[time-nuts] Ebay Huawei Ublox M8T Modules Warning

[Bob kb8tq]

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> 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