Universal stepper motor speed controller
Stepper motor is a digital motor. It rotates as per applied pulses. The pulses have to be applied in specific sequence to motor coil terminals. The speed of motor can be varied by varying the frequency of applied pulses. As the frequency is increased the speed is increased and vice versa. Increasing frequency means decreasing time period – delay of applied pulses. So as the time period of pulses is decreased the speed of motor increases and vice versa. The maximum frequency (means minimum time period) at which the pulses should be applied depends upon the maximum RPM of motor.
The project given here demonstrates how to vary speed of any 6-wire or 5-wire unipolar stepper motor. The given circuit can control speed of any unipolar stepper motor having maximum voltage upto 100 V and current upto 5 A. The circuit uses NPN Darlington transistor TIP122 to drive stepper motor that is capable to handle 100 V @ 5A. The circuit is build using AT89C52 micro controller that varies frequency of applied pulses to vary motor speed from min to max. It also uses LCD to display motor speed from 10% to 100%.
As shown in figure the circuit is built using micro controller AT89C52, LCD and Darlington transistor TIP122.
• Stepper motor is connected to port P2 pins. Port P2 pins P2.0 to P2.3 drives stepper motor through 4 Darlington amplifiers. P2 pins are given to base input of TIP122 and collectors of TIP122 are connected to coil terminals of stepper motor. Two common terminals of stepper motor are shorted and connected to Vcc
• LCD is connected to port P0 and P2 pins. Port P0 drives data pins D0 – D7 of LCD and port P2 pins P2.7, P2.6 and P2.5 are connected to LCD control pins Rs, RW and En pins. One pot is connected to Vee pin as shown to vary brightness of LCD
• A 12 MHz crystal with two 33 pF capacitors is connected to crystal input pins to generate required clock signal