[time-nuts] FE-5680B Rubidium and DDS

Wed Sep 30 19:54:51 UTC 2015

Clint, Yes, same seller. Yes schematic is partial, but it did answer a question for me that I posted on eevblog where others suggested removing a number of components to feed the 20Mhz to a divider. Looks like its a resistor, cap and inductor from the schematic; R1,C1,L1.
I see, you want to make a easily reprogrammable frequency generator. I haven't looked at the datasheet of  the AD9851, but thought it needed a 125Mhz crystal. Probably just easier to use a circuit like this.
http://www.perdrix.co.uk/FrequencyDivider/index.html

http://www.ka7oei.com/FE-5680_diag_1c.gif   (would still need to divide first)
I was planning on the same, but just using the /2 for a 10Mhz out in the first link.
Was always hoping for a easy mod inside the "B", but from the write up that was just posted, the author has scoped it pretty well and it appears the disappearing 10Mhz appears to be firmware driven. 
Cheers

-=Bryan=-

> Date: Wed, 30 Sep 2015 11:45:49 +0100
> From: cjaysharp at gmail.com
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] FE-5680B Rubidium and DDS
> 
> Bryan, I think we do, bought from an eBay seller named Fluke.I?
> 
> I also found that schematic but it's a partial, very useful nonetheless.
> 
> There's also a dump of the firmware and CPLD so I'm hoping I can make some
> sense of that to work out the CPLD, I'd be happy with a solid 10MHz output
> but to my mind, if I can clock an AD9851 with the 30MHz signal I can get
> 'as good as' with the same or better performance to the serially
> programmable DDS module.
> 
> My thinking may of course be flawed, I'm new to the whole time nut game and
> am learning as I go.
> 
> The M09 chip seems to be in place of the MAX3232 chip, coupling RX/TX from
> connectors to the CPU, it may be an opto but the package is tiny so it'd
> not offer much isolation, I'll take another look this evening and work out
> the connections fully.
> 
> On 29 September 2015 at 21:06, Bryan _ <bpl521 at outlook.com> wrote:
> 
> >
> >
> >
> > Hi Clint:
> > Looks like we have the identical board. I suspect the XC9572 is turning
> > off the 10Mhz, although why would it wait for 6 seconds?. And as you say
> > it's not related to the "lock" . Here is a schematic I found for a FE-5680A.
> >
> > http://www.rhodiatoce.com/pics/time-nuts/FE-5680A/FE-5680A_schematics_v0.1.pdf
> > I also note the same strange chip in the middle of the absent Max233,
> > wonder if it is some type of optoisolator to protect
> > inputs/outputs?Although not sure why one would be needed if the MAX232 is
> > unpopulated.
> >
> > -=Bryan=-
> >
> > > Date: Tue, 29 Sep 2015 15:41:37 +0100
> > > From: cjaysharp at gmail.com
> > > To: time-nuts at febo.com
> > > Subject: Re: [time-nuts] FE-5680B Rubidium and DDS
> > >
> > > I've made some investigations and re-confirmed my earlier findings on the
> > > FE-5680B I have.
> > >
> > > It locks from cold in under five minutes and runs at approximately 700mA
> > > steady with the expected PPS signal on the output connector when locked.
> > >
> > > The particular 5680 I have has a Hi Density 15p male connector on the
> > > output and uses a single 15V supply, part number FE5680B UN 77672.
> > >
> > > The device does not have the optional DDS daughterboard which means that
> > > it's not usable as a programmable signal source as it stands (but see
> > > later).
> > >
> > > For approximately six seconds after power is applied a 10MHz signal
> > > available on the output connector, this signal comes directly from the
> > > XC9572 CPLD via a filter network and appears to be a clean sine wave.
> > >
> > > The 10MHz signal seems to be 'switched off' by some event in the unit, I
> > > don't yet know if this is in response to an event or just a timed
> > shutdown
> > > but power cycling the unit re-enables the 10MHz output for a further six
> > > seconds. It doesn't appear to be related to rubidium lock as it takes
> > > consdierably longer than six seconds to lock.
> > >
> > > There is a solid 30MHz signal inside the unit, stable once the rubidium
> > has
> > > locked and the PPS output is also available once locked.
> > >
> > > Other observations show that the MAX3232 serial driver chip is missing
> > and
> > > in it's place there is a tiny 8 pin device marked M09 or MO9 which is
> > > connected to the TXD/RXD pins on the output connector and the TXD/RXD
> > pins
> > > on the 80C323 CPU.
> > >
> > > I'd be very interested in suggestions as to the part number of that
> > device,
> > > it may yield clues as to the communication method needed.
> > >
> > > Attempts to communicate with it via a terminal program have given no
> > > responses at several 'standard' baud rates. Voltage levels are LVTTL.
> > >
> > > I'm wary of applying 5V to any of the pins on the interface connector
> > > directly and probing them with 3.3v via a 10K resistor has made no
> > > difference to any of the signals I can monitor (30MHz, PPS etc.) with the
> > > exception of pin 13 which I *think* is reset, obviously this causes the
> > > frequencies to skew for a few seconds until reset is completed.
> > >
> > > My intent is to use the 30MHz signal from the CPLD to clock a DDS chip
> > > (probably one of the eBay DDS modules) that's controlled by a PIC chip (I
> > > already have code to run a DDS VFO I developed earlier this and late last
> > > year. Hopefully this will be small enough to fit inside the casing
> > though I
> > > don't see a problem with bringing the 30MHz signal out if necessary.
> > >
> > > My apologies if this is outside of the scope of this list, I will also be
> > > writing up my findings and experiments with this standard on my blog if
> > > anyone is interested?
> > >
> > >
> > >
> > > On 26 September 2015 at 11:23, Bryan _ <bpl521 at outlook.com> wrote:
> > >
> > > > Thanks Hal, that's interesting, will try and see how far I can get.
> > > > -=Bryan=-
> > > >
> > > > > To: time-nuts at febo.com
> > > > > From: hmurray at megapathdsl.net
> > > > > Date: Fri, 25 Sep 2015 23:40:40 -0700
> > > > > CC: hmurray at megapathdsl.net
> > > > > Subject: Re: [time-nuts] FE-5680B Rubidium and DDS
> > > > >
> > > > >
> > > > > > I as well wish there was a quick way of converting it back to
> > 10Mhz. I
> > > > am
> > > > > > sure it can be done, just not sure how or where to look
> > > > >
> > > > > If the 10 MHz is visible for a second or two, there is probably a
> > gate to
> > > > > turn it on/off.  If I wanted 10 MHz, I'd open it up and trace the
> > wire
> > > > back.
> > > > > If it goes to a gate, you might be able to lift the pin for the other
> > > > input
> > > > > and wire it hi/low.  There is a good chance it goes to a FPGA where
> > you
> > > > can't
> > > > > get at the gate.
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > These are my opinions.  I hate spam.
> > > > >
> > > > >
> > > > >
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> > >
> > >
> > >
> > > --
> > > Clint.
> > >
> > > *No trees were harmed in the sending of this mail. However, a large
> > number
> > > of electrons were greatly inconvenienced.*
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> 
> 
> 
> -- 
> Clint.
> 
> *No trees were harmed in the sending of this mail. However, a large number
> of electrons were greatly inconvenienced.*
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