RPI Drive servo by PWM (wiringpi / C programming)

Question

I trie to drive a servo with the Raspberry PI using the PWM on GPIO Pin 18 i wired the setup like you can see below.

When i drive the servo i can do this without any problems the commands that i use you can see below.

     gpio -g mode 18 pwm
     gpio pwm-ms
     gpio pwmc 192
     gpio pwmr 2000
     gpio -g pwm 18 150
     gpio -g pwm 18 200

That works fine, to go to the position without any problem but when i try to do the same with a C program using wiringpi like you can see below.

#include <wiringPi.h>
#include <stdio.h>

int main (void)
{
   printf ("Raspberry Pi wiringPi test program\n");
   wiringPiSetupGpio();
   pinMode (18, PWM_OUTPUT) ;
   pwmSetMode (PWM_MODE_MS);
   pwmSetRange (2000);
   pwmSetClock (192);
   pwmWrite(18,150);
   delay(1000);
   pwmWrite(18,200);
   return 0;
}

The program and the raspberry pi chrash so i have to reboot them does anybody know what i do wrong and how i can solve the problem it is very frustrating?

Answer 1

I spent weeks on controlling two servo (SG90) using WiringPi and programming in C, there're three things that I recommend.

1.Using BCM GPIO instead of WiringPi Pin because controlling more than one servo, you might need more than one pin such like 1( WiringPi Pin )/18( BCM GPIO ) for another servo, For RPi3 B+ version, it give access to two channels for hardware PWM. Channel 0 on gpios 12/18 and channel 1 on gpios 13/19, it's easy and no need to worry about pin mapping exists if you adpopt BCM GPIO .

2.Better make sure there is only one program access PWM. pins at one time. Based on my experience, if you find that using command like " gpio -g pwm 18 25 " is workable but otherwise using code like " pwmWrite(18, 25) " doesn's get any servo responds, maybe try " ps -A " to make sure if any other program is racing the access of your servo.

3.The last and the hardest one for me, when I execute pwmWrite(18, 25) " on PWM. pin 18 triggers the same instruction onto PWM. pin 12 , which means pwmWrite(18, 25) triggers pwmWrite(12, 25) . To solve this situation, changing the modes of other pins of servos which should freeze without any moving to be input mode and set all of them to be pull-down.

For details, codes for controlling two servos with PWM. Channel 0 on gpios 12/18.

Basic function:

void servo_init() {
    servo_open(0);
    delay(DELAY_SERVO);
    servo_open(1);}

and

void servo_open(int servo) {
switch (servo) {
    case 0:
        pullUpDnControl(SERVO_0, PUD_OFF);
        pinMode(SERVO_0, PWM_OUTPUT);
        pwmSetMode(PWM_MODE_MS);
        pwmSetClock(PWM_CHANNEL_0_CLOCK);
        pwmSetRange(PWM_CHANNEL_0_RANGE);
        break;
    case 1:
        pullUpDnControl(SERVO_1, PUD_OFF);
        pinMode(SERVO_1, PWM_OUTPUT);
        pwmSetMode(PWM_MODE_MS);
        pwmSetClock(PWM_CHANNEL_0_CLOCK);
        pwmSetRange(PWM_CHANNEL_0_RANGE);
        break;  
    default:

        break;
}}

and

void servo_close(int servo) {

switch (servo) {
    case 0:
        pinMode(SERVO_0, INPUT);
        pullUpDnControl(SERVO_0, PUD_DOWN);
        break;
    case 1:
        pinMode(SERVO_1, INPUT);
        pullUpDnControl(SERVO_1, PUD_DOWN);
        break;  
    default:

        break;
}}

and

void servo(int servo, int angle) {
switch (servo) {
    case 0:
        servo = SERVO_0;
        break;
    case 1:
        servo = SERVO_1;
        break;  
    default:
        servo = -1;
        break;
}
switch (angle) {
    case 90:
        value = 25;
        break;
    case -90:
        value = 10;
        break;
    case 0:
        value = 14;
        break;  
    default:
        break;
}
if (servo == -1) return;
pwmWrite(servo, value);}

Rotate one servo connected to 18 (BCM GPIO)

Close others before you are going to rotate one

servo_close(1);
delay(DELAY_SERVO);

Rotate

servo(0, 90);
delay(3*DELAY_MAGIC);
servo(0, 0);

Reset all of servos to their init angles for fixing servo occasional jitter

delay(DELAY_SERVO);
servo_init();

Check more source code and informations about servo and sensor on Raspberry: MY GitHub