[time-nuts] Fluke Thunderbolt Monitor Revisited
GandalfG8 at aol.com
GandalfG8 at aol.com
Sat Jun 5 19:45:39 EDT 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
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.
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:-)
More information about the time-nuts