A simple PWM LED approach for the Thingy:91

RE: A simple PWM LED approach for the Thingy:91

Albrecht Markus Schellenberger — Fri, 14 May 2021 07:07:23 GMT

Thanks a lot for the feedback, Christopher! I am pleased to hear that your application works now :-)

Cheers!

Markus

RE: A simple PWM LED approach for the Thingy:91

Christopher Hunt — Thu, 13 May 2021 07:12:01 GMT

Just to close this off, all now appears well. I'm thinking that something just got "stuck" somewhere... After building and flashing the Zephyr example again, I then erased the board, added the spm and flashed my Rust code. It works! Thanks for your help. I'll mark your initial reply as the answer as it helped.

RE: A simple PWM LED approach for the Thingy:91

Christopher Hunt — Wed, 12 May 2021 08:36:40 GMT

OK, I tried 50% of the max duty. No cigar.

Would I be pushing the friendship to show you the code in full? :-)

github.com/.../blinky.rs

RE: A simple PWM LED approach for the Thingy:91

Christopher Hunt — Wed, 12 May 2021 07:36:44 GMT

I can make the lights now blink on the nRF9160-dk with the max duty cycle. I'll try again with the Thingy:91 and 50% of the max. I'll get back to you shortly. Thanks.

RE: A simple PWM LED approach for the Thingy:91

Albrecht Markus Schellenberger — Wed, 12 May 2021 07:18:33 GMT

Hello Christopher,

the Zephyr example uses a duty cycle of 50% changing the frequency up- and downwards. The maximum frequency is dependent on the wave counter and its prescaler, which is why the “self-calibration” was added to this application.

Could you elaborate what kind of issue you exactly have? Are you able to make the LEDs blink at all?

Regards,

Markus

RE: A simple PWM LED approach for the Thingy:91

Christopher Hunt — Tue, 11 May 2021 12:59:41 GMT

OK, I confess. I'm using Rust. :-) I've had a lot of success using Rust with other Nordic hardware and so I'm now trying to get board support happening with the Thingy:91. By point 3, here's the code:

    rprintln!("PWM Blinky demo starting");
    loop {
        pwm.set_duty_on_common(pwm.get_max_duty());
        delay(&mut timer, 250_000); // 250ms
        pwm.set_duty_on_common(0);
        delay(&mut timer, 1_000_000); // 1s
    }

And here's the setup:

fn init_device(p: hal::pac::Peripherals) -> (Pwm<hal::pac::PWM0_NS>, Timer<hal::pac::TIMER0_NS>) {
    let p0 = gpio::p0::Parts::new(p.P0_NS);

    let pwm = Pwm::new(p.PWM0_NS);
    pwm.set_output_pin(
        pwm::Channel::C0,
        &p0.p0_02.into_push_pull_output(gpio::Level::High).degrade(),
    );

    let timer = Timer::new(p.TIMER0_NS);

    (pwm, timer)
}

The Zephyr code you referred to actually does something interesting with the max duty value. It appears as though it keeps halving it until setting the duty is accepted. Perhaps that's what I need to do here.

RE: A simple PWM LED approach for the Thingy:91

Albrecht Markus Schellenberger — Tue, 11 May 2021 11:29:17 GMT

Hello Christopher,

Since you are not using Zephyr in your application, I assume that you are using the pwm_nrfx drivers directly?

I’m not quite sure if I understand point 3, though. Can you elaborate? Thanks!

Regards,

Markus

RE: A simple PWM LED approach for the Thingy:91

Christopher Hunt — Mon, 10 May 2021 14:03:29 GMT

Do those settings of mine also look right though (I'm not using Zephyr in my own app)

RE: A simple PWM LED approach for the Thingy:91

Christopher Hunt — Mon, 10 May 2021 14:02:24 GMT

Thanks - that worked!

RE: A simple PWM LED approach for the Thingy:91

Albrecht Markus Schellenberger — Mon, 10 May 2021 13:26:37 GMT

Hello Christopher,

Zephyr provides a straightforward sample showing how to control an LED with a PWM peripheral.

You can find it in your ncs folder: ../zephyr/samples/basic/blinky_pwm.

It doesn’t work for the Thingy:91 from scratch, but you can easily get it to work with the following modifications:

Create an overlay file in your application root called: thingy91_nrf9160ns.overlay
Add the following lines to the overlay file

/ {
    pwmleds {
        compatible = "pwm-leds";
        pwm_led0: pwm_led_0 {
            pwms = < &pwm0 0x1f >;
        };
    };

    aliases {
        pwm-led0 = &pwm_led0;
    };
};

Build and run

The application should now trigger the blue LED colour of the lightwell LED.

I hope this is a good starting point for you!

Regards,

Markus