[time-nuts] Subject: Re: Working with SMT parts (Bob Albert)

[Jim Stone]

Hi again,
The cable impedance measurement was in a different video (linked below) but
it can use the same HC14 TDR as in the first video. The concept is to just
put a pot on the end of the cable and adjust it until the reflection goes
away. Simple!

https://www.youtube.com/watch?v=Il_eju4D_TM

--Jim Stone


Hi Bob,
Take a look at this nice simple little one chip "TDR" and lesson on how to
use it to measure cable length and cable impedance. It uses a single AC14
(can use a DIP so no SMD needed) and gives a nice crisp 2 or 3 ns rise. The
AC family is nice fast logic and has been used in many Time-Nuts
application like cheap zero-cross detectors using the AC04.

https://www.youtube.com/watch?v=9cP6w2odGUc

Regards --Jim Stone

Bob Albert wrote:

 Well I got my adapter boards from China and managed to build my first SMT
project, a square wave generator for TDR use.  And it works!  The IC seems
to run hot so I used my IR temperature measurement device and it checks out
at about 37C, acceptable.  I can now drive a square wave at about 3 kHz
into 50 Ohms.  The rise time isn't very short but I must have not used the
best part for the generator.  Still, I can do some TDR experimenting as
long as the line isn't too short.
Thanks to all for the ideas and encouragement.  I didn't use a microscope,
mostly just a magnifier.  My tiniest soldering iron is a bit large but it
did the job.
Bob