How to Drive RGB LED with PWM

RE: How to Drive RGB LED with PWM

Sigurd — Fri, 28 Apr 2017 07:51:00 GMT

The pins will be set to 0 voltage after you call stop_LED_glow(), but if your RGB LED is active low, the RGB LED will still glow. You can try to set the pins high in the stop_LED_glow function to test this:

void stop_LED_glow(){

    nrf_drv_pwm_stop(&m_pwm0,false);
    nrf_drv_pwm_uninit(&m_pwm0);
    
    nrf_gpio_cfg_output(gLEDR);
    nrf_gpio_pin_set(gLEDR);
    
    nrf_gpio_cfg_output(gLEDG);
    nrf_gpio_pin_set(gLEDG);
    
    nrf_gpio_cfg_output(gLEDB);
    nrf_gpio_pin_set(gLEDB);
}

RE: How to Drive RGB LED with PWM

saiteja — Fri, 28 Apr 2017 04:45:14 GMT

void stop_LED_glow(){

nrf_drv_pwm_stop(&m_pwm0,false);
nrf_drv_pwm_uninit(&m_pwm0);

}

//here R,G,B are dutycycle

void start_update_pwm(){

R = get_R();

G = get_G();

B = get_B();

for (int i=0; i<100; i++){

	reset_RGB_flag();

	update_pwm(i*R,i*G,i*B);

}

}

int main(void) {

pwm_init();
while(1){
	start_update_pwm();
	nrf_delay_ms(1000);
	stop_LED_glow();
}

}

RE: How to Drive RGB LED with PWM

Sigurd — Thu, 27 Apr 2017 13:06:02 GMT

Is the last problem solved, where you able to set a yellow light on the RGB LED?

Could you add in a comment how your "int main(void){...}" function looks like now?

RE: How to Drive RGB LED with PWM

saiteja — Thu, 27 Apr 2017 12:56:43 GMT

once i have glow led i am unable to turn it off. i have used these functions

nrf_drv_pwm_stop(&m_pwm0,false);

nrf_drv_pwm_uninit(&m_pwm0);

RE: How to Drive RGB LED with PWM

Sigurd — Thu, 27 Apr 2017 08:49:16 GMT

If you are using the code in the post I linked to, you can try this:

int main(void)
{
    
    pwm_init();
    
    update_pwm(m_top/2,m_top/2,0);

    while(1)
    {
        nrf_delay_ms(200);
    }

}

This will set the RED(12) and GREEN(14) pins to 50% duty cycle, while the BLUE(15) pin will be 0 V.

The PWM frequency is F(pwm) = base_clock/top_value, so with base clock NRF_PWM_CLK_4MHz and m_top 10000, the frequency will be ~400Hz.

RE: How to Drive RGB LED with PWM

saiteja — Wed, 26 Apr 2017 10:23:31 GMT

hi i implemented PWM driver as you said but i am unable to control the duty cycle using PWM driver. even if i change sequence values in the function

void nrf_drv_pwm_simple_playback(nrf_drv_pwm_t const * const p_instance, nrf_pwm_sequence_t const * p_sequence, uint16_t playback_count, uint32_t flags);

there is nochange. if i set set all sequence values to 0. still tricolor is displaying. how to control the duty cycle of each channel using PWM driver and how to set different values to each channel.

RE: How to Drive RGB LED with PWM

Sigurd — Tue, 18 Apr 2017 11:35:25 GMT

Hi,

You will need to create a new PWM instance to get a third channel with the PWM library. However, since you are using the nRF52832 I would recommend using the PWM driver instead(nrf_drv_pwm). This uses the PWM peripheral on the chip. Using the PWM library, app_pwm, on nRF52 you are wasting resources like timers and ppi and gpiote channels. Take a look at e.g. this devzone answer where a user configured the PWM driver for a RGB LED.

To get a yellow light you need to drive the red and green pin. You should be able to find the appropriate frequency in the datasheet for the RGB LED you are using.