[time-nuts] PICTIC II ready-made?

[EWKehren at aol.com]

Has any one considered asking Richard. As far as logic is concerned a 200  
MHz Altera MAX 3000A makes a perfect substitute at a cost of $ 2.50  that 
includes a very solderable socket. Works
Bert Kehren  
 
 
In a message dated 4/25/2012 3:16:51 P.M. Eastern Daylight Time,  
bruce.griffiths at xtra.co.nz writes:

Chris  Albertson wrote:
> On Wed, Apr 25, 2012 at 9:37 AM, Don  Latham<djl at montana.com>  wrote:
>
>     
>> I forgot to add that a simple redrafting of the II as an Arduino  shield
>> with appropriate chips and chip passives would accomplish  the desired
>> end without losing the very careful engineering and  testing that has
>> already been done?
>> Would be nice to  have a way to change caps without soldering as well,
>> maybe just  some .1" jumpers?
>>      
>
> Yes, MOST  of the design could be re-used.  As an Arduino shield there is 
no
>  need for a PIC or RS-232 interface becusethe Arduino does that  function.
>   You'd need to replace the 74ACT175 part but that  is not hard.
>
> About changing the cap values without  soldering.  I guess you could push
> the leads into a 0.1 inch  header strip or install several and use a DIP
> switch to select which  are "in".   But I don't know if the extra 
inductance
> al that  wiring adds is enough to worry about.
>
>    
The  time to digital converter (TDC) section is merely an interpolator 
that  measures the delay of a synchroniser.
The TDC range should be about 2 clock  periods to accommodate the range 
of synchroniser delays and to facilitate  calibration.
Unless one is changing the synchroniser clock period there is  no need to 
vary the TDC gain.
The SR620 uses a similar interpolator and  has only a single interpolator 
range.
The range is extended by counting  the number of synchroniser clock 
periods between synchroniser output  transitions of interest.
When measuring the time interval between 2 signals  a pair of 
synchronisers and interpolators are used.

Interpolator  nonlinearity can be measured by using a statistical fill 
the buckets  technique which uses nothing but a pair of noisy 
asynchronous oscillators  with high reverse isolation to avoid injection 
locking.

If a  suitable ADC is used the interpolator can be simplified 
considerably  whilst improving its performance.
Minor nonlinearities are of little  significance, as long as they are 
repeatable and relatively stable they  can be easily corrected in  software.

Bruce

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