The two simplest ways are optical and microwave. Optical is cheap and
simple. Microwave is a bit more expensive , but also reasonably simple.
The best method for optical, assuming you are using this for test
firing, and not 'live', is to use a dark box or tube with a pair of
linear sensors placed about 1m apart, depending upon needs/space etc.
Illuminate these with a collimated laser set to give an elongated beam
aligned along the sensor array. Configure the sensors at each end in an
OR arrangement such that any sensor losing the signal causes a pulse
output. Then simply measure the two edges using a micro. The faster the
micro the better the resolution, and more accurate the measurement. With
a muzzle velocity of 1600m/s and a spacing of 1m the time between pulses
will be 625usecs. An 8MHz clock would give you 5000 clock pulses. 4999
clocks would be equivalent to 1600.32m/s, while 5001 would be 1599.68.
Alternatively 24GHz DROs can be had quite cheaply, and a 26dB gain horn
is reasonably simple to construct. simply align the DCO and its
recording circuitry alongside the muzzle, and aimed in the same
direction. The doppler frequency gives the velocity quite accurately.
Thsi has the added advantage of being useful for 'live' firing. You
might even get away with one of the cheap 10GHz DROs with patch antennas.
Al
