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1  Topics / Science and Measurement / Re: Measuring the speed of a projectile on: August 14, 2013, 05:47:13 am
Quote
Do you think this Miniature Solar Cell - BPW34 will do the trick?
No, I don't think it'll be fast enough

Oh... I don't know what device to use now...
2  Topics / Science and Measurement / Re: Measuring the speed of a projectile on: August 14, 2013, 02:47:23 am
Use a photodiode or phototransistor.

Do you think this Miniature Solar Cell - BPW34 will do the trick?
https://www.sparkfun.com/products/9541

Datasheet:
https://www.sparkfun.com/datasheets/Prototyping/Solar/bpw34.pdf
3  Topics / Science and Measurement / Re: Measuring the speed of a projectile on: August 13, 2013, 06:56:48 am
Photoresistor would be fine -  you have the same delay in detecting at two points, so they cancel out.
interval time = (T2+time_delay) - (T1+time_delay) = T2 +time_delay - T1 - time_delay = T2 - T1.
Also has the benefit of no tin foil impacting the time by slowing down the ball at all.

I am just worried because I have never used a photoresistor for anything... and the projectile is moving very fast...
Also the photoresistor I have is a crap one (I believe) that just came with SparkFun Arduino starter kit...

Edit:
Based on simple calculation
Assuming it is traveling it at 350 m/s, a large projectile (cylinder shape with hemispheric nose and tail) which is around 6 cm
t = d/v = 0.06/350 = 0.0001714 seconds...
Arduino has 16 million clock cycle which is plenty to get readings but I think the photoresistor is just not that responsive...
4  Topics / Science and Measurement / Re: Measuring the speed of a projectile on: August 13, 2013, 06:48:54 am
Quote
of measuring a projectile traveling at around 350 to 400 m/s
Mach 1+ ping-pong balls?

Some serious over-estimation there, I think.

It is a 2 meters long vacuum cannon.
P = Atmospherics pressure = 101325 Pascal
r = 0.02 meters
A = (pi)(r)^2

F = PA
F = (101325)(3.14 X 0.04) = 12732.8750
W = Fd = (12732.8750)(2) =  25465.75
W = (1/2)(m)(V)^2

V = square root((2 X 25465.75)/0.04) = 1128
V = 1128 m/s

Considering energy loss, we are just assuming it to be around 350 m/s to 400 m/s
so around 780 mph to 895 mph
5  Topics / Science and Measurement / Measuring the speed of a projectile on: August 11, 2013, 11:28:45 pm
My school has a vacuum cannon and it fires small table tennis balls. We can only calculate the velocity theoretically because my school does not have any device that is capable of measuring a projectile traveling at around 350 to 400 m/s

I was thinking of using two tin foils and measuring the time interval of opening circuit. (Using a photo resistor would be too slow)
I did some research and I did find some useful resource: http://forum.arduino.cc/index.php/topic,114435.0.html


Please give me some advice on how I should tackle this problem. (Should I just use the method I found?)
6  Using Arduino / Programming Questions / Re: Arduino Leonardo error on: October 21, 2012, 01:52:26 am
Still comes up with that same error...  smiley-sad (I've tried many different USB ports on my laptop...)
7  Using Arduino / Programming Questions / Arduino Leonardo error on: October 20, 2012, 09:46:13 pm
I got my Arduino Leonardo connected to my computer for the first time and it's coming up with an error...

I ignored the error and used the Arduino compiler to upload the code to the Leonardo

Here is the code:
Code:
void setup()
{
  pinMode(2, INPUT);
  digitalWrite(2,HIGH);
  
  Keyboard.begin();
  
  while(digitalRead(2))
  {
  }
  
  Keyboard.println("Arduino Leo Keyboard function test");
  delay(1000);
  Keyboard.println("Test version 1.0.1");
  delay(1000);
  Keyboard.write(48); // character 0
  delay(2500);
  Keyboard.press(KEY_BACKSPACE);
  delay(1000);
  Keyboard.releaseAll();
  
}

void loop()
{
}
 

When I try to upload, an error message pops up: "Couldn't find a Leonardo on the selected port. Check that you have the correct port selected. If it is correct, try pressing the board's rest button after initiating the upload." (There is a reset button but it doesn't seem to work... smiley-roll-sweat or I'm not using it right)

When I click "Serial Port Monitor" on "Tools" bar, again an error message pops up: "Serial port 'COM6' not found. Did you select the right one from the Tools > Serial Port Menu?"


Questions:
1. How do I rest the Arduino Leonardo board?
2. How do I upload any code to Arduino Leonardo board?
8  Topics / Science and Measurement / Re: Measuring the velocity on: September 14, 2012, 03:11:35 am
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...
9  Topics / Science and Measurement / Measuring the velocity on: September 14, 2012, 01:54:13 am
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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