linear detuned strobe

tpaddock at tpaddock at
Thu Mar 30 14:28:23 CEST 2000

This is kind of off topic but kind of on topic...

I would like to build a strobe sync circuit to use with 
vibration testing. What I need is an output frequency that 
has a fixed offset frequency from the input. As soon as I 
said that I thought of JH and LINEAR DETUNING.  

How about a F-V converter, add a little offset, 
and then a V-F converter?  The minimum frequency range 
would be about 20-400 Hz and the offset about 1.5 Hz. 
The offset frequency is not critical, but it would be nice 
if it was adjustable 1-2 Hz. I don't think I'm explaining 
this very well.

For instance:
shaker freq= 20Hz, strobe freq= 21.5Hz
shaker freq= 400Hz, strobe freq= 401.5Hz

Any good V-F and F-V chips to recommend? Or a better way?

When you look at something vibrating with a *detuned* strobe, 
it looks like it is in slow motion. Wires wave (reminds me of 
hula dancing), big components rock on their wires, transformer 
windings wiggle on their cores, PWBs flex and  mechanical 
engineers get a haunted look in their eyes. The frequency is 
being swept, typically at about 1 octave/minute, so you can't 
set the strobe frequency by hand.  

By the way, if you look at your hand while you hold it on the 
shaker table, you can see the skin and meat *undulating*. 
It would make a great special effect.

 - -- -  Toby Paddock
Three Faces of Odyssey

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