Design of stepper motor drive circuit based on single chip microcomputer

AT89C2051 outputs the control pulse from P1.4 to P1.7 of P1 port, and enters 9014 after being inverted by 74LS14. After being amplified by 9014, it controls the photoelectric switch. After photoelectric isolation, the power tube TIP122 amplifies the pulse signal in voltage and current to drive each phase winding of the stepper motor. The stepper motor can perform forward rotation, reverse rotation, acceleration, deceleration and stop according to different pulse signals. In the figure, L1 is a phase winding of the stepper motor. AT89C2051 uses a crystal oscillator with a frequency of 22MHz. The purpose of using a higher crystal oscillator is to minimize the influence of AT89C2051 on the pulse signal cycle of the host computer under mode 2.

In Figure 3, RL1~RL4 are the internal resistance of the winding, and the 50Ω resistor is an external resistor that acts as a current limiter and is also a component that improves the loop time constant. D1~D4 are freewheeling diodes, which attenuate the back electromotive force generated by the motor winding through the freewheeling diodes (D1~D4), thereby protecting the power tube TIP122 from damage.

Connecting a 200μF capacitor in parallel with a 50Ω external resistor can improve the leading edge of the current pulse injected into the stepper motor winding and improve the high-frequency performance of the stepper motor. The 200Ω resistor in series with the freewheeling diode can reduce the discharge time constant of the loop, making the trailing edge of the current pulse in the winding steeper and the current falling time shorter, which also plays a role in improving the high-frequency working performance.

3. Software Design

The driver has three working modes to choose from according to the different combinations of the DIP switches KX and KY:

Mode 1 is the interrupt mode: P3.5 (INT1) is the step pulse input terminal, and P3.7 is the forward and reverse pulse input terminal. The host computer (PC or single-chip microcomputer) is connected to the driver with only two lines.

Mode 2 is serial communication mode: the host computer (PC or single-chip microcomputer) sends the control command to the driver, and the driver completes the relevant control process according to the control command.

Mode 3 is the DIP switch control mode: directly control the stepper motor through different combinations of K1 to K5.

When the power is turned on or the reset button KR is pressed, AT89C2051 first detects the status of the DIP switches KX and KY, and enters different working modes according to the different combinations of KX and KY. The following is the program flow chart and source program of mode 1.

When compiling the program, special attention should be paid to the handling of the stepper motor during commutation. In order to make the stepper motor transition smoothly during commutation and avoid step errors, a flag should be set in each step. The 20H unit is the forward flag of the stepper motor; the 21H unit is the reverse flag. When rotating forward, not only the forward flag is assigned a value, but also the reverse flag is assigned a value; the same is true when reversing. In this way, when the stepper motor commutates, the previous position can be used as the starting point for reverse movement, avoiding step errors when the motor commutates.

Figure 4: Method 1 program flowchart

Method 1 source program:

MOV 20H,#00H; 20H unit is reset to initial value, motor forward position pointer

MOV 21H,#00H; 21H unit is reset to initial value, motor reverse position pointer

MOV P1,#0C0H; Initialize the P1 port to prevent the motor from short circuiting when powered on

MOV TMOD,#60H; Initialize T1 counter and enable interrupt

MOV TL1,#0FFH

MOV TH1,#0FFH

SETB ET1

SETB EA

SETB TR1

SJMP$

;***********Counter 1 interrupt procedure************