[time-nuts] Ebay Huawei Ublox M8T Modules Warning

Sun Feb 21 05:34:11 UTC 2021

Hey Bob, (and whoever else has got one of these things)
I'm curious as to what degree of progress has been made using these 
little modules as-is. I know some people are pulling the M8T modules off 
to upgrade other systems but I want to try and use it as it was 
designed, as much as I can anyway.

Mine arrived today and I have been probing and poking at it off and on 
for the past 12 hours, and this is what I have found so far:

- J3 is a standard 3v3 UART running straight into the M8T. Rx (into the 
M8T) is disabled, so you need to add a jumper link to R17. It comes 
right up with NMEA at 9600 baud, but as soon as the MCU on the board 
boots up it (the MCU) sends a message that halts the NMEA. I have 
confirmed with a logic analyzer that *something* is still being sent but 
I'm not sure what, maybe ubx? It isn't much, but it happens about once a 
second.. If you disconnect the main external power and feed 3v3 in 
through this header the M8T does run as a normal standalone ublox 
package would, and I am able to modify settings.

- The M8T (maybe) can't be run off of the 3v3 UART tap alone, because 
the antenna's LNA is powered from the main power, and the antennas I use 
don't seem to like running totally passively, it's probably possible to 
just pump power into this but I haven't gone that far, yet.

- I have captured what the MCU is sending to the M8T (from monitoring 
the Rx pin on the UART header) but I haven't been able to make heads or 
tails of what it means yet.

- The pinout for J2, the main connector, as best I can tell (going off 
of what you have provided):
-- P1 - power, the docs say 15-35v, I fed in 20v and it's doing fine
-- P2 & P3 - RS422 pair for control data into the M8T
-- P4 & P6 - RS422 pair for data out of the M8T (maybe out of the MCU, I 
haven't traced this fully yet)
-- P6 - ground
-- P7 & P8 - RS422 pair for PPS

I have a few RS22/485 transceivers coming next week so hopefully I can 
confirm more of this. The HDMI pinout nokia provides is a little bit 
misleading because it includes a number of pins that are not used here, 
namely "SingleEndedIn: REF2M_IN REF10M_IN" and "GPS_PWR_RET" - this 
confused me for a little bit.

- On the bottom of the board are three chips, a 1Mbyte flash, and two 
UART-RS422/485 transceivers. Both of the transceivers are 8pin SOICs, 
one handles the control/data Tx/Rx, and the other handles the PPS. 
Something a bit curious is that one is a TI SN65HVD1474 (U3) and the 
other is a Maxim MAX3490 (U4). They have identical pinouts and very 
similar specs (20mbit vs 10mbit, respectively). Why not use two of the 
same? Vendor diversification? Manufacturer ran out of one and subbed the 
other? Curious!

- Even more curious is the way the SN65HVD1474 (U3) is configured. I 
have checked this at least two dozen times and keep coming up with the 
same results. Instead of A & B being paired, then Z & Y being paired: A 
& Y are paired, and B & Z are paired, each running the J2P7 and J2P8 
respectively. I cannot wrap my head around this. I have not yet checked 
to see what is feeding into the R & D lines of U3.

- There are three LEDs on the board, a red one which is only visible 
with the lid off that I have only ever seen illuminated, a green one 
that goes through the lightpipe to PWR, and a dual-color red/green one 
which has the following modes: flashing red 2Hz, while acquiring? 
Flashing green 2Hz (not sure, but it outputs PPS?), solid green - after 
about 20 minutes, I'm not certain.

- I have only barely started to look into the MCU, a Silicon Labs 
C8051F340. At the very least I would like to be able to dump the SPI 
flash on the back and the 8kbyte I2C EEPROM on the front. My guess would 
be that they're being used for logging and runtime, maybe calibration 
parameters? I found a C8051F340 evaluation board and it has a 10 pin 
header marked "debug", with a pinout. J7 on this board seems to be very 
close, but not identical. I'll need to dig into this one a bit more. 
Honestly, to get started, it may be as simple as holding RST high to 
just keep the MCU out of our way.

Also, I've been snapping a few pictures as I go along, they may be 
useful to others:
https://photos.millerjs.org/?f=Nokia_FYGM_GNSS

And here's a capture of what is coming out of the M8T's UART once it 
gets a solid lock:
Text: https://files.millerjs.org/Nokia_FYGM.txt
If you have Saleae Logic (free download): 
https://files.millerjs.org/Nokia_FYGM.logicdata

Regards,
John
KK4YWH

On 2021-02-04 10:01 pm, Bob kb8tq wrote:
> Hi
> 
> Again, in case anybody else is interested ….
> 
> https://www.ebay.com/itm/ON-SALE-U-BLOX-ublox-LEA-M8T-0-10-HUAWEI-GPS-Timing-Module-Board/333778776570?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
> 
> Turns out to be a bit more than what the listing implies. The parts I 
> got
> also came with a cable that goes from the round connector on the 
> assembly
> to an HDMI connector. That explains the HDMI connector pinout 
> information
> in the listing.
> 
> The big ugly “plate” turns out to be easily removed from the assembly.
> That leaves you with a nice die cast box that is roughly 3 x 2.5 x 1”. 
> It
> mounts to the plate via 4 small screws.
> 
> Since you have a cable that fits the round connector, wiring it up to 
> this or
> that should be pretty easy.
> 
> Yes, the price keeps climbing ….
> 
> Bob
> 
>> On Jan 19, 2021, at 2:43 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>> 
>> Hi
>> 
>> I don’t know if anybody else bought any of these or not.
>> 
>>> On Jan 9, 2021, at 10:20 PM, Bob kb8tq <kb8tq at n1k.org 
>>> <mailto:kb8tq at n1k.org>> wrote:
>>> 
>>> Hi
>>> 
>>> Just for the sake of listing all the variations:
>>> 
>>> https://www.ebay.com/itm/ON-SALE-U-BLOX-ublox-LEA-M8T-0-10-HUAWEI-GPS-Timing-Module-Board/333778776570?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 
>>> <https://www.ebay.com/itm/ON-SALE-U-BLOX-ublox-LEA-M8T-0-10-HUAWEI-GPS-Timing-Module-Board/333778776570?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649>
>>> 
>>> Is the M8T on what I would *guess* is the original board. Simply from 
>>> looking at the picture I think
>>> you can guess pretty well what’s what on the board.
>>> 
>>> Hint: If you buy quite a few …. errr … 10 … there s a pretty good 
>>> chance that something more than
>>> 20% might get knocked off the price …. I bought a pretty large pile 
>>> of stuff so it’s not clear if that
>>> had some impact on what offers got accepted …..
>>> 
>>> If that’s not your favorite RF connector on the board, there are 
>>> SMA’s that likely fit in the same footprint.
>>> 
>>> Bob
>> 
>> If you did, the link now goes to a new auction (at a higher price).
>> That auction shows the board in it’s proper enclosure and provides a 
>> bit
>> more ( but not quite all) information on the module. Since they are 
>> now
>> free shipping a much heavier gizmo, that might explain some of the
>> price increase.
>> 
>> If you look at the box, the connector on that box most certainly is 
>> not an
>> HDMI connector. However it *does* tell you what signals are running 
>> around.
>> You have the PPS out on RS-422. You also get the serial out of the 
>> module
>> on another RS-422 pair.
>> 
>> The clock in / clock out stuff … no idea. The EXT-INT pin on the M8T 
>> is driven
>> by the 8051 CPU on the board. It’s a good bet that’s what those clocks 
>> are getting to.
>> 
>> The TI switcher chip on the board has it’s input clamped at 20V. It 
>> puts out 6.2V. No
>> idea what the correct input is. It seemed to be very happy with the 
>> 15V I put on it.
>> Pin 1 on J1 is power in. Pin 6 on J2 is ground. Ground also shows up 
>> on one of
>> the mounting holes. The other pins on J2 appear to be 3 RS-422 pairs.
>> 
>> All of the I/O lines are protected with clamp diodes. The antenna has 
>> multiple
>> layers of protection. The debug pins on the C8051F320 come out to a 
>> connector
>> that may or may not be populated on this or that board. There is a 
>> flash chip on
>> the back side and an EEPROM on the front. If somebody was more 
>> ambitious
>> than I am, reprogramming the MCU to do fancy stuff might be possible.
>> 
>> Fun !!!
>> 
>> Bob
> 
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