Re: digital oscilloscope, dispersion, TI-86, etc, etc...

[gastineau@badgerden.com (John E. Gastineau)]

You can do all the experiments I described (FFT of a paper towel tube 
"thunk", beats, reflections from a packing tube end) using Vernier's 
Sound software. Sound costs $30 for a site license, and is currently 
available for DOS and Macintosh. Sound requires a ULI and a 
microphone, and has a maximum sampling rate of about 11,000Hz, which 
is plenty high for these experiments. 

Since I haven't used digital oscilloscope, I can't say what the 
advantages are of that package. I have been teaching using Sound for 
years, and it works well. The FFT function is invaluable. 

Some of you may have CBL units with a microphone. You can do the 
beats experiment just fine, but the FFT experiment is tough. You just 
can't acquire enough points to do the FFT well, even if you had the 
FFT software. The packing tube reflection experiment might work, but 
you'd have to trigger VERY carefully since the CBL can only acquire a 
limited number of points. With the TI-82 you can only collect 99 
points. With the 83 you can get more, but are limited to maybe 300 
points due to memory constraints. The new TI-86 calculator has 4X 
the memory of the older models, so there's a good chance that you can 
do the reflection experiment. You'd still be limited to 512 points 
due to limitations of the CBL itself. I will try the experiment on an 
86 later this week. (All my stuff is packed up right now for a 
workshop.)

Another fun demo can't be done with Sound, but can be done with a 
package called MacRecorder, among others. (At least that's what I 
think it was called. When you switch institutions you loose 
things...) The experiment is this: Take a slinky and make a tin-can 
telephone with it (like with a string but using the slinky). You can 
buy commercial versions of this at toy stores. Now tap one end of the 
device,  sending a pulse down the system. The  slinky demonstrates 
dispersion very nicely. By the time the tap, basically a square 
pulse, makes it down to the other end the many frequencies contained 
will have been dispersed in time. At the listening end you'll  hear a 
swooping sound reminiscent of certain Star Wars light sabre sound 
effects. Now, the computer part. Record the sound digitally, isolate 
it so you have just the swoop, and then play it back backwards. Play 
the reversed sound into the slinky telephone,  and listen at the 
other end. You will hear a very satisfying click, corresponding to 
the time-compressed swoop, ie, the original tap. 

This experiment is an acoustic analog of a laser pulse-shortening 
technique using a chirped laser pulse. By using an appropriate 
dispersive medium, the pulse can be temporally narrowed to sub-pico 
second lengths. I do this demo for laser and optics courses.


On 19 Jan 97 at 15:10, kowalskil@alpha.montclair.edu wrote:

> Raymond A. Rogoway wrote about his Digital Oscilloscope (see below).
> Is it true that having an ULI I do not need "Digital Oscilloscope"?
> Can all John's demos be performed with Vernier's "Sound" for
> Macintosh? What is the highest sampling rate of Sound? What are real
> advantages of using Digital Oscilloscope?
>                                                     Ludwik Kowalski
> *******************************************************************
> > Digital Oscilloscope cannot be used with the ULI. It is self
> contained. > It can operate with the internal mic on the Mac and
> even has a feed-through > so that you can hear to sounds. You can
> adjust the triggering point or let > it free run, just as a normal
> oscilloscope. It also has a frequency meter > mode in which a
> frequency meter (counter) is displayed in large numbers > instead of
> the oscilloscope. What it lacks that the Vernier stuff has is > a
> fast fourier transform feature. The Vernier ULI uses a software
> package > called "Sound" in which you can have multiple screens,
> triggering, and a > FFT function, along with curve fitting. The
> software is cheap.

--
John E. Gastineau
900 B Ridgeway Ave.
Morgantown, WV 26505
(304) 296-1966
http://www.badgerden.com/~gastineau
gastineau@badgerden.com