Design of stepping motor controller based on single chip microcomputer (forward rotation and reverse rotation indicator gear)

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send out ： Single chip microcomputer stepping motor
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One 、 Design description

1. Design purpose
Through the specific small-scale test system design , Practice the whole process of single chip microcomputer system design and debugging , To deepen the understanding of the internal structure of MCU 、 Understanding of functions and instruction systems , And further learn the application of SCM development system and the interface and programming methods of some peripheral chips , Master the hardware of single chip microcomputer system preliminarily 、 Software design technology and debugging skills .

2. The design requirements
This time I choose to finish the project 1—— Design of stepping motor controller based on MCU .
The design requirements are as follows ：
1） The motor speed can be controlled smoothly ;
2） Set the speed of the motor through the button on the test box or the dial switch , to turn to ;
3） Display the speed trend of the motor ;
4） Complete basic functions ： start-up / stop it , Speed up , Slow down , Positive rotation , reverse ;
5） Use the controls on the experimental box to improve the control effect and control function （ Selected as ）.

3. Instruments and equipment
This experiment is conducted online , Did not go to the laboratory for hardware physical verification , Use only Proteus Software simulation .

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Two 、 Hardware circuit diagram and main chip description

The single chip microcomputer selected for this system is STC89C51. The stepping motor model is 28BYJ48, The motor has four phase windings , The working voltage is +5V, It can share a power supply with the MCU . For four phase winding of stepping motor P1 Oral P1.0~P1.3 control , because P1 Insufficient mouth drive , So use one piece ULN2803 Increase driving power . Use P0 The port is connected with a light emitting diode , Used to display the current status ,P3 Port control motor forward and reverse . According to the system requirements, draw based on STC89C51 The control block diagram of stepping motor controlled by single chip microcomputer 2.1 Shown .
The system mainly includes single chip microcomputer 、 Reset circuit 、 Crystal oscillator circuit 、 Key circuit 、 Digital display circuit 、 Stepping motor and driving circuit .

1. Minimum system circuit of single chip microcomputer
The minimum system of single chip microcomputer is the most basic and main part of the application of single chip microcomputer expansion development , It is generally composed of the following circuits , It is the core of the whole design, which ensures the expansion and Realization of other functions based on MCU . Pictured 2.2 Shown .

Reset circuit : Reset circuit is the most basic and important circuit in the application of single chip microcomputer , It is used to deal with urgent problems such as single chip microcomputer failure . When the reset port of MCU is at high level , The code in the MCU will not be executed . At the beginning of power on , The capacitor is not fully charged , Reset the port to high level , It avoids program errors caused by running the program directly after power on . When the capacitor is fully charged , The reset port becomes low , The program starts running .

Crystal oscillator circuit : Crystal oscillator circuit is also a necessary circuit in the design of MCU , Provide working sequence for the system . Crystal oscillator circuit provides 11.0592MHZ clock frequency , So as to form the whole stable oscillation circuit , Provide guarantee for the normal operation of single chip microcomputer .

2. Digital display circuit
The nixie tube shows the electrical route 1 position 7 paragraph LED The nixie tube displays the current speed and gear （ common 9 A gear ）, See the picture for details 2.3 Shown .

3. Key circuit
The key circuit needs to realize the key to control the forward rotation of the stepping motor 、 reverse 、 Speed up 、 Slow down 、 stop it , All in all 5 A button , See the picture for details 2.4 Shown .

4. Motor and drive circuit
Electric motor and drive circuit ULN2003 Driver chip 、DC-5V Stepper motor 、 Revolution indicator light, etc , See the picture for details 2.5 Shown .

5. The overall circuit of the system

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3、 ... and 、 How the system works

1. Minimum control system
Pictured 3.1, This design uses STC89C51 Single chip microcomputer , This type of single chip microcomputer is STC A low power consumption produced by the company 、 High performance CMOS8 Bit microcontroller , have 4K In system programmable Flash Memory .. On a single chip , Have dexterous 8 position CPU And in system programmability Flash, It can completely meet the needs of this design . Yes STC89C51 Single chip microcomputer , The minimum control system should generally include ： Reset circuit 、 Clock circuit .

Reset circuit ： The reset circuit adopts manual reset , The so-called manual reset , It refers to turning on the button switch , Make the single chip microcomputer enter the reset state .

Clock circuit ： use 22pF Capacitance and 12MHz The crystal oscillator provides the clock frequency for the whole circuit . The clock signal of single chip microcomputer is usually obtained by two circuit forms ： Internal oscillation mode and external interruption mode . At pin XTAL1 and XTAL2 External crystal oscillator circuit （ Crystal oscillator for short ） Or ceramic crystal oscillator , It forms the internal crystal mode . Because there is a high gain inverting amplifier inside the MCU , After the external crystal oscillator , It forms a self-excited oscillator and generates an oscillating clock pulse . The capacitance of the external circuit with internal oscillation mode is generally 5~30 pF, The typical value of crystal oscillator frequency is 12MHz, use 6MHz There are more cases .

2. Drive circuit
ULN2803 High voltage and High Current Darlington transistor array , In this array 8 Ludlington transistor is a low logic level digital circuit （TTL、COMS、PMOS or NMOS） With high voltage and high current equipment （ Such as relay 、 Machine hammer 、 Light bulb: ） Ideal device for interface .ULN2803 The internal structure and external pins of the driver are shown in the figure 3.2 Shown .1-8 The foot is the input ,9 Foot joint GND,10 Pin connected load power supply +,11-18 Pin connected output . The left side of the figure below is the input （ Assuming that 1 foot ）, The upper right corner is the output （ Corresponding 18 foot ）,pin10 by 10 Pin connected load power supply +. When 1 Foot joint +5V When the triode is saturated , here 18 Foot output , The second triode from left to right turns on , Connect the load power GND, At this time, the load is powered on .

Darlington tube is also called composite tube . It is a common base combined amplifier , To form an equivalent new triode . This is equivalent to the amplification factor of the triode is the product of the two . In electronic circuit design , Darlington connection is often used in power amplifiers and regulated power supplies .
Darlington tube is a compound triode , He connected two triodes in series , The emitter of the first tube is connected to 2 The base of a tube , Therefore, the magnification of Darlington tube is the product of the magnification of two triodes . So it is characterized by very high magnification , The function of Darlington tube is generally to amplify very small signals in highly sensitive amplification circuits , Such as high-power switching circuit .

3. Stepper motor
Because the stepping angle of the stepping motor in this design is 18°, Stepping motor assembly Step Angle The default value of the property is 18, In the mode of four phases and eight beats , The step angle of each shot is 9°, Every output 8 Excitation sequence array of bytes FFW when , The motor steps in total 72°, so , Drive the motor for one revolution （360°） A common need 5 Row excitation sequence array FFW, Make the motor rotate n Circle needs to output 5n Row excitation sequence array FFW. The reverse rotation control principle of stepping motor is the same as that at this time .
Based on the above analysis , Can be designed separately STEP_MOTOR_FFW And STEP_MOTOR_REV function , They are respectively used to control the forward and reverse rotation of the stepping motor n circle , Its internal circulation is 8 Time , The external circulation is 5n Time .
choose ULN2803 As a driver chip , Through MCU P1.0_{P1.3 Output pulse to chip 1B}4B mouth , After amplification, from 1C~4C The ports are respectively output to the A、B、C、D phase , Pictured 3.3 Shown .

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Four 、 Programming

According to the design requirements , The following specific functions need to be realized through software programming ：
1） Drive each module to work , Realize the clear display of digital tube , Realize motor drive ;
2） Realize the forward rotation of the stepping motor controlled by the key 、 reverse 、 Speed up 、 Slow down 、 stop it ;
3）2 LEDs show positive and negative ,1 position 7 paragraph LED The nixie tube displays the current speed and gear ;
4）4 A red LED, Indicates the speed of the motor .

( The following is omitted , See the original report for details )