[time-nuts] Synergy-GPS SSR-6tru Problem Resolved

Bob Stewart bob at evoria.net
Thu Jul 24 14:26:45 EDT 2014

Hi Tom,

I think that an offline conversation with Dusty Morris may have pointed out the root cause.  The SSR-6tru board uses 3V logic, but the Motorola Oncore boards use 5V.  So the Synergy M12 adapter has to do the level shifting to protect the receiver.  It does this for input signals by using a voltage divider composed of a 4.7K resistor on top  (for the 5V input) and a 6.8K resistor on the bottom to ground.  The center tap of these two resistors goes to the receiver.  Normally we would expect an open TTL pin to be a logic high.  But, in this case, an open pin to the 4.7K resistor on top leaves the 6.8K resistor to act as a pull-down on the receiver's input pin.  At least that's my speculation.  I'm no EE.


 From: Tom Van Baak <tvb at LeapSecond.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Thursday, July 24, 2014 12:02 AM
Subject: Re: [time-nuts] Synergy-GPS SSR-6tru Problem Resolved

Hi Bob,

That's very good news. Thanks for following through on this issue.

Newcomers to the list should know that unlike many of the large corporations in the T&F business, Synergy has been hobbyist and time-nuts friendly since the beginning. I know a couple of us bought our first GPS receivers from Synergy in the mid-1990's. This was in the early days of GPS where we used Tom Clark's TAC h/w and SHOWTIME.EXE s/w, in the same way we use Trimble's Thunderbolt h/w and Mark/John's HEATHER.EXE s/w today.


----- Original Message ----- 
From: "Bob Stewart" <bob at evoria.net>
To: "Bob Stewart" <bob at evoria.net>; "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Wednesday, July 23, 2014 3:19 PM
Subject: Re: [time-nuts] Synergy-GPS SSR-6tru Problem Resolved

As a reminder, I received an SSR-6tru receiver from Synergy, along with their M12 adapter, which allows you to plug it into a slot for an Oncore GT+, UT+, or VP. I was unable to get the receiver to respond to any commands from the u-blox u-center software.

After a lot of troubleshooting, I discovered that pin-5, the "DGPS IN" pin, must be brought to a logic level high in order for this assembly to work. If it's low, apparently anything going into the board on the Rx line is simply sent back out on the Tx line and not passed to the receiver. I've never owned a GT+ or a VP, so I wasn't aware that a logic high was needed on this pin. The UT+ works just fine with this pin not connected.


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