[time-nuts] FE5680 GPS Disciplined Controller

Chris Albertson albertson.chris at gmail.com
Thu Jun 19 11:31:19 EDT 2014

I've been working in the same thing BUT I don't want anyone who builds it
to need a PCB.  And I want the firmware to load over USB so there is no
need to ship programmed chips or deal with external programmers.   I think
I can get the cost below $20.     That said I doubt I'll get 1E-13
performance out of my Rb.

My little Arduino based controller has been running now for a couple months
and keeping a crystal in lock.  The board has a pins left over for a serial
port that I'll hook up to the Rb.

The trick to getting the cost down is NOT to do a custom PCB.  Take
advantage of one of the uP development boards and then for under $5 you get
the USB interface, D/A and A/D, serial ports, timers and quite a bit of
logic all  1/3rd the size of a credit card.

On Thu, Jun 19, 2014 at 12:57 AM, Jan Boutsen <jan.boutsen at telenet.be>

> Count me in for an assembled and tested board. Great project.
> Jan
> ----- Original Message -----
> From: <EWKehren at aol.com>
> To: <time-nuts at febo.com>
> Sent: Wednesday, June 18, 2014 8:49 PM
> Subject: [time-nuts] FE5680 GPS Disciplined Controller
> FE5680 GPS Disciplined  Controller
> With all the FE  5680 rubidium oscillators being used as door stops out
> there some of us decided  to develop a GPSDO for it. The main question we
> have:
> Is there sufficient  interest among time nuts for a discipline controller
> for the FE5680 to make it  available? Looking at the postings over the last
> two years I am not so  sure.
> The  construction and preliminary testing of a Brooks Shera style GPS
> discipline  controller for the later version (6.81e-13 resolution) of the
> FE5680
> has been  completed. We are trying to determine the number of people that
> would be  interested in obtaining an FE5680 discipline controller (if there
> is
> sufficient  interest about $45 a kit shipping included, $75 for an
> assembled and tested  board, international orders for an additional $5)
> when
> it is
> released.
> We are also looking for three Beta  testers that would be willing to
> purchase, assemble, and test our Beta release  controller kit with their
> own
> FE5680A and GPS receiver or Tbolt and provide  feedback. Please send an
> email to
> _EWKehren at aol.com_ (mailto:EWKehren at aol.com)   Subject Time-Nuts FE 5680A,
> if you would be interested in being one of the three  Beta testers. A key
> requirement is the willingness to get to it right away, the  board assembly
> takes about 30 minutes. Instrumentation to measure results is  also a
> requirement. We obtained impressive results using a cheap ublox 6M
> receiver.
> The  FE5680 GPS discipline controller is a small (2” x 2”) board using 8
> DIP’s and 1  SOT23-5 package powered by +5v with 0.1” headers for all
> inputs
> and outputs. Our  plan is to have the kit supplier solder in the only SMD
> device on the board. A  GPS receiver 1PPS and 10 MHz sine from the FE5680
> feed the board with two 9600  baud serial ports sending TTL level tuning
> commands to the FE5680 and receiving  commands from and sending status data
> to a
> PC for data logging and system  control via a simple terminal program.
> In the chip count are  two opto couplers that allow the use of isolated TTL
> to USB conversion. These  USB adapters are readily available and furnish
> the 5 V necessary for the  secondary of the opto circuit. An option is to
> not
> use the opto couplers and  send the PIC TTL level RX and TX into a TTL to
> RS232 adapter. Another option is  to use a TTL to RS232 converter after the
> opto couplers but then an external 5 V  source would have to be supplied
> for
> the opto couplers.
> As I  mentioned before to get best performance from the FE5680 temperature
> control is  a must and after much fan and metal work I realized that a Lap
> Top heat pipe is  the easiest lowest cost solution. Comments appreciated.
> As
> an alternative the  temperature correction needs to be disabled.  Otherwise
> two control loops fight each  other.  If you look close on page 7  of the
> brochure temperature stability from –10 to +60 C looks good but a closer
> look
> and you see 4 E-11 changes over small temperature changes in the -10 to 60
> C range. Extensive analysis has been done on the FE 5680 A and maybe some
> one  can tackle that problem. Please look at what N5TNL did. It is attached
> and click  on his link. The FE 5680A does have a 4 channel MAX 1246 ADC and
> most likely it  is used to monitor temperature.
> Also  mentioned before the FE 5680 output is not the cleanest, I did
> observe it and  some one posted the attached. I apologize but my records do
> not
> show who did, so  if you posted the data please come forward. For serious
> applications where you  are using it as your main reference a clean up like
> the
> Morion MV89 or HP 10811  should be considered.
> This  addition is not required for beta tests but temperature control will
> help.
> I am also  enclosing the express PCB layout, be free to use it but it would
> be more  economical to do a group buy if there is enough interest and some
> one steps up  to kit.
> Bert  Kehren
> To  not exceed the attachment limit the plot will be a separate  posting
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Chris Albertson
Redondo Beach, California

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