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I have a microcontroller board Datagnss Tiny EVK with an integrated chip TAU1302 (Allystar). I can get a fix with expensive Tallysman antennas in a rural area, with over 30 satellites and SNRs exceeding 40. I can see L1 , L2C, and L5 bands , at will.

A blue LED is supposed to light up indicating that the PPS signal is pulsing after a fix. I have never seen this blue LED turn on, ever. All documention, guides and datasheets for this module indicate that it should simply come on after a fix. I have never seen this happen. With oscilloscope, I measure the PPS line from a molex launch. It is always emitting a 2.5V square wave at 60Hz. It emits that no matter the condition -- indoors, outdoors, fix, no fix. So I know my mechanical circuits are correct.

How do I make this module begin to output PPS? Do I need to send a command of some kind through the RX/TX serial? If anyone has seen something similar with UBlox GNSS modules, please leave a reply, even if it does not match my hardware exactly.

TAU1302 Board

molex launch to PPS

Ksenia Semenova
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  • this might help: https://raspberrypi.stackexchange.com/questions/130705/pico-pi-rtc-interrupt/140932#140932 – tlfong01 Mar 10 '23 at 05:38
  • usually no fix = no pps, fix = pps. All automatic, no Rx/Tx is needed. – tlfong01 Mar 10 '23 at 05:51
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    tlfong01 Your answer is absolutely wrong. I have multiple fixes on dozens of satellites. I am getting multiple types of NMEA sentences and location data, and even some RAW data. There is no PPS LED turning on. The PPS line emits 2.5 volt square waves at 60Hz. It even continues doing that after I rip the antenna off. – Ksenia Semenova Mar 10 '23 at 05:55
  • Well, my answer is based on my experience on Ublox M6/7/8/10. I have no experience on AllyStar. Perhaps I should read the AllyStar doc to see if there is any difference. ***Multi-Band GNSS Raw Data Module TAU1302 Datasheet V1.5 - AllyStar 2021*** https://docs.datagnss.com/rtk-board/files/T-5-2107-TAU1302%20Datasheet-V1.5.pdf – tlfong01 Mar 10 '23 at 06:03
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    @tlfong01 you usually have to enable that through some command to the firmware, or have some firmware that enables it by default. Deriving a PPS from your satellite observation isn't "free" in terms of electricity used, so that GPS receivers based on firmware that's not primarily focused on timing applications might not do it by default. – Marcus Müller Mar 10 '23 at 09:10
  • @Marcus Müller: I agree with you. So, it is a tradeoff between saving energy and newbie friendliness. I vaguely remember that the designers of the cheapie GPS modules I have tested so far choose to be newbie friendly, and enable status LED. – tlfong01 Mar 10 '23 at 10:42
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    GPS receivers are internal components with a user guide that needs to tell you how to use them, anyways. I don't think "newbie friendliness" is a big consideration when you need to read the documentation, no matter how newb you are! Really, my experience is that the PPS output is enabled by default if the vendor thinks that's a feature desirable to whoever they hope will buy these things. – Marcus Müller Mar 10 '23 at 10:58

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