[Spork] over on the Netduino forums wanted to push the limits of what his little board could do. He put together a chronometer to measure the velocity of rifle rounds and Nerf darts using an Arduino-compatable CPLD shield.
The project is built around a pair of commercial CED M2 chronograph sensors; because people have the tendency to shoot through these sensors, they’re available as replacement units for much less than the cost of a complete chronograph setup. [Spork] couldn’t figure out a way for his Arduino clone to read pins with a resolution of 1 microsecond, so a Amani GTX CLPD shield was added to the build. This programmable logic chip takes the output from a chronometer sensor, starts a timer, waits for the second sensor to trigger, and stops the timer. From that, the velocity of just about any projectile can be calculated.
Of course, [Spork] needed to test his new device, so he took it out to the range and fired 25 rifle rounds through his chronometer. The result was a very nice, normal distribution centered around 2400 feet per second, exactly as would be expected. Although [Spork] didn’t test out low-velocity projectiles such as Nerf darts, we expect the same reliable results.