Weighing control system provides more convenience in daily life, can play an important role in reducing the work intensity and perfecting the working environment, and has become an important means of weighing and transportation for human beings. At present, most weighing control systems use relay or programmable controller (PLC) control method, which has the disadvantages of high cost and three-phase power.

In this paper, a microcontroller-based weighing control system design is investigated. The microcontroller as the core, and then supplemented with appropriate hardware circuits and control programs to detect and control the signal of the whole weighing, which has the advantage of low cost, versatility, flexibility, easy to expand and easy to perform complex control, the main focus on the basic theoretical knowledge combined with the actual situation, and at the same time on their own independent innovation and analysis of the problem of the ability to cultivate, deepen the understanding of the knowledge, for future research Lay a solid foundation for future research. This paper introduces the overall design of the research background and key technologies, and puts forward the significance of the new weighing control.

2 Composition of weighing control system

The overall part of the weighing control system is divided into three main parts, data acquisition module, controller module and human-machine interface module. The data acquisition module is composed of signal processing and A/D conversion. The converted digital signal is immediately transmitted to the microcontroller for processing, and the microcontroller carries out further processing of the digital quantity, and then drives the weighing module, the display circuit module and the alarm module to complete the exchange of information between man and machine as well as to realize the function of alarm prompting.

The weighing control system adopts HX711 module for weight detection; adopts 5V four-phase stepping motor to deliver the weighed items to the designated position, and is equipped with status indicator to facilitate the display of the position and the operation of the weighing system; and installs the peak buzzer to provide the arrival position and the safety prompts. The position information and the pressure limit can be adjusted by pressing the keys, the OLED displays the current pressure, the pressure limit and the position, the LEDs indicate the direction of operation of the weighing system, the buzzer indicates the position reached at each position, the buzzer indicates when the weight exceeds the limit of the weighing module and the weighing system stops running, the upper unit displays the pressure value in real time.

2.1 Introduction of the weighing system modules

2.1.1 Introduction of A/D converter

A/D converter is a kind of input analog voltage, analog current can be converted into digital quantity which is proportional to it, that is to say, it can be the analog quantity to carry on the specific some processing to convert into the specific digital signal.A/D converter has more varieties, from the principle can be divided into four kinds: double integral A/D converter, successive approximation A/D converter, parallel A/D converter, counter A/D converter and A one Z type A/D converter. and A-Z type A/D converter. In the design of the weighing control system, the more used is the double integral type A/D converter and A a three type A/D converter.

Double area-integrated digital-analog converter has a very strong anti-interference ability. The positive and negative symmetry can make the industrial frequency interference signal simplified to zero, so the 50Hz industrial frequency interference suppression ability is relatively good. In the industrial frequency interference also has a very good filtering effect. If the average value of the interference voltage is zero, there will be no effect on the output. Especially for this system, the gradual change of the pressure signal, will soon be interfered with by the industrial frequency signal, so the application of double integral type digital-to-analog converter can largely reduce the requirements of the filtering circuit.

For the weighing system, HX711 is a good choice. HX711 is a 24-bit A/D converter chip designed for high-precision load cells; compared with other chips of the same type, it integrates the peripheral circuits required for other types of chips, including an on-chip clock oscillator and a regulated power supply. It has the advantages of fast response, high integration and strong anti-interference; the interface and programming of the back-end MCU chip and the chip are easy, all control signals are driven by the pins and there is no need to program the chip's internal register P. The input selector switch and can be used to select channel A or channel B to connect to its internal low-noise programmable amplifier. Channel A has a programmable gain of 128 or 64, corresponding to a full-scale differential input signal amplitude of 20 mV or 40 mV, respectively, while channel B has a fixed 64 gain and is used to detect system parameters. Regulated power supply within the chip can be directly to the external sensors chip within the A/D converter and external sensors to supply power, the system board does not require other analog power supply chip on the clock oscillator does not require other external components. The automatic reset function at power-on simplifies the reset function at power-on.

Generally in use, HX711 mainly converts the analog signal generated by the weighing module into a high-precision digital signal for microcontroller processing. Among them: GND means ground; DT functions as serial data output, SCK functions as power-off control and serial clock input, and VCC means connecting to 5V.

2.1.2 Selection of Microcontroller

Serial converter is Italy's GSMicroelectronics and France's ThomsonSemiconductor merged STMicroelectronics developed, ARMCortex-M core 32-bit microcontrollers are designed specifically for its embedded applications. Its advantage is the low cost of smaller power consumption, but good performance, which serial converter F103C8T6 is a better choice.

Serial converter F103C8T6 microcontroller is the core of the entire weighing system controller system, from which the other modules for the instruction of the command and the integration of resources, to achieve the corresponding functions, reduce unnecessary wiring. The microprocessor has high performance, low power consumption, maximum integration and integration, easy to develop, programmable memory within the system and the existence of cost-effective, strong anti-interference ability. In addition, it has a lot of peripheral function modules, according to the program routines provided by the manufacturer, instructions for use and the corresponding debugging assistant software, etc., can be quickly programmed. It is a kind of special effect function with compatible MCS51 microcontroller, operating voltage 3.5V~5.5V, full static clock OHz~33MHz, three-level program encryption, 32 programmable I0 serial ports, 6/8 interrupt sources, 2/3 16-bit timer/counters, full-duplex serial communication ports, and supports Idle and Power-down modes at lower power consumption. Powerdown mode supports wake-up interrupt, watchdog timer, double data pointer, power-on reset flag. In addition to the external expansion of 32K data memory to meet the system requirements B

2.1.3 Stepping Motor Driver Module

The rotation of the motor is to transform the pulse electrical signal into the corresponding angular displacement or linear displacement, is to give a pulse signal. The angular displacement of the motor is proportional to the number of pulses, and its rotational speed is proportional to the pulse frequency (f). In the case of non-overloading, the rotational speed of the motor and the stopping position depend only on the frequency of the pulse signal and the number of pulses and are not affected by the load change, i.e., if a pulse signal is given to the motor, the motor rotates through a step angle. Due to the microcontroller drive current is small, can not be used directly to drive the motor, the advantage can not be fully demonstrated, so generally use the Darlington array drive can provide a larger torque for the motor, so that the motor works stably In this paper, the choice of 5V four-phase stepping motor can be directly connected to the chip ULN2003, through the microcontroller I / O pin state of the change in the chip and then change the level of the control side, it allows the control of the ULN2003 is a high-voltage performance, consisting of seven silicon NPN Darlington tube, can directly drive relays and other load chips.

2.1.4 Alarm Module

To take into account the safety issue, when the loaded weight is greater than the set pressure value, it means that the system has been overweight at this time, in order to user safety, at this time can not be allowed to run the weighing system, this time you need to start the buzzer alarm system, prompting the user at this time has been overweight, when the load cell monitors the pressure in the operation of the permissible range, the user can choose the position they need to reach according to their needs this design utilizes the This design utilizes a 5V four-phase stepper motor to design the transmission system, the stepper motor is turned upward to transmit, the stepper motor is reversed downward to transmit, when it reaches the specified position selected by the user with the key, the motor stops running, at this time, the buzzer prompts to arrive at the selected position, and the OLED display will also show the position arrived at, the LED light can real-time display of the direction of the transmission operation.

2.1.5 Output Display

The working principle of LCD display: the main material of liquid crystal display is liquid crystal. It has the fluidity of liquid in a specific temperature range, but also has some optical properties of crystal, its transparency and color with the electric field, magnetic field, illumination and other changes in external conditions and changes. Therefore, with liquid crystal made of display devices, you can reflect the changes in the external conditions mentioned above to form the effect of reality. Although ZLG7289 has the function of controlling the display of digital tubes, but considering the Chinese display, consider using the LCD with Chinese character libraries. As it can be displayed in pages, without too large a screen, the final choice of dot-matrix 128x64 type LCD-OCM4x8c.

3 weighing system software and hardware program analysis

3.1 Hardware program

Weighing control system design is mainly to achieve the function of using stepper motors to control the operation of the weighing system; adjust the position by pressing the key, OLED screen displays the current pressure, pressure amount and position, LED lights indicate the direction of the direction of the maximum load limit, more than the weight of the buzzer to start the alarm prompts, and to stop the operation; arrive at the location selected by the key, buzzer prompts to arrive.

The system starts initialization, the weighing module gets the current pressure value. The destination position, the current position, the data acquired by the load cell and the pressure limit are displayed on the OLED display. According to the program written, the system determines whether the current location is the same as the selected location, if not, the system runs so that it reaches the selected location. This design uses a separate power supply system to power the microcontroller, HX711 circuit and sensors.

3.2 Software Program

The weighing system instrument software consists of two main parts: the main program and the interrupt service program. The software design uses the display part, the stepper motor drive part, the weighing module part, the control system part, the alarm part, and the transmission data part.

4 Conclusion

This paper is based on the serial converter weighing control system. Serial converter is a microcontroller, which has more advantages compared to PLC, programmed on KEL and burned into the microcontroller. This design achieves the following functions: stepper motor to realize the control function; can adjust the position of the transmission and the pressure limit by pressing the key; OLED screen displays the real-time arrival position, the pressure limit amount and the real-time pressure: LED lights indicate the up and down direction; when the weight exceeds the limit of the metering module, the buzzer will sound an alarm and it will stop the operation; when it reaches the destination position, the buzzer sounds to indicate that the specified position has been reached; The upper computer VB can read the pressure data in real time, with the limit amount. This paper completes the hardware and software design, circuit welding, system debugging and other work. After testing, the system basically meets the design objectives. Solved the weighing control system in the design of the optimization problem, to determine the chemical, precision design ideas.