[time-nuts] A real-world precision timing need....
mpb45 at clanbaker.org
Sun Oct 31 12:56:17 UTC 2010
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
Gainesville, Florida, USA
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