Ebay find. LEA-5T-high-precision-timing-GPS-module

[jpb]

Hi,
I want to use it for a DO. I'm going to write a program to voltage adjust my Milliren 260 through a DAC. I can use a one second pulse or a 10Khz and a PPL.

Life would be simpler with the LEA-6T which has more flexible output and is available cheap currently as pointed out by Gyro (they are sold as part of a GPS compass system).

See this thread:
https://www.eevblog.com/forum/projects/my-u-blox-lea-6t-based-gpsdo-%28very-scruffy-initial-breadboard-stage%29/

[Robaroni]

I'm looking for 1E-11 to 1E-12, I don't think he got it that close.

Thanks for the link,
Rob

[Gyro]

But that's because I'm not actually _trying_ to hit those figures at the moment - my focus has been on achieving the fastest possible start-up to 'useful' accuracy by using the highest PLL frequency possible.

The LEA-6T can do anything the 5T can do, and more. There's a useful u-blox timing app-note here:

https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_%28GPS.G6-X-11007%29.pdf

[Robaroni]

I didn't buy the 5T.
Trouble is I want the simplest, cheapest solution possible. I guess I could get a 6T, make my own antenna, program it. etc. but all I really want is an accurate 1 sec pulse to compare with my rubidium every so often. The Milliren 260 and the Morion 89A really work well and the Milliren is touted to be up to rubidium standards. I built boards to 12 bit DAC precision control them through a Thevinen's equivalent circuit and I just checked the Milliren after about 4 or 5 mos. It was at 9.9999999998 compared to the last time I set it to the rubidium. So I turn on my rubidium once every six months set my OXCO's and shut it off after a day. It will probably last forever doing this and I have a couple of the Milliren 260's and one MV89A.

So bottom line, I already did all the work I want to do making the case and PCB. It was a fun project but I want to get back to making my ULE (Ultra low expansion) glass pendulum and other clocks and I only want the GPSDO to check the initial settings to see if I'm in the ball park and my rubidium isn't wacked!

I'm going to redo the boards (If anyone is interested). They work pretty good but I added the MV89A after I designed the initial circuit so I want to add a few more improvements to the final board.
The Milliren goes for about 30 bucks US on eBay but you have to watch getting bad ones and check them really well for a couple of days to make sure they hold up. If you use the internal voltage ref, make sure the ones you get don't drift.

The other problem with the Milliren is that eBay only seems to have 5 Meg versions so I used a Cypress chip to double the freq. Of course the Morion is 10Mhz so you don't need the Cypress.
Rob

[Robaroni]

Here's a built proto board with the Morion:

[Gyro]

That's impressive  As you say, you've done the hard work, and are well equipped to use just the 1pps.

The LEA-6T ebay module can easily be modified to output a 1pps signal down the existing cable as you've probably seen from the teardown. Programming via u-center s/w is easy and as the board includes both flash and ram backup battery, very easy to save to configuration. Being able to set the mark/space may or may not be useful to you.

You face the same quandary as I did - you either use the on-board patch antenna, mount the module somewhere high and buffer the 1pps signal down to where you want it (I assume you would want to buffer it to maintain timing edge integrity), or alternatively you modify it to use an external antenna.

This does seem to be the cheapest way to get the u-blox module at the moment.

[Robaroni]

Gyro,

I'll pick one up, thanks very much for the help and work you did to save the rest of us work!

Best,
Rob

[texaspyro]

The Lea 5T module has been around for a while.

What put me off is it doesn't have the variable, up to 10MHz, clock output of the Lea-6T so it is only 1PPS (I think this is the case, I may be wrong - it is hard to find old data sheets on the LEA site which now has moved beyond the Lea6T even.)

I just got in one of these boards and it does support two programmable pulse outputs.  The data sheet says you can program the width and interval in 1uS steps.  However, the data sheet does not say what range is acceptable.  I have found for the LEA-5T that anything over 1 kHz causes the pulse to go crazy or stop and the module starts dropping messages and behaving erratically.

I found the LEA-5 protocol manual on (I think) Sparkfun.  It covers the 5T specific messages.

[texaspyro]

One other thing about the board... it reports an "antenna short" condition even with no antenna connection.  The board is putting out the correct voltage on the antenna pin.

Also, I have the receiver configured to send time messages every second.  Occasionally it seems to drop a time message.  The dropped messages seem to come in clusters.  I'm running an log overnight to see what it looks like in more detail.

[Astralix]

I know this is an old thread, but as eBay disabled almost all external links, it is hard to find all information about this module.

I wonder if someone still has some pinout of the module?
If the pin near the post hole is 1 I think this might be correct:

GND  o o  ??
PPS  o o  RxD
 ??  o o  TxD
Vcc  o o  ??
       1

Does anyone have the missing pins functions for me?

Thanks!

[jpb]

I know this is an old thread, but as eBay disabled almost all external links, it is hard to find all information about this module.

I wonder if someone still has some pinout of the module?
If the pin near the post hole is 1 I think this might be correct:

GND  o o  ??
PPS  o o  RxD
 ??  o o  TxD
Vcc  o o  ??
       1

Does anyone have the missing pins functions for me?

Thanks!

The best thing might be to trace connections to the module itself.
The Lea5T datasheet is a little hard to find now but the 6T is supposed to be backwardly compatible so should have the same pin-out:
https://www.u-blox.com/sites/default/files/products/documents/LEA-NEO-6T_ProductSummary_%28UBX-13003351%29.pdf

[testpoint1]

http://www.ebay.com/itm/UBLOX-LEA-5T-high-precision-timing-GPS-module-dev-board-1PPS-USB-RS232-ntp-ser-/251785217093

5T and 6T is quite old for the 1pps timing, now can use the M8T, price is a little high if you use a second hand, 25 USD.

[Astralix]

Oh, I use two stacked double-oven Trimble modules for my 10MHz hobby lab reference. That is by far enough to adjust, even calibrate any rig that shows up for repair on my bench.
But as these Trimble units are hard to contact (FFC cables and breakout boards required) and, if in good condition, relatively expensive, I thought just for playing around, I use one of these simple modules.

This LEA-5T was less then 20EUR and so it's a perfect board to play around with ublox configuration software, rtklib and building a nice Stratum-1 NTP server for my home. As soon as I have fittet the two Trimbles in their new case, I will probably use them to run the NTP over a little OrangePi as they are powered 24/7 anyway.

But thanks Deathwish, I found that picture of the pinning that was missing in my auction.