NRF52832 LED blink with timer interrup

[hyhaerong]

Hello, I am trying to make VLF~LF sinusoidal frequency (10kHz ~ 50kHz) with NRF 52832.

My approach was making a square wave first, then putting the signal into the analog rectifier circuit.

First, I tried to make a square wave by using timer delay like the following,

    while (1)
    {
		bsp_board_led_invert(3);
        nrf_delay_ms(2);
    }

and I thought it worked pretty well,

But since I request the NRF for another task, the signal has distorted like above in the middle of the signal.

Since I tried to make AM modulation/demodulation circuit with this wave, this was a huge problem for me.

I googled and found out I should approach with a timer interrupt.

So, I changed my code to the below.

int main(void)
{
    bool erase_bonds = false;
    log_init();
    timers_init();
    ble_stack_init();
    gap_params_init();
    gatt_init();
    advertising_init();
    conn_params_init();
    peer_manager_init();
  	application_timers_start();
    services_init();
    sensor_simulator_init();
    advertising_start(erase_bonds);
    csense_initialize();
	NRF_GPIO->DIRSET = 0x01 << 23;
	timerInit(50);

    while (1)
    {
//	    bsp_board_led_invert(3);
//      nrf_delay_ms(2);
			
        if (NRF_LOG_PROCESS() == false)
        {
            power_manage();
						NRF_LOG_FLUSH();
					__WFI();
        }
    }
}


void timerInit(uint16_t period_us) // function for timer init
{	
	NRF_TIMER4->TASKS_STOP	 = 1;			// stop the timer
	NRF_TIMER4->TASKS_CLEAR  = 1;			// clear
	NRF_TIMER4->MODE		 = TIMER_MODE_MODE_Timer;	// set as timer mode
	NRF_TIMER4->BITMODE		 = TIMER_BITMODE_BITMODE_32Bit; // timer counter as 32bit
	NRF_TIMER4->PRESCALER	 = 1; //prescaler as 1
	NRF_TIMER4->CC[0]		 = (float)8000000 * ((float)period_us / 1000000.0f);
	NRF_TIMER4->INTENSET	 = 65536; // timer intrupt active
	NRF_TIMER4->SHORTS		 = 0x01; // short cut register activate
	NVIC_EnableIRQ(TIMER4_IRQn); // timer interupt function activate
	NRF_TIMER4->TASKS_START  = 1;
}

However, there were 2 problems.

One is I cannot adjust the period of the signal or duty cycle.

Even if I can adjust slightly for the pulse width, I cannot change the period of the signal.

And another problem is the resolution looks really bad even though the signal was not a high frequency.

I was able to see the fall time of the pulse.

Is there any way for me so I can make a clear sinusoidal (or square) wave by using NRF52832?
What could be the problem with my code?

[Kenneth]

Hello,

Why not use the PWM for this? You can find a simple PWM example in this thead:
Is there a simple example how to set a PWM driver? 

Kenneth

[hyhaerong]

It seems this code uses delay (nrf_delay_ms) to make pulse anyway.

Which is similar to my first one (probably it could adjust the duty cycle, but it doesn't matter to me as far as I can make a 50% duty cycle signal).

Does it able to make the signal which has µs range period? I don't think (nrf_delay_ms) will take float as input.

And when I used the delay, the problem was (especially higher than a 10khz frequency range) a signal disconnection when NRF sent data through Bluetooth communication once the buffer had been filled (Figure 2).

That was the reason why I am trying to make an approach with software interrupt.

Do you think it would be okay with PWM?

[Kenneth]

hyhaerong said:

It seems this code uses delay (nrf_delay_ms) to make pulse anyway.

The delay is just there to update the PWM signal for demo purposes, the actual PWM signal is configured and controlled by the call to nrf_drv_pwm_init() and nrf_drv_pwm_simple_playback(). The PWM will run continously here independant of what the MCU may be doing in between calling the nrf_drv_pwm_* api.

Best regards,
Kenneth

[hyhaerong]

Really appreciate!

I revised the code; however, there was still an error message like the below.

.\_build\nrf52832_xxaa.axf: Error: L6218E: Undefined symbol nrf_drv_pwm_init (referred from main.o).

.\_build\nrf52832_xxaa.axf: Error: L6218E: Undefined symbol nrf_drv_pwm_simple_playback (referred from main.o).

do you think I am missing something?

[Kenneth]

You need to include the source files to your project, and add the path to the header files to your project.

Kenneth

[hyhaerong]

Thank you very much!

Actually, I enabled all the options that are relevant to the PWM, and it works now!!