PWM modulation frequency or modulation amplitude

RE: PWM modulation frequency or modulation amplitude

creator — Mon, 12 Nov 2018 05:54:03 GMT

Thank you for your reply, you can change the frequency output.

RE: PWM modulation frequency or modulation amplitude

Sigurd — Wed, 07 Nov 2018 14:56:29 GMT

The driver does not support it, but you could try to set the COUNTERTOP register directly in the handler. The duty cycle will also change if you only increase the top_value, so if you want the duty cycle to be the same, you will need to update the seq_value also. You will also need to add some RC filter, or similar to the pin output to get the desired output shown in the image you uploaded.

Snippet:

static nrf_pwm_values_individual_t seq_values_new;
static void demo1_handler(nrf_drv_pwm_evt_type_t event_type)
{
    if (event_type == NRF_DRV_PWM_EVT_FINISHED)
    {
        uint32_t current_mtop = NRF_PWM0->COUNTERTOP;

         if(current_mtop < 32767 )
         {
            NRF_PWM0->COUNTERTOP = current_mtop + 100;

            seq_values_new.channel_0 = NRF_PWM0->COUNTERTOP /2;

            nrf_pwm_values_t new_pwm_values; 

            new_pwm_values.p_individual = &seq_values_new;

            nrf_drv_pwm_sequence_values_update(&m_pwm0,1,new_pwm_values);

         }

    }
}

RE: PWM modulation frequency or modulation amplitude

creator — Tue, 06 Nov 2018 03:00:31 GMT

Hello, thank you for your reply. It's known that you want to change. top_value = m_demo1_top. This value needs to be restarted to the initial pwm. I don't know if it's right. How to restart the initial pwm? Is it okay to start the PWM in the interruption?

RE: PWM modulation frequency or modulation amplitude

Sigurd — Mon, 05 Nov 2018 08:45:01 GMT

Hi,

The desired pwm frequency is given by the formula F(pwm) = F(base_clock) / top_value. So your idea of increasing the m_demo1_top is correct. Note that the max top_value is 32767.

[quote user=""]M_demo1_top is added from zero to 10000, but no PWM has no output.[/quote]

When does this happen? When M_demo1_top reaches 10000?