Analog trigger with raster scan

[slimbim]

I have two saw tooth analog inputs. These saw tooth waves create the vertical and horizontal rasters for a scanning device like a TV or scanning electron microscope or a scanning tunneling microscope. I am trying to acquire an image using the saw tooth waves as analog triggers and then acquiring data on another channel. I have written a simulation vi This uses the "Trigger and Date" vi to detect when the sawtooth suddebly flicks back. The first frame waits until the y scan has flicked back to the top, then the next frame starts a timed acquisition for each horizontal sweep. At present an artificial image is created. I am having problems with the triggering side of things when I try to convert this vi to work with real signals. I imag
ined I could just replace the "Simulate Signal" vi with my real sawtooth input, but this does not appear to work. Does anybody have some suggestions?
Many thanks
Chris Walker

[chutla]

Dear Slimbim:

At what point on the flyback are you triggering your acqusition? Depending on how steep the slope is on your sawtooth, you may need to build some kind of comparator, such as one that triggers when it drops to 50% of its amplitude, or some such. I imagine your electron microscope akready has a "real" trigger output available. I'd check the documentation on that first. Also, take a good look at your sawtooth with a wide-bandwidth scope....you might find the rise (or rather fall) time of your flyback isn't all that great! You might need to build a schmitt trigger to speed things up a bit, if you're undaunted by external hardware!

Just a few suggestions..

Eric