BLE + PWM motor driver

[ypearson]

The project I'm using the peripheral BLE UART that has been modified to use freeRTOS and PWM.

I'm using two channel PWM to drive a resonance motor at 25.6 kHz. If I disable the BLE thread the standard deviation of the PWM signal is ~10 Hz. However if the BLE thread is enabled, the PWM standard deviation jumps to ~ 150Hz. And unfortunately that is enough of a frequency drift to bring the motor out of resonance. Is there anything I can do to minimize this effect, and why does BLE increase the drift of the PWM signal ?

The PWM base is 16 MHz

thanks,

[ypearson]

@Torbjørn Øvrebekk That worked, here is the lines of code that I used to fix it

// Start the external high frequency crystal
NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
NRF_CLOCK->TASKS_HFCLKSTART = 1;
// // Wait for the external oscillator to start up
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) {}

[ovrebekk]

That's the way to do it. I am glad to hear this solved your issue :)

[Namklak]

Yes, no more jitter.  But when I'm done with motion, I'd like to put the hfclk back in control of the ble softdevice, for minimum power use, how do I do that?

[ovrebekk]

Hi 

When using the SoftDevice you should use the sd_clock_hfclk_request() function to enable the external HF crystal, and the sd_clock_hfclk_release() function to release it.

Best regards
Torbjørn