This PC-based stepper motor controller is probably the smallest, least expensive, and easiest to use. A bipolar stepper motor with a step resolution of 18 degrees per pulse is controlled by a pair of H-bridges and a software program written in "C++." The PC-based stepper motor controller consists of both a driver circuit and a switching circuit. The stepper motor is driven by a circuit called the "driver," and the switching circuit decides how the motor is driven. So, the switching circuit is the main thing that controls the motor. The switches are the transistors (T1 through T8). Through the data pins D0 through D7, the software controls how these transistors turn on and off. You can change the speed, the direction, and the number of steps of a stepper motor. To change the speed of the motor, you have to change how often the pulses come out (PRF). To change the direction of the motor, you have to change the order of the pulses that are sent to its coils. By limiting

the number of pulses that are sent to the motor, you can make it move only the number of steps you want.

Fig. 1: Circuit of PC based stepper motor controller Details about the stepper motor Stepper motors with different ratings and specifications can be bought on the market and used for different tasks. Here, the 8.9cm (3.5-inch) floppy drive stepper motor is used. It is a bipolar stepper motor with a 5V DC rating and an 18o per pulse step resolution. The motor has two coils on the inside and four terminals on the outside, which are sometimes color-coded. Stepper motors with different step sizes (like 1.8o per pulse) can also be used with this circuit and control software. These motors should be rated for 5V and up to 1A of current.

H-Bridge driver: H-Bridge is a common, well-known circuit that is often used to drive a stepper motor. There are four transistors connected in a bridge (see Fig. 1). The bipolar stepper motor has two coils, so it uses two H-bridge circuits, one for each coil. The transistors T1 through T4 make up

one H-bridge, and the transistors T5 through T8 make up the other bridge. The BD139 type transistors T1 through T8 should be used with heat sinks. Figure 2 shows the pins of BD139 and the regulator IC 7805. Through current-limiting resistors R1 through R8, the bases of all eight transistors are connected to the data pins (D0 through D7) of the 25-pin, D-type male connector. Fig. 3: Power supply for the circuit Through resistors R1 and R2, the bases of transistors T1 and T4 are connected to parallel-port pins 2 (D0) and 3, and the bases of transistors T2 and T3 are connected to parallel-port pins 4 (D2) and 5, respectively. As shown in Fig. 1, the red and orange ends of the first coil (COIL1) are connected to the first H-bridge. Resistors R5 and R6 connect the bases of transistors T5 and T8 to pins 6 (D4) and 7 (D5), respectively. Resistors R7 and R8 connect the bases of transistors T6 and T7 to pins 8 (D6) and 9 (D7), respectively. As shown in Fig. 1, the yellow and green ends of the second coil (COIL2) are connected to the second H-bridge. Getting power Fig. 3 shows the part that has to do with the power supply. It has a 230V AC to 9V AC, 1A secondary transformer (X1), a filter, bridge rectifiers, and a 5V DC regulator (7805). (IC1). The H-bridge circuits are linked to the 5V

DC that has been regulated. The ground of the circuit is shorted to pins 18 through 25 of the D-type parallel-port connector. When the switch S1 is shut, LED1 lights up to show that there is power in the circuit. Operation To make the motor turn either clockwise or counterclockwise, a specific sequence of pulses is sent to the red and orange terminals of COIL1 and the yellow and green terminals of COIL2. This is explained in the next paragraph. Direction control In Tables I and II, a "0" means that the logic is low and a "1" means that the logic is high. We know that the direction of the current is from high to low. To change the direction of rotation, all you have to do is change the way the current flows through the coils. Handle speed To change the speed, you have to change the number of times a pulse is sent out (PRF). With a PRF of 20 Hz, the stepper motor will get 20 pulses in one second. Since the motor's step resolution is 18o/pulse, it will turn 20 times 180o, which is 3600, or one full turn, in one second. So the motor turns once every second, or 60 times per minute. Now, if you double the PRF from 20 Hz to 40 Hz, the RPS will also double to 2 RPS (120 RPM).