[time-nuts] FE-5680A Mechanical Question

Bob Camp lists at rtty.us
Thu Jan 12 12:10:22 EST 2012


One consideration is weather / when the FE writes the DDS setting to
internal EPROM. You can easily wear out an EPROM if it's writing every time
the DDS is updated. On the flip side, having the EPROM save the last correct
value might make the "unplug and walk around" part a bit easier.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chris Albertson
Sent: Thursday, January 12, 2012 12:03 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] FE-5680A Mechanical Question

I plan to lock my FE5380 to a GPS also.  But I want to mine to "unplug
able".   The idea is to connect the GPS and let it sync for some
period of time.  Perhaps hours or maybe weeks, the longer the better
and then you can disconnect the GPS and the FE5680 free runs at that
frequency.   Plug it back in to sync it.

I think it's clear that a small micro processor is required or a
desktop computer could be used.  The FE5680 uses the RS232 port for
frequency adjustment you are going to need a computer.  I think a Tiny
AVR would do fine.  It is a $2, 8-pin chip.   It has a 10-bit A/D
converter to read the phase offset and you can use another pin for
serial output to the FE5680.  If you used a digital phase detector
you'd not need the A/D.

The controller would work like the typical GPSDO controller except
the DAC is physically inside the FE5680.  This make it easier.

Physically,  It will be mounted inside a steel box about the size of a
shoebox (The box once held a pair of large sized disk drives, from
back in the days when drives where about 3" thick)  There is a thick
aluminum plate the divides the box vertically. the FE5680 sits on top
of the plate, a heat sink is bonded to the underside of the plate.   A
low speed fan moves air through the box slowly.     The fan is
controlled by a temperature sensor bonded to the plate the FE5680 is
mounted on.   This is a crude type of "oven" using the FE5680 is a
heating element.   I hope to  stabilize temperature to about 2C.
I'll start with a simple comparator chip as a on/off fan controller
and eventually use another 8-pin uP to do a full PID controller with a
three wire fan

Chris Albertson
Redondo Beach, California

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