Stepper Motor Control Using the PIC16F684

AN906 Stepper Motor Control Using the PIC16F684 MICROSTEPPING Author: Reston Condit Microchip Technology Inc. Single stepping, or turning a stepping motor at its rated step size, results in less than smooth movement. Microstepping is a technique used to smooth the INTRODUCTION motor's movement between full steps and to improve the step resolution of the motor. Microstepping also This application note describes how to drive a bipolar improves the efficiency of the system, because the stepping motor with the PIC16F684. The Enhanced current in the windings of the motor is manipulated in a Capture Compare PWM (ECCP) module is used to controlled manner rather than being turned on and off implement a microstepping technique known as high- abruptly. torque microstepping. The microcontroller's 8 MHz A microstepping technique known as high torque internal oscillator allows the signals generated by the microstepping alternately varies the current in the two ECCP module to achieve frequencies above the windings of a stepping motor. Figure 1 shows a graph audible range. of the current in the windings vs. angular position using Note: Please refer to AN907: Stepping Motor this technique. Fundamentals for information on the types of stepper motors, microstepping and current limiting techniques. FIGURE 1: HIGH TORQUE MICROSTEPPING nt 1st Winding +3S +6S +9S Curre 2nd Winding Angular Position (S = rated step size) A brief description of what is happening is that one For instance, if a 5V stepping motor is rated at 1 amp, winding is powered while the current in the other wind- then modulating a 5V supply across the winding at 50% ing is gradually dropped to zero, reversed, and then will result in a current of 1/2 amp (assuming a low ramped up again. This sequence is then repeated for inductance motor). Equation 1 shows this relationship: the other winding. Note that the transition between a winding being energized in one direction and then EQUATION 1: energized in the other direction has a sinusoidal shape (refer to Figure 1). This shape gives the smoothest I = D× IMAX