[sdiy] trying to get my scope to see CHAOS??

[Dave Manley]

Dan Snazelle wrote:
> this is mainly a question I think Ian (the creator of the module I am using right now) might be able to answer, BUT just on the chance somebody else is checking the list at this hour, i figured i'd throw it out here. 
>
> I REALLY want to get the kind of results from the jerkster that ian is getting in these scope shots:
>
> http://home.comcast.net/~ijfritz/ch_cir2.htm
>
>
> SO...i connected X to channel A of my scope. And Y to channel B.
>
> I put my scope in the right mode....all i get is a square, or a dot that moves in an very strange trace...like it is slowly drawing something out with the dot...sometimes a loop. i wonder if Ian has a special scope that allows the path of the dot to STAY on the screen as it traces out the weird shape?
>   
If the dot is slowly drawing something, it sounds like everything is 
working properly, but the chaotic input signals are just changing slowly.

Put the scope into normal sweep mode, and look at either signal.  How 
slowly are they changing?  Adjust the rate of the Jerkster's outputs so 
that it is oscillating (or more correctly, chaotically varying) 
quickly.  I don't know what the max rate at which the Jerkster will 
'oscillate'. Set the gain on each input channel so that the signal 
amplitude fills the screen.  Then switch back to XY mode.  Does it look 
better?  You may need to play with the gain and offset for each channel 
to center the figure.  This may not be the way you want to use the 
circuit for audio/synth use, but is better for pretty XY-mode pictures.  
You want the time for the circuit to complete an 'orbit' to be fast with 
regard to the persistence of the scope, or another method would be to 
use a camera with a long exposure time.

Also, to answer your other question, some scopes have an 'infinite 
persistence' mode where the trace doesn't fade until you clear it.  This 
mode works better on modern digital scopes than it ever did even on the 
best, old Tektronix analog scopes.

-Dave