I made a design of this small equipment for measuring the speed of the spear gun shaft underwater. It is supposed to measure speed on any distance from the gun, along path of about 10 cm for which time should be calculated from the voltage shown on DVM before and after shoot. 220 uF capacitor discharges though 10 Ohm resistor. This might be OK for shaft speed from 35 m/s to 5 m/s.
[ame="http://www.youtube.com/watch?v=q-nprjzlS4A"]YouTube - Brzinomjer[/ame]
DVM will be in PVC bag connected to the housing of equipment.
From the above demonstration the time is t1-t0 = ln(810/646)*0,000220*10 = 0,498 ms and the speed is 31,14 m/s because the length is 0,016 m.
[ame="http://www.youtube.com/watch?v=q-nprjzlS4A"]YouTube - Brzinomjer[/ame]
DVM will be in PVC bag connected to the housing of equipment.
From the above demonstration the time is t1-t0 = ln(810/646)*0,000220*10 = 0,498 ms and the speed is 31,14 m/s because the length is 0,016 m.
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