[time-nuts] FE-5680A ("New" version) fine frequency adjust

[Don Latham]

Let me add my thanks. My knowledge of FPGA's is about the same as my
knowledge of the female of our species. Is it possible to read the
program that's been entered into the chip? I'm not clear as to the data
flow in this beast. If the control loop is indeed digital, then there's
a PID controller in software? It's possible then to control the
frequency as some want to do with the beast as it is, using an Arduino
or Picaxe or some such to adjust the frequency with an external loop and
digital corrections via the rs232 rather than all this crude analog
resistor stuff :-)
Don


EWKehren at aol.com
> Pete
> Thank you, I will look at its some time in the future, right now I let
> it
> cook for a couple of weeks undisturbed and than I may cut the trace that
> seems  not to do any thing. If you have a 100 MHz scope it will trigger
> on any
> pulse in  this unit unless your scope is defective. I think there are
> features hardware  wise in this unit that can be activated at
> manufacturing
> depending on price and  demand. I am sure you are aware of instruments
> that a
> hardware wise the same and  cost any where from $15 000 to $40 000 the
> only
> difference is the software  imbedded and many times you can buy an
> upgrade.
> Bert
>
>  message dated 11/18/2011 10:26:02 A.M. Eastern Standard Time,
> bell.peter at gmail.com writes:
>
> All the  pins have things connected to them - but pin 6 seems a little
> strange -  it's connected to the 'ACT240 (in fact, it goes through 3
> sections of the  chip in series!) and finally to the xilinx chip - but
> none of these signals  ever appear to do anything and the output is
> just constant high.  It's  possible that this the pulse is just
> extremely short - the fastest scope I  have at home is only 100Mhz -
> but I would have expected to be able to  tirgger on it at least.
>
> Regards,
>
> Pete
>
>
> On Fri, Nov 18,  2011 at 9:09 PM,  <EWKehren at aol.com> wrote:
>> Pete
>>  Thank you for doing all the work. This is great info and will help
>> all
> of
>> us that want to discipline the beast. One more question, since you
>> have
> done
>> so  much testing is there one pin on the connector that  has nothing
>> connected to  it?
>> Thanks again   Bert  Kehren
>>
>>
>> In a message dated 11/17/2011 9:59:14 P.M.  Eastern Standard Time,
>> bell.peter at gmail.com writes:
>>
>>  OK, I  just managed to get some spare time to have a look at this,
>> and
>> here are  some conclusions:
>>
>> 1) The fine  frequency adjust pot is not connected to  the c-field
>> circuit.  All the connections to it go across the board to the
>> MAX1246
>> ADC  chip.  The track is wired between ground and the vref  output  on
>> this chip and the wiper goes to a little pi filter (ceramic cap,
>> 100K,
>> 1uF tant) that feeds channel 1 (pin 3) on the ADC.  As far as I  can
>> see, it goes nowhere else.
>> 2) The  c-field current is fixed.   The circuit is very simple - there
>> is  a 5.1V reference generated using a  zener and a 681R resistor to
>> the
>> 8.8V and this is fed into a potential  divider consisting of  a pair
>> of
>> 120K resistors.  The centerpoint of  this divider  is connected to pin
>> 5
>> (+ve input) of a TLC27M4BI - the output  of  this amp (pin 7) is
>> connected via a 270R resistor to pin 2 of the FPC  connector and hence
>> to the c-field coil.  The return side  of the coil  (pin 1 on the FPC
>> connector) connects to pin 6 (-ve)  of the opamp and via a  620R
>> resistor to the 5.1V  reference.
>>
>> If there is any other input to  this circuit,  I have not been able to
>> find it, despite probing all over the  board.
>>
>> Conclusion:
>>
>> This version carried  out the fine frequency  adjust digitally by
>> changing the reload  values on the DDS chip - the reason  the pot does
>> does nothing in  this specific model is that the DDS trim is  now
>> being
>> carried  out over the RS-232 port and as a result the pot value  (if
>> it's  being read at all) is not being used for  anything.
>>
>>  Adjusting the c-field still works, though - if you connect a  DC
>> supply
>> set at about 2.55V via a high value resistor (I used 100K) to  pin  5
>> on
>> the TLC27M4BI next to the flex cable connector then you  can trim  the
>> frequency by adjusting  it.
>>
>>  Regards,
>>
>> Pete
>>
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-- 
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
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www.lightningforensics.com
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