Why am I having problems driving an RGB LED with PWM from NRF52??!

[benjamin_xo]

Hello Nordic Community.

I'm having issues trying to control a simple RGB LED circuit with the NRF52. I have set up 2 timers and PWM instances Red and Green on PWM1 and Blue on PWM2 but it's just not working. What am I doing wrong?? Here is my code (modified from the NORDIC PWM example)

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

static volatile bool ready_flag;            // A flag indicating PWM status.

bool enablePWM = true;
bool pausePWM = false;

void pwm_ready_callback(uint32_t pwm_id)    // PWM callback function
{
    ready_flag = true;
}


int main(void)
{
  uint32_t err_code;

    // Create the instance "PWM1" using TIMER1.
    APP_PWM_INSTANCE(PWM1,1);      
    // Create the instance "PWM2" using TIMER2.
    APP_PWM_INSTANCE(PWM2,2);             

    // RGB LED pins
    // (Common cathode)
    uint32_t pinR = 12;
    uint32_t pinG = 14;
    uint32_t pinB = 15;
   
    // 2-channel PWM, 200Hz
    app_pwm_config_t pwm1_cfg = 
      APP_PWM_DEFAULT_CONFIG_2CH(5000L, pinR, pinG);

    /* Initialize and enable PWM. */
    err_code = app_pwm_init(&PWM1,&pwm1_cfg,pwm_ready_callback);
    APP_ERROR_CHECK(err_code);
    app_pwm_enable(&PWM1);     
 
    // 1-channel PWM, 200Hz
    app_pwm_config_t pwm2_cfg = 
      APP_PWM_DEFAULT_CONFIG_1CH(5000L, pinB);

    /* Initialize and enable PWM. */
    err_code = app_pwm_init(&PWM2,&pwm2_cfg,pwm_ready_callback);
    APP_ERROR_CHECK(err_code);
    app_pwm_enable(&PWM2);

    uint32_t value;
    while(1) {

        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, value) == NRF_ERROR_BUSY);

            nrf_delay_ms(25);
        }

         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, 1, value) == NRF_ERROR_BUSY);

            nrf_delay_ms(25);
        }

         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(&PWM2, 0, value) == NRF_ERROR_BUSY);

            nrf_delay_ms(25);
        }

    }

}

[awneil]

it's just not working

Tells us nothing.

• What, exactly, were you expecting to happen?

• What, exactly, is actually happening?

• What testing/debugging have you done to explain the difference?

www.catb.org/.../smart-questions.html

[Ole Bauck]

Since you are using nRF52 you should consider using the PWM driver, nrf_drv_pwm instead. 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. Here is a snippet of code that sets the pwm driver to one duty cycle: devzone.nordicsemi.com/.../

If you want to find out what is the problem with the code you are running now with app_pwm, you should go into debug mode and check that all the error codes are NRF_SUCCESS.

[benjamin_xo]

Thanks Ole and Awneil for your feedback. I used the PWM Driver instead as you suggested Ole and it worked perfectly. Here is my code which plays a test animation on 3 LEDS.

#include <stdio.h>
#include <string.h>
#include "nrf_drv_pwm.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "boards.h"
#include "bsp.h"
#include "app_timer.h"
#include "nrf_drv_clock.h"
#define NRF_LOG_MODULE_NAME "APP"
#include "nrf_log.h"
#include "nrf_log_ctrl.h"

#include "nrf_delay.h"

#define APP_TIMER_PRESCALER     0
#define APP_TIMER_OP_QUEUE_SIZE 2

int gLEDR = 12;
int gLEDG = 14;
int gLEDB = 15;

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);
// static nrf_drv_pwm_t m_pwm1 = NRF_DRV_PWM_INSTANCE(1);
//static nrf_drv_pwm_t m_pwm2 = NRF_DRV_PWM_INSTANCE(2);

static uint16_t const m_top  = 10000;


//static nrf_pwm_values_individual_t  /*const*/ seq_values;
static nrf_pwm_values_individual_t  /*const*/ seq_values;
static nrf_pwm_sequence_t const seq =
    {
        .values.p_individual = &seq_values,
        .length              = NRF_PWM_VALUES_LENGTH(seq_values),
        .repeats             = 0,
        .end_delay           = 0
    };


static void pwm_init(void)
{
    uint32_t err_code;
    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {
            gLEDR,// channel 0
            gLEDG, // channel 1
            gLEDB, // channel 2
            NRF_DRV_PWM_PIN_NOT_USED  // channel 3
        },
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .base_clock   = NRF_PWM_CLK_4MHz,
        .count_mode   = NRF_PWM_MODE_UP,
        .top_value    = m_top,
        .load_mode    = NRF_PWM_LOAD_INDIVIDUAL,
        .step_mode    = NRF_PWM_STEP_AUTO
    };
    err_code = nrf_drv_pwm_init(&m_pwm0, &config0, NULL);
    APP_ERROR_CHECK(err_code);
    // m_used |= USED_PWM(0);

        // This array cannot be allocated on stack (hence "static") and it must
    // be in RAM (hence no "const", though its content is not changed).
}

void update_pwm(int16_t dutyR, int16_t dutyG, int16_t dutyB)
{
    
    seq_values.channel_0 = m_top-dutyR;
    seq_values.channel_1 = m_top-dutyG;
    seq_values.channel_2 = m_top-dutyB;
    

    //seq_values = duty_cycle;

    //nrf_drv_pwm_simple_playback(&m_pwm0, &m_seq, 1, 0);
    //nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 1, NRF_DRV_PWM_FLAG_LOOP);
    nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 1,  NRF_DRV_PWM_FLAG_LOOP);
}

int main(void)
{
  
  pwm_init();

    while(1){

        for (int i=0; i<100; i++){
            update_pwm(i*100,0,0);
            nrf_delay_ms(1);
        }

        for (int i=0; i<100; i++){
            update_pwm(10000,i*100,0);
            nrf_delay_ms(1);
        }

        for (int i=0; i<100; i++){
            update_pwm(10000,10000,i*100);
            nrf_delay_ms(1);
        }

        for (int i=100; i>0; i--){
            update_pwm(i*100,10000,10000);
            nrf_delay_ms(1);
        }

        for (int i=100; i>0; i--){
            update_pwm(0,i*100,10000);
            nrf_delay_ms(1);
        }

        for (int i=100; i>0; i--){
            update_pwm(0,0,i*100);
            nrf_delay_ms(1);
        }

        update_pwm(0,0,0);
        nrf_delay_ms(200);

        
   
    }


    
}
/**/

[saiteja]

hi, i am running your application, if i give duty value in a function like update_pwm(0,0,0) it is still showing tri color. and also i am unable to uninit and unable to stop glowing LED once i glow LED.