How can i add more pwms in nrf52840 example

[akay47]

I am working on CAF example Module and it has 4 pwms in overlay file.

1. Is it possible to add another PWM?

2. Is there any limit to number of PWMs and number of channels i can use on each pwm?

3. Can you please point me to any resource available?

4. Also how can i add more channels in single pwm?

[Simonr]

Hi

1. Yes, that should be possible.

2. There are 4 PWM channels, and 4 PWM instances available on the nRF52840, so there are a total of 16 pins can be used for PWMs, but with some limitations for the ones sharing instances/channels. https://docs.nordicsemi.com/bundle/ps_nrf52840/page/keyfeatures_html5.html 

3. The product specs and the https://docs.nordicsemi.com/ in general should be helpful. Also, the nRF Connect SDK courses on the DevAcademy should be of use.

4. I'm not sure I understand your question here. What is the use case you need this for exactly?

Best regards,

Simon

[akay47]

Thank you for your response. I am working on CAF module example and it has 4 pwm configured. correct me if i am wrong,
1. but i believe those are 4 unique PWMs where each PWM can has 4 different channels.
2. Each PWM can be set to a unique frequency and all channels of that PWM will share same frequency?
3. The only thing channels on a single PWM can have different is Duty cycle?
4. Now i want to modify that example to add more channels in a single PWM Instance so i can provide those signals to an RGB LED with different duty cycles on 3 channels of a single PWM Instance for color mixing. I could not find any example on how to do that.

[Susheel Nuguru]

Answers to your questions

akay47 said:

1. but i believe those are 4 unique PWMs where each PWM can has 4 different channels.

Yes,  Can see instances here and four channel count which can be used in the nrfx_pwm_config as below

nrfx_pwm_config_t const pwm_config = {
    .output_pins = { 22,                      // Channel 0 pin (set to your desired GPIO pin)
                     NRF_PWM_PIN_NOT_CONNECTED, // Channel 1
                     NRF_PWM_PIN_NOT_CONNECTED, // Channel 2
                     NRF_PWM_PIN_NOT_CONNECTED }, // Channel 3
                     ....

akay47 said:

3. The only thing channels on a single PWM can have different is Duty cycle?

Yes, that is correct. In the nRF52840 PWM peripheral, all channels within a single PWM instance share the same frequency and period (top value), but they can have individual duty cycles

akay47 said:

Now i want to modify that example to add more channels in a single PWM Instance so i can provide those signals to an RGB LED with different duty cycles on 3 channels of a single PWM Instance for color mixing. I could not find any example on how to do that

Yes, Something like this

nrfx_pwm_t pwm_instance = NRFX_PWM_INSTANCE(0); // Use PWM instance 0

nrfx_pwm_config_t const pwm_config = {
    .output_pins = { X,   // Red LED pin (Channel 0)
                     Y,   // Green LED pin (Channel 1)
                     Z,   // Blue LED pin (Channel 2)
                     NRF_PWM_PIN_NOT_CONNECTED }, // Channel 3 is not used
    .irq_priority = APP_IRQ_PRIORITY_LOWEST,
    .base_clock   = NRF_PWM_CLK_1MHz,  // 1 MHz base clock
    .count_mode   = NRF_PWM_MODE_UP,
    .top_value    = 1000,              // Adjust for PWM frequency (e.g., 1 kHz)
    .load_mode    = NRF_PWM_LOAD_INDIVIDUAL,
    .step_mode    = NRF_PWM_STEP_AUTO
};