Meshtastic

T-Beam GPS problems (hardware)

Support
#1

Hi… I’m sorry if this is not directly related to Meshtastic, but is a bit more related to general hardware.

I bought a ttgo t-beam and i think the gps module might be broken. I cant get any GPS data in any application, or any of the test programs or the serial pass through. I haven’t been able to get any indication that the GPS module is active at all via the serial interface.

The board version is a T22-V1.0 20190612 with a Neo-6M GPS. I’m aware that it requires the correct setup of the power management chip to enable GPS.

I also read that in some cases, the GPS chip will only work reliably at a reduced baud rate (4800), but no deal.

I tried quite a bit of fiddling with settings, pins, addresses and speeds at this point.
i’m aware that there is both https://github.com/LilyGO/TTGO-T-Beam (with an updated program for this board version) and https://github.com/Xinyuan-LilyGO/LilyGO-T-Beam.

Any ideas how i can verify that the GPS chip is … well, even reachable at this point?

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#2

I bet your problem is that the GPS is not powered. On the TBEAM there is a PMU (power management unit chip) called an AXP192. You need to tell that chip to turn on power to the GPS. If you look at meshtastic-device/src/main.cpp you’ll see an example you can copy. If you do that you can then set the TBEAM outside for 15 mins or so and the red led will start flashing (even if you never talk to the GPS). That tells you the GPS started and found satellites.

The default baud rate is 9600 bps and you should leave it at that.

#3

And also confirm you loaded the correct firmware version that relates to the TBeam.

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#4

Thanks for the answers.
I’m aware of the PMU and have already tried multiple different examples to enable the GPS chip without success.
Guess i’ll have to keep looking.

#5

I bought two T-Beam modules, both T22_V1.1 20191212 version, and one of them also appears to have a bad GPS module. The other works fine, so it could just be bad luck…

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#6

@dafeman has a good point. Even though you aren’t normally using our code. You might try installing one of our prebuilt bins (per our README). Then you could at least know if your hardware is fine (set it outside and the red led should blink)

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#7

heh, well, that was the first thing i tried of course. I have gotten the red LED to blink on some occasions.
I’m pretty sure now that my boards serial connection is somehow faulty.
Thanks again for the replies :wink:

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#8

I am looking at replacing the “ceramic gps antenna” that is shipped with all the t-beams.

  1. LilyGO Store sells a replacement, but does not really describe the antenna.
  2. I see two option “active (3v or 5v)” and passive. I assume I want “active” with the lna and filters.
  3. Various places sell these with the u.fl (or ipex) connector. sizes vary from 10mmx10mm to 25mmx25mm
    a. I find these on US amazon
    https://www.amazon.com/Ceramic-Antenna-Female-IPEX-Connector/dp/B07VKMMVKC
    or
    https://www.amazon.com/CIROCOMM-Antenna-Ceramic-25x25x2mm-Geekstory/dp/B078Y2WNY6
    or
    https://www.amazon.com/Tosuny-Antenna-Ceramic-Navigation-Interface/dp/B07QMS3M81
    or
    https://www.amazon.com/VonSom-Waterproof-Motorhome-Connector-Included/dp/B082YN5G6R

All are about $9, Does anyone have a recommendation ?

I am going to try and pry off the connector from the board per these cautions
https://learn.sparkfun.com/tutorials/three-quick-tips-about-using-ufl/all

#9

I assumed the stock gps antenna is passive. I looked at some devices that were active gps, and decided I didn’t need it yet.

#10

Both N8M and N6M can use active or passive GPS antennas. The small ceramic antennas coming with T-beam are less sensitive than the couple of real cheap active antennas I tested, which boost up GPS reception dramatically:


You would need to put a short pigtail-SMA adapter to mount an extra GPS antenna socket onto your case.

I designed a larger than usual 3D-printed T-beam box (permits to use larger screens/longer pinheaders) with a cover to receive a second SMA socket for the active GPS antenna.
When printed upside down, it permits to:

  • mount the small ceramic antenna (remove the support material and cut out the hole so the pigtail can pass, then hotglue the ceramic antenna on top which gives already a much better reception than when stuck on the battery compartment)
  • or leave the above space intact, and cut out the hole for the 2nd SMA socket for the active GPS antenna (my 3rd tT-beam setup is wired to LoRa + GPS antennas on the rooftop)
    Meshtastic_T_beam_box-Vking_v1_1-3setups
    Meshtastic_T_beam_box-Vking_v1_1-3setups863×422 108 KB

Feel free to use, modify, share…
The link to the STL files: https://www.dropbox.com/sh/iav5bai4vxluv5s/AADZT4aboAOxVr0VuBjDEtAAa?dl=0

2 Likes
#11

Thanks, I ordered the one from amazon that has the pigtail for u.fl to sma. Your setup looks good, I will have the longer gps coax to get it outside the vehicle. I like having both sma connectors to plug my antenna feeds into.

#12

Hi I bought a few STOTON high gain antennas too. They did really improve the satellite coverage and speed to fix. I have only one SMA adaptor to fit the very small tbeam sma socket so have not done too much with them yet. I exchanged the standard antenna on a tbeam T22_V1.1 with the M8N gps. It seemed to go well - I had left the battery on the device but it was switched off. It was difficult to push on the small sma on the device but I finally managed it. I have 1.1.0 loaded on the tbeam and it seemed to boot up fine - it meshes with another tbeam and connects to my app via bluetooth. It’s seen on the android app (1.1.8) as a device I can select it and it’s present on the list of devices with no ? mark against it. However if I select it then texting does not work. If I select my other meshed device then texting works to both devices. I appear to have damaged my tbeam in some way? Any thoughts appreciated. I don’t want to wreck anymore tbeams!

#13

I have the same problem with my T-Beam. Red GPS light is blinking, but no NMEA output received on the ESP32. Looking to the circuit diagram, there are two resistors R58/59 within the serial connections between ublox module and ESP32. I assume, that may be one of these resistors is not installed on the board. On the board there is a row of resistors and may be capacitors located between the ESP32 and the USB port. In my case one of these is not installed and different to photos of other those boards. But, as I do not have a layout of the board, I am not sure whether R58/59 are one in this row.

#14

I managed to solve my problem by resetting the GPS module mode using

works great since then.

There is another topic on this board somewhere but i cant seem to find it at the moment.

2 Likes
#15

Perfect - you made my day. That sketch solved my problem, too.
Thank you very much!

1 Like