[time-nuts] A real-world precision timing need....

Michael Baker mpb45 at clanbaker.org
Sun Oct 31 12:56:17 UTC 2010

   Hello, Time-Nutters--
   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
   shooting bench.
   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!!
   Mike Baker
   Gainesville, Florida, USA

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