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 <[email protected]> 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 <[email protected]
<mailto:[email protected]>> 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
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
