Stepless speed regulation of DC motor
Hardware design and implementation
2.1 Basic scheme of hardware design
According to the design requirements of a DC motor speed control device based on AT89C2051 single-chip microcomputer, the PWM pulse width signal output is generated by using AT89C2051 single-chip microcomputer as the core. The peripheral circuits are power supply circuit, keyboard and motor drive circuit.
2.2 Power supply part
Power supply part through 220V-7.5V transformer transformer isolation, rectifier bridge rectification, filter capacitor filter, three-terminal regulator IC 78M05 regulator output 5V voltage for the entire device
2.3 motor drive part
The PWM pulse width signal is output by the AT89C2051 single-chip microcomputer, but since the DC output current of the single-chip microcomputer is 25mA [3], it cannot be directly used to drive a small DC motor, and the pulse width signal of the output must be power amplified. The P3.2 port pulse width signal of the single chip microcomputer is sent to the TIP127 power tube through R1 to complete the power amplification, and the amplified signal can drive the DC motor to make it work. The capacitor C1 is a filter capacitor, which can make the voltage of the input DC motor tend to be smooth, and also has the freewheeling effect after the triode is turned off.
3, software design and implementation
A program flow chart of a DC motor speed control device based on AT89C2051 is shown in Fig. 4. Initialize after booting; output PWM signal with duty cycle 0 after initialization; then execute the keyboard scan program, the microcontroller will start scanning the keyboard.
4 Conclusion
The system uses AT89C2051 single-chip microcomputer as the control core, adopts the PWM pulse width modulation method, and uses the medium power tube TIP127 to power-amplify the output PWM signal to drive the 6V, 0.3W micro DC motor. In the design of the device, the hardware circuit is simple, and the open-loop control of the DC motor speed is realized with fewer components. The method described in this paper has been applied to the DC motor speed control system of light load, and the system is stable and reliable.
