[time-nuts] Trimble GPS board

Arthur Dent golgarfrincham at gmail.com
Mon Aug 24 08:14:18 EDT 2015

Bob Camp wrote: "There’s also this listing that shows
an pair of 9 pins tacked on the same board:"
If you look closely that is a daughter board the seller made
that is mounted on top of the Trimble board. Some of the
listings use the 50-pin ribbon cable connector to connect to
some form of interface board they have.

I should clear up some previous statements that I made that
were inarticulate and lead to some confusion. When I wrote:
"The supply voltage required is stated to be 5.6 to 6VDC and
this goes to an LT1764A low dropout regulator set to 5VDC out
so my 'guess' is that 6VDC should be the minimum supply voltage
to make sure the regulator keeps working properly.", I actually
meant the supply should be 6VDC-period. You don't have to get
into higher math to determine what voltage to use. As to the
current the oscillator (or the entire board) draws, at start-up
it is 2A as one of the Ebay listings states. As the oven warms
up this dropped to about 0.8A on each of the 2 boards I have.
The specs for the LT1764A shows the minimum differential agree
pretty much with what I had measured. At power-up it was about
0.4VDC and warmed-up it was about 0.2VDC. I measured the dropout
voltage to be less than 5.4V warm. Using a common wall-wart fixed
regulated power supply of 6VDC is a common sense decision. I
would not try using anything higher, even not knowing as Angus
(not.again at btinternet.com) pointed out, there are circuits
that are powered by the input voltage before it goes through
the LT1764A. Quite often you can find an adequate 6VDC power
supply at the local Goodwill or at a fleamarket.

Anyone buying just the board and trying to find a nice enclosure
to build it into might want to check out Ebay item 250597854445
which appears to be a (6" x 4.1" x 2.2") black extruded aluminum
case identical in style to what is used in some of the ready made
units. Also check Ebay 351340026725 for some 6" MCX to SMA panel
mount cables that look like the ones they use with some of the
GPSDOs you see on Ebay. Note I have no connection (pun) with these
sellers but I have ordered these items to use with the 2 board-
only units I bought at $42.90 each (including shipping). I also
plan to remove the two 2-color LED from the underside of the pc
board and mount 2 others LEDs on the front panel to let me see
what the unit is doing. I'll probably move the reset switch as well.

Another note is to check the listings carefully because the price
seems to change frequently on some of the listings for these
Trimble units. After I bought the 2 I wanted the price on that
listing jumped to $48 then to $61 and the quantity dropped to zero.
Also if you don't want to be cheap like me and go through the hassle
of building your own unit from scratch (although it is a learning
experience), you can buy the complete package from some sellers for
about $150. Finally keep in mind that most of the info in this
thread is preliminary and like many have pointed out, may still
have errors. We're all trying to make it easier for others but
we ain't perfuct!


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