[time-nuts] HP5065A digital clock info

ed breya eb at telight.com
Wed Sep 28 19:04:32 UTC 2011

Yes Bert, the "three-board" type uses the counting scheme that you 
described, but the other type is as I described. On the "two-board" 
version the "set" mode is permanent, and there is no external counter 
or logic. The 555 is a normally a one-shot for stretching the narrow 
1 PPS pulses from the Rb system, but oscillates at around 60 or 600 
Hz (precision not important) during setting, accomplishing the same 
result. I think this design is the later one - someone at HP may have 
had a "eureka" moment and realized that this simpler approach could 
eliminate a board full of logic.


In a message dated 9/27/2011 9:10:25 P.M. Eastern Standard Time,
<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>EWKehren at 
aol.com writes:

Sorry  Ed  you are wrong. Hp generates a 65 Hz signal that advances the
internal prescaler 49 counts and uses the 1 pps output to stop the 65  Hz
output at count 49 and waits for the internal 1 pps to go to 50  and
advance the
second digit one count. Sounds crazy but it works,  makes the clock advance
in  perfect sync with the internal second  generator.
Bert Kehren

In a message dated 9/27/2011 8:16:43 P.M.  Eastern Standard Time,
<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>eb at 
telight.com writes:

After looking at the manual, I  realized that I  did look at this
series of parts way back, but  didn't get the connection  because I
thought it would have to be a  type that takes 1 Hz input rather  than
50/60 Hz. I see now that they  were used in the "set" mode, bypassing
the internal divide by  50/60.

The clock module I have is the type  with a 555 used as a  one-shot for
normal operation, or as an oscillator  for fast setting.  I think this
is probably the newer of the designs, since  it is  simpler.

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