They show you how to make speed gun at EPE when i find it i'll post what month it was in

For an object traveling through air the rise time of the photo transistor is effectively irrelevant, you just need to measure the exact moment when the signal hit's it's peak, if both sensors are the same then you measure the distance between the two peaks and you're all set. Not sure how you would interface this to a sound card, but if the projectile is small and you simple feed the transitor output into an or gate you'll see ticks on the sounds wave form corresponding to the interuption occuring and then ending. OR'ing both inputs together and you should see the two peaks you need to measure the distance. At 44.1khz you count the number of samples between peaks, multiply by the reciprocal of 44.1 khz and you have a very accurate time stamp. If you have really slow photo transistors increasing the distance between the two points to perhaps 5 feet will help separate the two peaks. Should be pretty easy to test.

The link you posted says how the author thinks it should be interfaced with a sound card, and mentions that a link will be provided next week for the circuit to do so. He also provided no details about the photo transistor or how he determined the rise time was too slow.

All you need to do to remove the rise time of the sensors from the picture is to increase the distance between the sensors so you can determine the two individual peaks.

Conversion from .hex to .asm is bad enough from .hex to C code would be completely unreadable. Contact the author and request the original form of the code then you have something decent to go with.

Originally Posted by MrDEB

is ns faster than us?

Too basic to be asked. You should be able to answer that question after searching and reading about units.

Have you tried?