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Hi, I'm very new to the Arduino Community and I have almost no coding experience.

For my science project, I have to measure the velocity of an object (projectile).

I was going to use a laser and a photoresistor to measure the time. (Since I will know the distance between two laser beams I will be able to calculate the velocity.) However after my research on the web, I have discovered that using this method will be too slow or inaccurate. Another way of measure time I discovered was very accurate but it was using: circuit breaking method. (using a tin foil to create a circuit and the projectile breaks it when it passes trough)

I need a non-destructive way to measure the velocity. If, using a laser and a photoresistor can't do it what will be the alternative? (I'm thinking of IR...)

I will be using Arduino Uno R3 for this project, and LCD to display the velocity.

Projectile details:
Size: Around table tennis ball
Velocity: Less than 3m/s
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I don't think you connected the grounds, Dave.
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However after my research on the web, I have discovered that using this method will be too slow or inaccurate
[citation required]
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I got that information from:
http://arduino.cc/forum/index.php/topic,114435.0.html

But, if the projectile is moving at less than 3m/s, I think it might work...
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I certainly wouldn't use a photoresistor (LDR) for high speed stuff, but as far as I know, commercial ballistic chronographs use photodiodes.
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You could use either photodiodes/phototransistors. Doesn't necessarily have to be IR, though. The reason for IR is that you can filter out visible light, and not have to worry as much about whether you're going to use it on a sunny day or in a dark closet, and having your bright/dark transition level moving around. You will probably still need to have an external analog circuit and a potentiometer to adjust the transition level, but using IR instead of visible light will make the dynamic range much lower.
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I saw a tutorial (at hackaday.com or so), where a guy was building exactly what you want to build.
He drilled 4 holes in a pvc-pipe and placed ir-leds and phototransistors in the holes, so he could measure the light difference when the round runs through the pipe. Seemed to work pretty good.
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