PTC thermistor based on your specific requirements. These tools often allow you to input desired parameters such as temperature range, tolerance, and current rating, simplifying the selection process. Designing for Temperature ExtremesIn environments subject to temperature fluctuations, choose PTC thermistors with a broader operating range or ones designed specifically for extreme conditions. This foresight can prevent performance issues and potential damage to the circuit. Real-World Considerations for PTC ThermistorsAlthough PTC thermistors are reliable components, they aren’t immune to real-world challenges. For example, factors like humidity and extreme temperatures can impact performance. If you're designing for an environment where these factors come into play, it’s essential to consider the thermistor's material composition and enclosure.In addition, thermistors exhibit slight resistance variations, even within their tolerance range. If your application requires ultra-precise performance, consider using thermistors with a tighter tolerance specification. This extra level of accuracy helps maintain the consistency and reliability of high-performance circuits. ConclusionPTC thermistors are essential components in the design of temperature-sensitive and protective electronic circuits. Their versatility, from acting as resettable fuses to serving as accurate temperature sensors, makes them an indispensable choice for engineers across multiple industries.By understanding the fundamentals of PTC thermistors, their different types, and their specific applications, engineers can harness these components to create safer, more reliable devices. Whether you’re designing for automotive, telecommunications, or consumer electronics, PTC thermistors offer both safety and functionality that elevate your designs to meet modern performance standards.

IntroductionWhat is RS485?MaterialsMAX485 pinoutHalf duplex operationHere is how the program worksFull duplex operationHalf duplex operation codeFull duplex codeIntroductionIn digital computer communication between two computers can be made using either parallel or serial method. In parallel communication separate line is dedicated for a one-bit information to transfer. This communication is fast and easy, but it requires a lot of wires at least as many as the number of bits need to be sent in parallel. For example, to transfer a 64-bit data from one device to another, 64 data lines will be required which is impractical in embedded systems. The alternative method to transfer data is to use serial communication. In serial communication one bit at a time is transferred from one device to another one. While this method solves the wiring problem it has a lot of other problems such as bandwidth, data lagging, complex protocol, and electrical standards. There are lot of different methods to do serial communication while one method is good in one situation another one is better in another situation. In this article we will discuss RS485 communication protocol which is one of the many available serial communication methods.Materials1MAX485 module2STM32 F401CDU6What is RS485?An industry specification called RS-485 outlines the physical layer and electrical interface for point-to-point electrical device communication. RS485 is the industrial standard for communication that defines the electrical interface and physical layer for point-to-point communication. RS485 is a robust communication system it can support multiple devices on a single bus, works in a noisy environment as well and requires a maximum of 4 lines.RS485 was first developed in 1983 and has since been used in many industrial applications because of its robustness and simplicity. It has the ability to transmit data over long distances while at the same time it is cheap, thus engineers are using it in all sorts of applications such as automotive, manufacturing, and theater spaces. Nowadays almost all motor controllers, VFDs and manufacturing machines will have a port available for RS485.RS485 is actually a standard that defines the electrical characteristics of the transmitters and receivers for communication protocols. RS482 uses two lines usually called A and B which must be balanced and differential. It means that the two lines must have same impedance, nearly same length and must be differential. The key features of RS485 communication are given belowMultipoint operation10 Mbps data transfer rate at 40 feet lengthMaximum cable length is 4000 feetRS485 works both in half duplex as well full duplex mode. In half duplex mode one device can either transmit or receive data at a time. While in full duplex mode, a device can transmit and receive data at the same time. Having more than one device on a bus can cause problem when two or more devices transmit data at the same time. Therefore, software control is necessary to ensure only one device transmit data at a time.RS485 is the physical layer of communication in the OSI model. It means this layer can be used as a base for other protocols such as UART which in most application people use because UART is an asynchronous communication protocol that does not require any clock signal which make it very easy to use. In this article we will demonstrate how RS485 can be used between two STM32 microcontrollers to communicate and exchange data. We will be using MAX485 module which is an easily available RS485 module. MAX485 pinoutRO → Receiver outputRE → Receiver enableDE → Data enableDI → Data inputVCC → Input voltageGND → GroundA, B → RS485 differential linesHalf duplex operationIn half duplex operation either data can be received or transmitted at a time. Both operations cannot be done at the same time. MAX485 has data flow control pins called DE and RE which puts the module in receiver mode or in transmit mode. Making them low puts the module in receiving mode while making them high puts the device in transmitter mode.In CubeMX the microcontroller of our choice is selected which in our case is STM32 F401CDU6. In connectivity UART1 should be enabled with 115200 bps baud rate. Other necessary settings are given below.RCC → Crystal/Ceramic ResonatorSYS → Debug → Serial WireClock Configuration → HCLK → 84 MHzClock Configuration → PLL Source Mux → HSEGPIO A7 is set as outputHere is how the program worksThe setup has two microcontrollers. We will call one side as A and the other side as B. When a user presses the user key on A STM32 microcontroller it will send the information to the B microcontroller via RS485. The receiving B microcontroller will switch on the onboard LED and will responds with an OK message. The OK message will blink the led on A microcontroller twice. Similarly, when the user presses key on B microcontroller it will transmit a message to A microcontroller and turns on the onboard LED and will responds with an OK message. The OK message will blink LED on B microcontroller twice. Similarly pressing the button again will do the same except this time it will turn off the LED.Full duplex operationIn full duplex operation data can be received or transmitted at the same time. Both operations can be done at the same time. In this mode two MAX485 modules will be required at each end and overall, 4 MAX485 modules will be used. It means that the two MAX485 modules will be constantly in receiving mode while the other two will constantly in transmission mode. MAX485 has data flow control pins called DE and RE which puts the module in receiver mode or in transmit mode. We will put the data control pins of two module as high while put the data control pins of other two module low. The configuration is shown below.The program works the same way as it was working in the half duplex mode however, this time the transmitted and received by MCUs at the same time.Half duplex operation code#include "main.h" UART_HandleTypeDef huart1; /* USER CODE BEGIN PV */int8_t R_Data[1] = {0};int8_t T_Data[1] = {69};/* USER CODE END PV */ /* Private function prototypes -----------------------------------------------*/void SystemClock_Config(void);static void MX_GPIO_Init(void);static void MX_USART1_UART_Init(void); int main(void){   HAL_Init();   SystemClock_Config();     MX_GPIO_Init();  MX_USART1_UART_Init();  /* USER CODE BEGIN 2 */  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);   //Put RS485 module in receiving mode  HAL_GPIO_WritePin(GPIOC, GPIO_PIN_13, GPIO_PIN_RESET);   //Turn Off LED pin    while (1)  {      HAL_UART_Receive(&huart1, R_Data, 1, 10);  // If button is pressed on the other MCU  if(R_Data[0] == 83)  {  HAL_GPIO_TogglePin(GPIOC, GPIO_PIN_13);                //Toggle LED pin  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);    //Put RS485 module in transmission mode  HAL_UART_Transmit(&huart1, T_Data, 1, 10);             //Send acknowledgment  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  //Put RS485 module in transmission mode  R_Data[0] = 0;  }  // If OK message is receive  if(R_Data[0] == 69)  {  if (HAL_GPIO_ReadPin(GPIOC,GPIO_PIN_13))  {  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  }  else  {  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  }  R_Data[0] = 0;  }  // Button is pressed  if(HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_0))  {  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);    //Put RS485 module in transmission mode  T_Data[0] = 83;  HAL_UART_Transmit(&huart1, T_Data, 1, 10);  T_Data[0] = 69;  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);    //Put RS485 module in Receiving mode  }  }  /* USER CODE END 3 */}Full duplex code#include "main.h" UART_HandleTypeDef huart1; /* USER CODE BEGIN PV */int8_t R_Data[1] = {0};int8_t T_Data[1] = {69};/* USER CODE END PV */ /* Private function prototypes -----------------------------------------------*/void SystemClock_Config(void);static void MX_GPIO_Init(void);static void MX_USART1_UART_Init(void); int main(void){   HAL_Init();   SystemClock_Config();     MX_GPIO_Init();  MX_USART1_UART_Init();  /* USER CODE BEGIN 2 */  HAL_GPIO_WritePin(GPIOC, GPIO_PIN_13, GPIO_PIN_RESET);   //Turn Off LED pin    while (1)  {      HAL_UART_Receive(&huart1, R_Data, 1, 10);  // If button is pressed on the other MCU  if(R_Data[0] == 83)  {  HAL_GPIO_TogglePin(GPIOC, GPIO_PIN_13);                //Toggle LED pin  HAL_UART_Transmit(&huart1, T_Data, 1, 10);             //Send acknowledgment  R_Data[0] = 0;  }  // If OK message is receive  if(R_Data[0] == 69)  {  if (HAL_GPIO_ReadPin(GPIOC,GPIO_PIN_13))  {  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  }  else  {  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  HAL_Delay(500);  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);  }  R_Data[0] = 0;  }  // Button is pressed  if(HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_0))  {  T_Data[0] = 83;  HAL_UART_Transmit(&huart1, T_Data, 1, 10);  T_Data[0] = 69;  }  }  /* USER CODE END 3 */}  

Regarding the design of a micropower isolated power supply for the two-wire transmitter, we must know what is the transmitter first. When the output of the sensor is a specified standard signal, it is called a transmitter. A sensor, usually composed of sensitive elements and conversion elements, is a floorboard for a component or device that can be measured and converted into a usable output signal according to certain rules. And the common types are power transmitters, current-voltage transmitters, and so on.How to Build a FM Radio Transmitter CatalogI. Brief Introduction to Internal Micro-power Supply DesignII. Overall DesignIII. Constant Current Voltage Stabilizing CircuitIV. DC/CD in CircuitV. Isolated Power Source WindingVI. ConclusionFAQ I. Brief Introduction to Internal Micro-power Supply Design The design of an internal micro-power supply is very important when developing a low-power intelligent two-wire transmitter. Firstly, in order to satisfy the power supply of the micro-controller, A/D, D/A, and communication circuit, the intelligent transmitter with microprocessor needs more power than that of an ordinary 4~20mA one), and its power supply efficiency of the internal power supply must be higher.  In addition, for capacitive sensors and thermocouples, it is necessary to consider the case of grounding or the possibility of the sensor earthing. So the input and output of the designed transmitter circuit must be isolated, only this way can guarantee the normal operation of the follow-up control system and the ability of anti-common-mode interference.  Since the external circuit provides the maximum working current of 4mA for the two-wire transmitter system, specific requirements like this bring great difficulties and challenges to the design of the power supply of the system. Adopting a full integrated circuit, the isolated two-wire transmitter power supply with micro-input power has the advantages of simple structure, stable performance, and low cost. And it takes the 12~35V DC as the input power, designing the simple input circuit of the constant current and stable voltage front end, fixing the consumption of 315mA current, and providing two sets of isolated 3V power supply. In this case, the not isolated imputing group with maximum 5mA load capacity and the isolated imputing group with maximum 3mA load capacity, which can meet the requirements of input and output isolating two-wire transmitters for power supply.  II. Overall Design Fig.1 is a schematic diagram of the power supply. It consists of three main parts: 315mA/812V constant current voltage stabilizing circuit composed of U1, R1, and Z1; DC/DC converter circuit composed of U2 as the core; and a set of isolated power supply composed of L2 and U3. The system is designed to be concise and highly integrated, and all selected components can work at -40 ~ 85 ℃, which can ensure the reliable application of the power supply to field transmitters.Fig.1 Schematic Diagram of Power Supply III. Constant Current Voltage Stabilizing Circuit As a power supply to the two-wire transmitter, the maximum working current is 4mA. The transmitter with this power supply needs some low zero output indication, so the general system power supply standard is usually below 315mA, meanwhile, this type of power supply must have constant current characteristics to meet the operating requirements of the two-wire transmitter. And there are many ways to design constant-current sources. The design in Fig.2 adopts the three-terminal adjustable voltage stabilizer LM317L to design a constant-current source. LM317L is a three-terminal adjustable voltage stabilizer, and its application is as follows in Fig.2. Its basic application as a standard regulator is shown in Fig.2 (a), where a steady pressure difference is generated between the output and adjustment terminal, the typical value is 1125V, so its output voltage is VO=1125 (1+Ra/Rb). Because of the stable pressure difference of LM317, it is often used to design the constant-current source. Fig.2 (b) is a typical application circuit, which generates a current of I=1125 / R, consulting Fig.1; the R1 value in the design is 360Ω, so you can obtain a constant current of about 315mA.  Considering the working voltage range of the subsequent DC/DC chip is 4~11V and the actual out the power supply, a voltage stabilizer Z1 with 812V is used to parallel the voltage stabilizing function while providing a stable inlet voltage for U2. It requires that the U2 total current consumption is less than 314mA and Z1 must be the high-quality voltage stabilizer with the breakdown current less than 011mA (Philips products can be used, the lowest static stable current is only dozens of μA). Fig.2 Typical Application of LM317LThe D1 of the front end of the circuit is an anti-inversion diode( as shown in Fig.1), generally using 1N4148. The fuse is the PTC device self-recovery fuse, its parameter is 100mA/ 60V, which ensures that the external power supply will not be affected when the power supply fails. The field transmitter is the final application of the power supply. Its changing ambient temperature is in a wide range, so the temperature drift must be taken into account. The main temperature drift of the power supply is the constant current drift, which is caused by the temperature drift of the reference voltage difference of LM317L and the temperature drift of the constant current resistance R1. In reality, the temperature drift can be neglected when the temperature coefficient is below 5*10-6/℃.  The relationship between the reference pressure difference and temperature coefficient of LM317L is shown in Fig.3: The temperature effect is obvious in the temperature range of - 40-85%, thus compensation must be made in the high precision application. In intelligent transmitter systems, in order to correct sensors and compensate circuits, temperature sensors are commonly designed in the transmitter circuits, because the practical applications of power supply are aimed at intelligent transmitters. But the digital thermometric chip, like LM75 or TC77, does not design a special hardware compensation, while a software compensation algorithm provided when applying power supply to deal with temperature drift.  Fig.3 LM317L Benchmark Temperature CurveAs shown in Fig.3, the curve of the relationship between the reference pressure difference and temperature of LM317L is approximate to a simple cubic polynomial function. It only needs to design a compensation function for the reverse Y-axis, and the system is calibrated at 20 ℃ as the basic compensation. The specific compensation formula is ΔI=A (t-20)2+B (t-20) in which “t” is the ambient temperature. The coefficients A and B can be derived from the reference voltage temperature curve provided by the LM317L chip manual, the simplest method is to obtain two binary linear equation groups for solving A and B by taking two points of -20 ℃ and 60 ℃. In this way, it is easy to obtain an approximate function of the compensation curve with a good fitting degree, and the effect of compensated temperature drift can be neglected basically. The biggest difficulty of power supply design is that the input power is very small, thus the isolated feedback mode with high power consumption should be avoided in the design of the isolation terminal, and the open-loop auxiliary side should be used in the actual circuit. The specific process is using MAX639 to design the core circuit of DC/DC, which realizes the high power efficiency conversion. For example, when the input of 315mA is supplied, it can supply the circuit with a current much larger than that of 315mA, thus solving the need for a large current in an intelligent system. According to the requirements of the system, the core chip must have the advantages of low power consumption, high efficiency, wide input voltage range, and simple peripheral devices. The DC/DC chip in Fig.1 is MAXIM's MAX639, which is a step-down converter chip. Its main features are wide input voltage range (4~115V), high conversion efficiency (up to 90%) and low static current (10 μ A); fixed output or an adjustable output. IV. DC/CD in Circuit The circuit is designed for adjustable output and the output is set to 3V. Output current: Io=（Vi Ii η）/Vo, Vi is the input voltage; Ii is the input current, and η is the conversion efficiency and Vo is the output voltage. In the circuit, Vi=812V, Ii=315mA,η= 90%, Vo=3V, getting an approximation Io=816mA without considering the isolating side output, this output current is already a relatively large supply capacity in the low-power system. But the calculation of the above Io is only theoretical, if you want to make the circuit operate reliably under the condition of micro-input power such as 315mA/812V, and to obtain more than 90% conversion efficiency, it is necessary to design the circuit very carefully. The reliable operation of DC/DC is restricted by many conditions, the necessary condition is providing sufficient start-up pulse current. A 10μF tantalum electrolytic capacitor C2 in parallel to Z1 provides an operation guarantee, also it can effectively avoid the interference of DC/DC work on the constant current of LM317. The inductance L1 plays a decisive role in the conversion efficiency of DC/DC. The algorithm provided by the MAXIM manual is L1=50/I0, μH is the unit of L1 and A is the unit of I0. In the practical circuit, the value of L1 is 4mH, which can ensure the circuit work stably under the maximum output power, and it can keep the high conversion efficiency at the same time. what should be emphasized is that if L1 is small, the conversion efficiency of the circuit will be reduced, the starting current will increase and even can not operate. If L1 is larger, the output capacity will decrease and the DC/DC circuit will oscillate. To ensure the stability of the circuit, DC / DC chip has a high requirement for output capacitor C3, the most important is that its equivalent series resistance ESR must be smaller, and it must have enough capacity at the same time. So a 10μF tantalum electrolytic capacitor with excellent performance is used in the circuit design, which can guarantee a stable output. The DC/DC chip is the core of the circuit, and the actual circuit layout has a great influence on the performance of the circuit, especially on the output ripple. The unreasonable layout design of the circuit board will even bring extra parasitic oscillation in the output, so much more attention should be paid to the design. Thus the most important principle is that the ends of C2 and LI lead should be as close as possible to the MAX639 pin, and the grounding pins of C2, D2, MAX639, R3, and C3 should be as close as possible to each other, linking with thick wires. The setting input voltage of DC/DC is 812V, which is guaranteed by Z1. If the actual transmitter requires a lower power supply, Z1 can choose a lower stable voltage, which makes the whole power supply require a lower input voltage. The low threshold of the inlet voltage is 12V; if Z1 selects 612V, the threshold voltage can be reduced to 10V. V. Isolated Power Source Winding The main feature of the circuit is to provide an isolated power supply winding, which uses the method of "stealing" electricity on the DC/DC output energy storage inductor. In Fig.1, the L2 is the power supply coil for this isolated power supply. Because the isolating power supply is a secondary coil loaded on the energy storage coil of DC/DC, and its structure is an open loop, therefore its output stability is relatively poor. In order to obtain satisfactory results, it is necessary to consider the whole design from different angles.First of all: determine its output power. Because of the method of "stealing" electricity from the energy storage coil, its output power is limited and can only be smaller than the original side output power. The output of this set of isolated power supply is mainly supplied by sensor conversion circuit, front-end A/D converter, and isolated circuit in the application of specific transmitters. And the power consumption of analog measuring circuits of differential capacitance sensors, thermocouple sensors, and thermal resistance sensors reaches μA level. The front-end A/D is usually multi-integral or Σ-Δ, the power consumption is less than 1 mA, and the whole low power dissipation optoelectronic isolation can be below 1mA. Therefore, isolated windings provide 3mA that can meet the actual needs. It has been calculated that the maximum output of the circuit is 816mA without the secondary winding, so it is obvious that the 3mA current can be supplied in the case of the secondary winding. Secondly: Avoid working / hibernating rotation for devices with high power consumption. The isolation winding adopts an open-loop structure, and the change of load on the primary side directly affects the stability of the secondary side, so it is required that the power consumption stability of the original circuit system should be guaranteed as much as possible when the circuit is used in practice. What’s more, the circuit can provide the maximum 5mA current for the original edge and can fully meet the requirements of the commonly used low-power MCU control system without the use of sleep mode. In this way, the maximum system running speed can be obtained. Finally:  the low-voltage difference linear regulator and the DC/DC converter should be used in the design. The isolated power winding mainly supplies power to the front-end small-signal analog circuit, therefore, the quality of the power supply requires high. Noise reduction and voltage stabilization treatment of low voltage output converted by DC/DC through low dropout linear regulator(LDO), which can not only improve the efficiency of power supply but also meet the requirement of small ripple voltage. Specifically, LDO uses MAX1726 chip, its working current is the only 2μA, the output is 313V; The output amplitude before voltage stabilization depends on the output power of the original edge and the inductance of L2, the experiment confirmed that L2 is 3mH. When the primary current varies between 3~5mA and the secondary current is 2mA, the voltage fluctuates between 318V and 418V before the voltage stabilizes, which meets the input requirements of the LDO voltage stabilizer. VI. Conclusion The isolated power supply of two-wire transmitter is stable and reliable, and can meet various complex requirements of the use of two-wire transmitter. It has the characteristics of wide temperature range, wide input voltage range, high output efficiency, high integration, good isolation performance, small volume and low cost. And this power supply has been applied to the integrated intelligent temperature transmitter, after a long period of field test, finding that it has excellent performance and can fulfill the requirements of the isolated two-wire transmitter completely. FAQ 1. What does a transmitter do?In the Telecommunications world, a Transmitter is a device that produces radio waves radiating from an antenna. In the world of process control, a Transmitter is a device that converts the signal produced by a sensor into a standard instrumentation signal representing a process variable being measured and controlled. 2. What is called transmitter?In electronics and telecommunications a transmitter or radio transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. 3. What is transmitter and its types?Pressure transmitters are divided into three types: Absolute Transmitter: This transmitter take vacuum pressure as its base, and then measures process pressure. Gauge Transmitter: This type measures process pressure with the location's atmospheric pressure as a base. 4. What are the main features of transmitter?Some of the main features which make the transmitter complex are higher clock speed, higher transmit power, directional antennas and need for a linear amplifier. 5. What is transmitter frequency?A radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. Radio waves are electromagnetic waves with frequencies between about 30 Hz and 300 GHz. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. 6. What is the difference between transmitter and antenna?A transmitter is a different kind of antenna that does the opposite job to a receiver: it turns electrical signals into radio waves so they can travel sometimes thousands of kilometers around the Earth or even into space and back. Antennas and transmitters are the key to virtually all forms of modern telecommunication. 7. What is difference between transmitter and transducer? Transducers and transmitters are virtually the same thing, the main difference being the kind of electrical signal each sends. A transducer sends a signal in volts (V) or millivolt (mV) and a transmitter sends a signal in milliamps (mA). 8. What is transmitter PLC?Transmitters are also referred to as stationary instruments and convert measurement parameters into an electrical signal that is then sent to a BMS ( Building Management System), PLC ( Programmable Logic Controller), SCADA ( Supervisory Control and Data Acquisition). 9. What is the pressure transmitter?A Pressure Transmitter is an instrument connected to a Pressure Transducer. The output of a Pressure Transmitter is an analog electrical voltage or a current signal representing 0 to 100% of the pressure range sensed by the transducer. 10. Which oscillator is used in transmitter?Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most radio transmitters, and to generate the clock signal in computers and quartz clocks. You May Also LikeThe 3W PowerSpot transmitter for Power Over-the-air from PowercastBuild a Remote RC Firecracker and Firework lgniter Using RF Transmitter4 Channel 2 Core Twisted Pair Remote Controller Using PT2262

SummaryA good news that transmitter industry have a futher development is that powercast,a leader in the field of permanent mold aluminium castings,announced its three-watt PowerSpot transmitter is now FCC-approved and ISED-approved for far field(up to 80 feet) over-the-air charging multiple consumer devices.This kind of transmitter doesn't require charging mats or direct line of sight.Product IntroductionCreating a coverage area like Wi-Fi, a Powercast transmitter automatically charges enabled devices when within range. The RF transmitter uses the 915-MHz ISM band to send RF energy to a tiny Powercast receiver chip embedded in a device, which converts it to direct current (DC) to directly power or recharge that device’s batteries.Powercast is to begin the production of its standalone PowerSpot charger and is also offering a PowerSpot subassembly that consumer goods manufacturers can integrate into their own products. The compay envisions that lamps, appliances, set-top boxes, gaming systems, computer monitors, furniture or vehicle dashboards that are readily wired to an electricity source could all become “PowerSpots” able to charge multiple enabled devices around them.“Consumer electronics manufacturers can now confidently build our FCC-approved technology into their wireless charging ecosystems, and offer their customers convenient far-field charging where devices charge over the air from a power source without needing direct contact, like inductive charging requires, or near direct contact, like magnetic resonance requires,” said Powercast’s COO/CTO Charles Greene, Ph.D. The PowerSpot creates an overnight charging zone of up to 80 feet free of wires or charging mats. Enabled devices charge when in range, but don’t need direct line of sight to the PowerSpot. Powercast expects up to 30 devices left in the zone on a countertop or desktop overnight can charge by morning, sharing the transmitter’s three-watt (EIRP) power output. Charging rates will vary with distance, type and power consumption of a device. Power-hungry, heavily used devices like game controllers, smart watches, fitness bands, hearing aids, ear buds, or headphones charge best up to two feet away; keyboards and mice up to six feet away; TV remotes and smart cards up to 10 feet away; and low-power devices like home automation sensors (window breakage, temperature) up to 80 feet away. An illuminated LED indicates devices are charging and it turns off when they’re done. Audible alerts indicate when devices move in and out of the charge zone. The PowerSpot transmitter uses Direct Sequence Spread Spectrum (DSSS) modulation for power and Amplitude Shift Keying (ASK) modulation for data, and includes an integrated 6dBi directional antenna with a 70-degree beam pattern.  About PowerSpotEstablished in 2003,powerspot is the leading provider of RF-based wireless power technologies that provide power-over-distance,elimiate or reduce the need for batteries,and power or charge devices without wires and connectors.Powercast's IP portfolio includes 45 patents worldwide (21 in the US) and 30 patents pending. 

Before I share it ,I would like to warn that: Fireworks are illegal in many countries. Before you go lighting off fireworks, check for any local restrictions. Stay safe!There are many articles about remote control lgnition system if you google it. However,I would like to share one but it has some differences between them cause the circuit is combined with my ideas and my friend who is an engineer. Let's see the the complete project details that allow you to ignite firecrackers from a safe distance! This circuit comprises three equally important key parts: an electronic igniter,an RF transmitter and RF receiver . Electronic IgniterThe “red-hot” part of the project is an electromagnetic relay controlled heating wire/fuse. The circuit diagram of the electronic igniter shown following is straightforward and self-explanatory. Here, galvanically isolated electromagnetic relay driver circuitry is used to control the heating element/fuse (1.5 in. of 40AWG Nichrome80 wire) from the output of the RF receiver. Because the RF remote control has four independent channels (pins 10–13 of HT12D IC in the receiver), you can replicate this electronic igniter circuitry to build multiple (four) heating lines. However, as 1.5 in. of 40AWG Nichrome wire draws current close to 1.5 A, without a healthy 12-V battery, the electronic igniter probably couldn’t ignite a firework on its output channels.   RF Transmitter and Receiver A transmitter (or radio transmitter) is an electronic device which produces radio waves with the help of an antenna. A transmitter generates a radio frequency current applied to the antenna, which in turn radiates radio waves.There are several different kinds of transmitter ICs. At Future Electronics we stock many of the most common types categorized by data rate, supply current, supply voltage, frequency range, packaging type and output power. Well,An RF module (radio frequency module) is a (usually) small electronic device used to transmit and/or receive radio signals between two devices. In an embedded system it is often desirable to communicate with another device wirelessly. ... RF communications incorporate a transmitter and a receiver. The RF transmitter consists of a 434-MHz license-exempt radio transmitter module and an encoder chip HT12E, while the RF receiver consists of a 434-MHz radio receiver module and a decoder chip HT12D. In case you are facing difficulties in getting this specific item, you can build your own circuitry (on perfboards) by following the open-hardware schematic (shown below) rendered by the eBay seller (B.M. Embedded Solutions, New Delhi, India).     TestAfter I made one,I test it with a  9-V PP3-type battery as the power source of the radio transmitter and a 12-V/2-A lab power supply as the power source for the radio receiver and electronic igniter. With the limited free space there, I didn’t want to risk being responsible for a fire that burned my lab. So I just fired only a couple of homemade fuses as the proof-of-concept. Picture is as following: