How to make a beep on nRF51822 with BLE SD and what timer to use?

Question

Hi,
I need to drive a piezo buzzer. Just need to make a simple beep function(s) that one call will start generating a specified frequency on specified pin and other call will stop it. Desired freq. is about 3,5kHz. So I would use some timer thats output can be redirected to a GPIO and simply set a prescaller and run it. I even don't need PWM just toggle a pin. What timer can I safely use together with BLE SD?
I already have one timer used for scheduler in my code
static void timers_init(void)
{
APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_MAX_TIMERS, APP_TIMER_OP_QUEUE_SIZE, true); // v app_timer.h
}
What API functions I should use for this - is there some simple example?

Martin · Accepted Answer

OK, seems that I found usable piece of code - the timer-driven LED in module LED.C from ble_app_hrs project. It use timer1 and PPI channel 0 that should be free with BLE SD. I just had to change prescaler and timer compare value to be set according to desired frequency and it seems that it works...