GPS 1PPS on nRF9151 DK

RE: GPS 1PPS on nRF9151 DK

Yun531 — Mon, 30 Jun 2025 17:34:33 GMT

I figured out the solution from this forum post. I need an external pull-down resistor on the COEX1 pin (or any COEX pins that I'm planning to use).

I wish the document could indicate this better. From the document, I thought that only the COEX2 pin needs an external pull down resistor.

Also, for anyone having a simlar use case, if using the 1 time pulse mode and single fix operation. I need to wait for a certain time (I wait for 100 ms) before disable 1PPS. If I disable 1PPS immediately after a fix (in NRF_MODEM_GNSS_EVT_FIX), the pulse will not be generated.

RE: GPS 1PPS on nRF9151 DK

Yun531 — Fri, 27 Jun 2025 21:30:42 GMT

I tried to enable 1PPS but I have no luck so far.

I followed one of the sample from Nordic Cellular IoT Course (Lesson 6 Exercise 1) to enable GPS only. I use the same code as this exercise, and I added 1 PPS:

/* 1PPS pulse on COEX1 */
struct nrf_modem_gnss_1pps_config config = {
    .pulse_interval = 120,
    .pulse_width = 500,
    .apply_start_time = false
};

/* In main right before nrf_modem_gnss_start */
err = nrf_modem_gnss_1pps_enable(&config);
if (err != 0) {
    LOG_ERR("Failed to enable 1 PPS, error %d", err);
    return -1;
}

I attached the main.c file here as well.

devzone.nordicsemi.com/.../0310.main.c

I'm able to get a fix from GPS, but the COEX1 pin is not pulsing. I open the board configurator and enable this option:

Then I connect the COEX1 pin from the nRF9151 DK to the oscilloscope, and there is no pulse. I don't know what I'm supposed to do to make the COEX1 pin to start pulsing. Any suggestions or help would be greatly appreciated. Thank you.

RE: GPS 1PPS on nRF9151 DK

Yun531 — Tue, 24 Jun 2025 05:09:59 GMT

Hi,

If there is no sample for using the COEX1, is there any sample or general guide on how to enable and disable LTE manually?

I'm currently working through the Cellular IoT Fundamentals course and so far, the exercises for LTE and GNSS to be active at the same time is enable GNSS when the LTE is in power saving mode (Lesson 6 exercise 2). My SIM does not support PSM or eDRX, and here's a note from the lesson:

If your network operator and/or SIM card does not support either PSM nor eDRX, you will have to manually deactivate and activate the modem when wanting to use the GNSS in your application. There is a workaround, by giving the GNSS priority over LTE events to help get a fix. This is not recommended, as it interferes with LTE operations.

Could you help me with this? Especially, there is a "keep alive" while true loop in main, I'm unsure on how to manually deactivate/activate the modem in conjunction with this loop.

If helpful, here are the links that I refered to:

GNSS Lesson 6 Exercise

RE: GPS 1PPS on nRF9151 DK

Hakon — Mon, 16 Jun 2025 10:56:56 GMT

[quote user="Yun531"]Since the document said this is an output pin, I can wire it back to the GPIO and treat it as an interrupt? Is there a way for the DK to automatically know this without any additional wiring (such as enabling some Kconfig option)?[/quote]

Yes, you can use GPIO pin on your host MCU and configure an interrupt to know when activity occurs. That seems like the best option as far as I am concerned.

[quote user="Yun531"]Is there a way for the DK to automatically know this without any additional wiring (such as enabling some Kconfig option)?[/quote]

I don't know how that would be possible.

RE: GPS 1PPS on nRF9151 DK

Yun531 — Thu, 12 Jun 2025 14:30:50 GMT

Hi Hakon, thank you for your response. These are the sources I linked in my original question as well. My confusion is how to use the COEX1 pin? Since the document said this is an output pin, I can wire it back to the GPIO and treat it as an interrupt? Is there a way for the DK to automatically know this without any additional wiring (such as enabling some Kconfig option)?

RE: GPS 1PPS on nRF9151 DK

Hakon — Wed, 11 Jun 2025 13:04:40 GMT

Hello,

it should be possible to enable this on the nrf9151. Check out this part of the documentation.

1PPS can be accessed on the COEX1 pin on the nrf9151, P24 pin2 on the DK. You should read the details about the COEX interface. Also, importantly make sure that LTE is disabled during 1PPS operation on COEX1.

I was unfortunately not able to find a proper sample for this.