[time-nuts] Fluke Thunderbolt Monitor Revisited

GandalfG8 at aol.com GandalfG8 at aol.com
Sat Jun 5 23:45:39 UTC 2010

In a message dated 05/06/2010 16:18:06 GMT Daylight Time,  
danrae at verizon.net writes:

>  3...The series input and base to ground resistors on the RS232 interface 
> are both 180 ohms, rather than 10K and 3K3 respectively as in  Didier's  
> circuit.
If one  wanted to use the RS232 interface to a computer at the same time 
as the  ko4bb monitor in parallel, which I often do, then you would be 
well  advised to stick to Didier's original values there.  RS232 is quite  
robust, but still...  I built one here quite early on to the original  
design and it has performed flawlessly ever since.

I can not for  the life of me figure out what oriental logic dictated 
these changes in  the first place.
Hi Dan
Many thanks for the comment.
I was going to leave it as is, on the grounds that it worked ok up until  
now, but hadn't taken parallel operation into account and that's something 
I'll  be wanting to do too so will take your advice and revert to the original.
I also tried to figure out the logic for the change but with  similar lack 
of success, and even searched via Google hoping I might  at least find 
evidence of it being done that way before but found nothing.
The last similar circuit I put together was a level shifter for interfacing 
 RS232 to a 3.3 volt supplied Trimble Mini-T and on that I used a pair of  
4K7s with the transistor accepting data from the RS232 port, "normal"  
values do seem to be around 10K each.

And well done Nigel for getting to the  bottom of this!
Much as I'd like to I can't really take the credit for this, it was  Bob 
Mokia after all who alerted Leigh to the fix and I just followed on from  
If I'd taken one apart a few months back as intended, instead of  
dismantling everything in sight for a rebuild, we might have had a quicker  answer, 
but that's the beauty of hindsight for yer:-)
It would also have made life a LOT easier if the board had been designed  
such that it mounted with the component side uppermost.
I'm sure then that somebody would have spotted and resolved  this problem 
ages ago but unfortunately there seems to be an obsession  with concealment 
in some quarters on the assumption that the world and his  granny will rip 
off anything that's not nailed down.
Of course that might be a fair assumption but, given the origins of this  
one, quite ironical too:-)


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