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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Even 10cm won't give great accuracy... If you assume that the sensors are accurate to +/- 2mm, that gives you almost a +/- 5% error. That would make fine tuning quite tricky, you would have to run several trials and average to see an small trends.
Although I guess if you are using a 10cm projectile the system is so out of tune it probably doesn't matter
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
yes, my projectiles are shorter than the distance between the photogates. i wired two photogates in 10cm distance, the first one goes to a inverter, then to the set input of an RS flipflop,a nand gate switches the 1mhz clock signal to the counter. when the projectile passes the second photogate the output goes to an inverter, then to the reset input of the RS flipflop, the counting stops. cause the clock signal is 1mhz, you just have to calculate 100000 / measured time and you get m/s
heres a pic of my prototype ,
very crappy but it works. yesterday i finished the final pcb in eagle, maybe someone is interested
its not tested yet but i think it will work, its almost the same as my prototype.
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How to control a counter with separate start and stop pulses?
