Stepper Motor Interface
The complete board consists of transformer, control circuit, keypad and stepper motor as shown in snap.
The circuit has inbuilt 5 V power supply so when it is connected with transformer it will give the supply to circuit and motor both. The 8 Key keypad is connected with circuit through which user can give the command to control stepper motor. The control circuit includes micro controller 89C51, indicating LEDs, and current driver chip ULN2003A. One can program the controller to control the operation of stepper motor. He can give different commands through keypad like, run clockwise, run anticlockwise, increase/decrease RPM, increase/decrease revolutions, stop motor, change the mode, etc. Unipolar stepper motor:-unipolar stepper motor has four coils. One end of each coil is tied together and it gives common terminal which is always connected with positive terminal of supply. The other ends of each coil are given for interface. Specific color code may also be given. Like in my motor orange is first coil (L1), brown is second (L2), yellow is third (L3), black is fourth (L4) and red for common terminal.
By means of controlling a stepper motor operation we can
1. Increase or decrease the RPM (speed) of it
2. Increase or decrease number of revolutions of it
3. Change its direction means rotate it clockwise or anticlockwise
To vary the RPM of motor we have to vary the PRF (Pulse Repetition Frequency). Number of applied pulses will vary number of rotations and last to change direction we have to change pulse sequence.
So all these three things just depends on applied pulses. Now there are three different modes to rotate this motor
1. Single coil excitation
2. Double coil excitation
3. Half step excitation
The table given below will give you the complete idea that how to give pulses in each mode
Table 5.7 Pulses for stepper motor module
The circuit consists of very few components. The major components are 7805, 89C51 and ULN2003A.
1. The transformer terminals are given to bridge rectifier to generate rectified DC.
2. It is filtered and given to regulator IC 7805 to generate 5 V pure DC. LED indicates supply is ON.
3. All the push button micro switches J1 to J8 are connected with port P1 as shown to form serial keyboard.
4. 12 MHz crystal is connected to oscillator terminals of 89C51 with two biasing capacitors.
5. All the LEDs are connected to port P0 as shown
6. Port P2 drives stepper motor through current driver chip ULN2003A.
7. The common terminal of motor is connected to Vcc and rest all four terminals are connected to port P2 pins in sequence through ULN chip.