[time-nuts] GPS for Nixie Clock

Bob Camp kb8tq at n1k.org
Sat Jul 16 11:04:22 EDT 2016


Since we have moved into synchronizing this stuff at the nanosecond level 
(maybe we are even lower than that by now ..), simply getting a wide band
enough signal off of a Nixe socket is going to be “interesting”. An array of picosecond
photo diodes on each tube may be the only way to go. How many channels 
this all will take depends a bit on how many digits past the second the display
will show. Is it 9 digits past the second? 

Since you will only know the ignition point *after* it has happened, the system
only works to a certain degree. Trigger point *is* dependent on the light level. 
You will need to collect real time data to keep things consistent. 


> On Jul 16, 2016, at 10:49 AM, David <davidwhess at gmail.com> wrote:
> Use AC coupling to each digit to measure the ignition waveform and
> detect the breakdown point like with a tunnel diode trigger.  Use a
> higher compliance voltage and greater negative resistance (constant
> current drive?) to lower breakdown jitter.
> On Sat, 16 Jul 2016 00:08:45 -0700, you wrote:
>> Yes, I was planning on using a high speed photo diode to actually 
>> measure the turn on time of the digits. I hadn't thought of the turn OFF 
>> time, do I want the old digit to be turned off before the new one lights 
>> up or for them to be overlapping? I have been thinking about what 
>> threshold to use, 50% intensity is probably about as good as any other. 
>> It might turn out that different digits turn on differently, so I will 
>> have to calibrate each one separately.
>> John S.
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