8085 Microprocessor-Based Stepper Motor Control System | Stepper Motor Control Using 8085 Microprocessor
• The motor is controlled by ON/OFF the control winding.
• The popular stepper motor used for demonstration in laboratories has a step size of 1.8° (i.e.,
200 steps per revolution).
• This motor consists of four stator winding and require four switching sequence as shown.
• The basic step size of the motor is called the full step.
• By altering the switching sequence, the motor can be made to run with the incremental motion of half the full-step value. The switching sequence for half-step rotation is shown.
ding stepper motor is shown. The system consists of an 8085 microprocessor as CPU, EPROM, and RAM memory for program & data storage and for the stack.
• Using INTEL 8279, a keyboard and six 7-segment LED displays have been interfaced in the system. Through the keyboard, the operator can issue commands to control the system. The LED display has been provided to display messages to the operator.
• The windings of the stepper motor are connected to the collector of Darlington pair transistors.
• The transistors are switched ON/OFF by the microprocessor through the ports of 8255 and buffer (74LS245).
• A freewheeling diode is connected across each winding for fast switching.
• The flowchart for the operational flow of the stepper motor control system is shown.
• The processor has to output a switching sequence and wait for I to 5 mull-seconds before sending the next switching sequence. (The delay is necessary to allow the motor transients to die- out).
Interfacing Stepper Motor with 8085
Stepper motor is an electromechanical device that rotates through fixed angular steps when digital inputs are applied. It is suitable for precise position, speed and direction control which are required in automation system.
The angle through which stepper motor rotates with a fixed angle for each digital data is called step angle.
Different stepper motor has different step angle. The more frequently used stepper motor has step angle of 0.9 degrees and 1.8 degrees.
Depending on the sequence applied to stepper motor, it can be classified in two category:
1. 4- Step sequence or full step sequence
2. 8- Step sequence or half step sequence
Ex: = 200 steps are required to complete one rotation
Ex: = 50 repetition of sequence = (32) in Hexadecimal.
In this type of functioning, the following 4 binary sequence/code are used for rotation: (Considering step angle= 1.8 degrees)
In this type of functioning, the following 8 binary sequence/code are used for rotation: (Considering step angle= 0.9degrees)
Chips select Logic:
Control word Format:
In the above program in look up table if the 4-step sequence for clock wise then stepper motor will rotate in clockwise direction and if the 4-step sequence for anti-clock wise then stepper motor will rotate in anti-clockwise direction.
Speed control of stepper motor is achieved by writing program to rotate stepper motor continuously in delay program. We can change the delay between two steps and thus change the speed of stepper motor.
Interfacing diagram of Stepper motor with 8085
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