MikroElektronika PIC Microcontrollers PIC18 Instrukcja Użytkownika Pobierz pdf (Strona 55)

Robotics experiment with PIC microcontroller l 55

For Robo-PICA, we prepare the speed control with PWM technique via soft-

ware by the motor.h library file. You can see detail in motor.h sourcecode in Listing 4-1

(in this chapter). motor.h library has PWM function for supporting 2 PWM modules of

PIC16F887 as follows :

Pwm1_Change_Duty(speed); // Motor A Duty

Pwm2_Change_Duty(speed); // Motor B Duty

You can put the required duty cycle value in (speed). The range is 0 to 255 for 0

to 100% duty cycle.

A4.1 Write the Listing A4-1. Compile and download the code to Robo-PICA. Turn-off

power switch.

A4.2 Remove the downlaod cable from Robo-PICA.

A4.3 Place the robot on the floor. Turn-on power to run the program. See the operation.

The Robo-PICA robot will move forward fastest in 2 seconds and spin left

5 second. After that the robot will move foraward with fastest speed again. The robot

will move this routine all times.

Listing A4-1 : The speed control program for Robo-PICA by using PWM.

#include <motor.h>

char i;

void main()

{

Forward(255); // Motor Forward

while(1)

{

Delay_ms(2000);

Pwm1_Change_Duty(220); // Motor A 85% Duty

Pwm2_Change_Duty(255); // Motor B 100% Duty

Delay_ms(5000);

Pwm1_Change_Duty(255); // Motor A 100% Duty

}

The suitable PWM duty cycle value for driving the robot is more than 70%.

If select the less value, the robot has not torque more enough for turning

or rotation.

INNOVATIVE EXPERIMENT

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MikroElektronika PIC Microcontrollers PIC18 Instrukcja Użytkownika Strona 55