Example code for talking to a servo

[shampoo]

Hi

I am looking for some example code that shows best how to talk to a servo.. If there isn't any, any ideas which example project comes the closest ?

Thanks

J

[Sigurd]

Hi,

These servos are controlled by sending a Pulse width Modulation (PWM) signal. For the nRF51 the best starting point will be the PWM Library Example. It’s located in the folder

<SDK_InstallFolder>\examples\peripheral\pwm_library 

Try with a period of 20000L, and set the duty cycle to 5% and 10% for min and max servo position.

Code snippets:

app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(20000L, PWM_PIN);




while (app_pwm_channel_duty_set(&PWM1, 0, 10) == NRF_ERROR_BUSY);

[shampoo]

Thank you.

[shampoo]

Hi

I am using the following code with no luck at all.. The servo refuses to move. I am 100% certain the hardware connections are correct and the servo does work.. Any ideas ? Here is my code:

BTW, I am using SDK 11.

int init_servo2(void)
{
	ret_code_t err_code;

	/* 2-channel PWM, 200Hz, output on DK LED pins. */
	app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(20000L, SERVO_PIN);

	/* Switch the polarity of the second channel. */
	pwm1_cfg.pin_polarity[1] = APP_PWM_POLARITY_ACTIVE_HIGH;

	/* Initialize and enable PWM. */
	err_code = app_pwm_init(&PWM1,&pwm1_cfg,pwm_ready_callback);
	APP_ERROR_CHECK(err_code);
	app_pwm_enable(&PWM1);

	uint32_t value;
	while(true)
	{
		for (uint8_t i = 0; i < 40; ++i)
		{
			value = (i < 20) ? (i * 5) : (100 - (i - 20) * 5);

			ready_flag = false;
			/* Set the duty cycle - keep trying until PWM is ready... */
			while (app_pwm_channel_duty_set(&PWM1, 0, 10) == NRF_ERROR_BUSY);

			/* ... or wait for callback. */
			while(!ready_flag);
			APP_ERROR_CHECK(app_pwm_channel_duty_set(&PWM1, 1, value));
			nrf_delay_ms(125);
		}
	}

}

[Sigurd]

Try something like this:

#include <stdbool.h>
#include <stdint.h>
#include "nrf.h"
#include "app_error.h"
#include "bsp.h"
#include "nrf_delay.h"
#include "app_pwm.h"

APP_PWM_INSTANCE(PWM1,1);                   // Create the instance "PWM1" using TIMER1.

int main(void)
{
    ret_code_t err_code;
    uint8_t SERVO_PIN = 4;

    /* 1-channel PWM, 50Hz, output on DK LED pins, 20ms period */
    app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(20000L, SERVO_PIN);

    /* Switch the polarity of the first channel. */
    pwm1_cfg.pin_polarity[0] = APP_PWM_POLARITY_ACTIVE_HIGH;

    /* Initialize and enable PWM. */
    err_code = app_pwm_init(&PWM1,&pwm1_cfg,NULL);
    APP_ERROR_CHECK(err_code);
    app_pwm_enable(&PWM1);

    uint8_t servo_pos_max = 10;
    uint8_t servo_pos_min = 5;
    while (true)
    {
        /* Set the duty cycle - keep trying until PWM is ready... */
        while (app_pwm_channel_duty_set(&PWM1, 0, servo_pos_max) == NRF_ERROR_BUSY);
        nrf_delay_ms(500);
        while (app_pwm_channel_duty_set(&PWM1, 0, servo_pos_min) == NRF_ERROR_BUSY);
        nrf_delay_ms(500);
     }

}


/** @} */

[Sigurd]

Did you change the SERVO_PIN to the pin that you are using? I used pin 4 in the code I posted. You also have a nRF52-DK? If you run the code only on the DK, does it work then?

[shampoo]

I had originally written that it was not working. But now with closer inspection something is happening. I have to put my ear to the servo and I can hear it clicking.. It's not moving, but it's clicking.. So I think we are in the right direction.

Any ideas how to get it to actually move ?