1,、 Clear development direction and functional planning
The primary task before developing a human scale PCBA solution is to determine the product * and functional requirements. This requires a thorough consideration of the characteristics of the target market and user group. If targeting fitness enthusiasts, in addition to basic weight measurement functions, the product also needs to add measurement functions for body indicators such as body fat percentage, muscle mass, and moisture content, and support connection with fitness apps for users to record and analyze data; For daily household use, ease of operation and measurement accuracy are key, and multi-user modes can also be set to meet the different needs of family members. Here are some common functions:
Basic weighing function: It can quickly and accurately measure weight, with high-precision sensors and processing capabilities to ensure the reliability of measurement data. For example, the common human scale has a division value of up to 0.1kg, which meets the basic requirements of users for accuracy.
Unit switching function: supports multiple unit displays such as kilograms (kg), pounds (lb), ounces (oz), etc., making it convenient for different users' usage habits.
Data recording and storage: It can store historical measurement data of multiple users, making it easy for users to track their weight change trends. Some high-end products can even store measurement data for several years.
Wireless connection function: With the help of wireless communication technologies such as Bluetooth and Wi Fi, measurement data can be synchronized to mobile apps or cloud platforms to achieve remote management and analysis of data.
2,、 Analysis of Working Principle
The human scale mainly works based on the principle of gravity measurement, and different types of human scales have slight differences in specific implementation methods.
Principle of strain measurement method: Taking the common electronic body scale as an example, the strain gauge is attached to the elastic body of the weighing sensor to form a Wheatstone bridge. When there is no load, the bridge is in a balanced state and the output is zero. When the elastic body is subjected to a load, each strain gauge will generate strain proportional to the load and release a certain strain voltage inside the chip. Next, the amplified voltage signal is converted into a digital signal by the analog-to-digital conversion module, and finally sent to the microcontroller for processing and display, thereby achieving weight measurement. Weighing sensors usually attach strain gauges to aluminum rods and consist of bridge resistors to form strain gauges. When the aluminum rod deforms under stress, the four resistors on the strain gauges will produce strain coefficients.
Principle of bioelectrical impedance analysis: The intelligent body fat scale uses bioelectrical impedance analysis (BIA) to measure body fat. The principle is to achieve measurement by sending a low and safe current to the body. Due to the fact that current can freely pass through the fluid in muscle tissue, but encounters resistance when passing through adipose tissue, known as bioelectrical impedance. The body fat scale generally adopts the BIA method with 4 electrodes, which sends a 50kHz excitation signal around the foot through 2 electrodes, and then detects the voltage signal from the other 2 electrodes. After amplifying, rectifying, A/D converting, and MCU processing the voltage signal, the human impedance can be obtained. Combined with the human body model, measurement data such as human fat can be obtained.
3、 Hardware Design
Selection of core components
Main control chip: As the core of the human scale, the main control chip is responsible for data processing, computation, and communication with other modules. You can choose a microcontroller specifically designed for electronic scales, such as SIC8833. It is an 8-bit RISC MCU with a 24 bit ADC, built-in 8K x 16 bit OTP program memory, and has 24 bit bidirectional I/O ports. It is widely used in electronic scales and precision measurement and control systems. In addition, some main control chips that integrate high-precision ADCs, LCD/LED driver chips, and communication chips can effectively reduce the number of peripheral devices and overall machine costs.
Weighing sensor: The performance of the weighing sensor directly affects the measurement accuracy and stability of the human scale. Common types include resistance strain sensors, which have the advantages of high accuracy, good stability, and low cost. When selecting sensors, it is necessary to make a reasonable selection based on factors such as the range and accuracy requirements of the human scale. For example, a human scale with a range of 150kg can use sensors of corresponding specifications to ensure measurement accuracy.
Power management chip: responsible for managing the power supply of the human scale, realizing functions such as battery charging and discharging management, voltage conversion, etc., to reduce power consumption and extend battery life. If a low-power power management chip is used, the current of the human scale in standby mode can be reduced to an extremely low level.
Wireless communication module: If the human scale supports wireless connection functions such as Bluetooth and Wi Fi, the corresponding wireless communication module needs to be selected. For example, the Bluetooth module can achieve short-range wireless communication with devices such as mobile phones, making it convenient for users to synchronize data.
Circuit Design
Measurement circuit: mainly composed of weighing sensors and related signal conditioning circuits, responsible for amplifying, filtering and processing the weak electrical signals output by the sensors to meet the requirements of subsequent analog-to-digital conversion.
Analog to digital conversion circuit: converts analog signals into digital signals for processing by the main control chip. High precision analog-to-digital converters can be used to ensure the accuracy of data conversion.
Display circuit: used to drive the display screen and visually display measurement data to the user. Common display screens include LCD and LED. It is necessary to choose the appropriate display mode according to product requirements and design the corresponding driving circuit.
Power circuit: provides stable power supply for the entire system, including battery power supply circuit, charging circuit, etc. At the same time, the stability and anti-interference ability of the power supply should be considered to ensure the normal operation of the system.
4,、 Software Design
Bottom layer driver development: Write driver programs between the main control chip and various hardware modules to achieve hardware control and data acquisition. For example, writing a driver program for a weighing sensor to obtain measurement data output by the sensor; Write a driver program for the wireless communication module to achieve communication with external devices.
Algorithm design: Develop algorithms for data processing and analysis, such as weight measurement algorithms, body fat percentage calculation algorithms, etc. These algorithms need to be designed based on the working principle and functional requirements of the human scale to ensure the accuracy and reliability of the data.
User interface design: Design a user-friendly interface to facilitate user operation of the human scale. The user interface can include menu interfaces on the display screen, operation prompts, and interface design for mobile apps. The interface of the mobile app should be simple and intuitive, making it easy for users to view and manage measurement data.
Data storage and management: Implement local storage and remote synchronization of measurement data. Remote synchronization involves uploading data to cloud platforms or mobile apps through wireless communication modules to achieve data backup and sharing.
5、 Testing and Optimization
Functional testing: Conduct comprehensive testing of various functions of the human scale to ensure that it meets design requirements. For example, to test the accuracy of the weighing function, standard weights can be used for calibration to check whether the error between the measured data and the standard value is within the allowable range; Test the wireless connection function and check if it can communicate normally with mobile apps or other devices.
Performance testing: Testing the performance indicators of the human scale, such as power consumption, stability, response time, etc. By optimizing hardware design and software algorithms, power consumption is reduced, and the stability and response speed of the human scale are improved.
Reliability testing: Conduct reliability tests such as drop tests, high temperature and humidity tests, etc., to ensure that the human scale can still function normally in various harsh environments. Based on the test results, improve and optimize the product to enhance its reliability and durability.
6,、 Production and Quality Control
After completing development and testing, enter the production phase. In the production process, strict quality control is necessary to ensure that every product meets the design requirements.
PCBA processing: Choose a professional PCBA processing manufacturer to ensure the quality and soldering process of the circuit board. During the PCBA processing, strict quality inspections must be carried out, such as visual inspection, welding quality inspection, etc., to promptly identify and solve problems.
Assembly and testing: Assemble the PCBA board with other components to complete the overall assembly of the human scale. During the assembly process, attention should be paid to the installation position and connection method of each component to ensure assembly quality. After assembly, conduct a complete machine test to recheck the product's functionality and performance, ensuring that the product quality is qualified.
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