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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 from: AWOL on August 14, 2013, 02:58:34 amQuoteDo you think this Miniature Solar Cell - BPW34 will do the trick?No, I don't think it'll be fast enoughOh... 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 Quote from: AWOL on August 13, 2013, 07:01:23 amUse a photodiode or phototransistor.Do you think this Miniature Solar Cell - BPW34 will do the trick?https://www.sparkfun.com/products/9541Datasheet: 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 Quote from: CrossRoads on August 12, 2013, 12:04:36 amPhotoresistor 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 cmt = 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 from: AWOL on August 12, 2013, 02:32:25 amQuote of measuring a projectile traveling at around 350 to 400 m/sMach 1+ ping-pong balls?Some serious over-estimation there, I think.It is a 2 meters long vacuum cannon.P = Atmospherics pressure = 101325 Pascalr = 0.02 meters A = (pi)(r)^2F = PAF = (101325)(3.14 X 0.04) = 12732.8750W = Fd = (12732.8750)(2) =  25465.75W = (1/2)(m)(V)^2V = square root((2 X 25465.75)/0.04) = 1128V = 1128 m/sConsidering energy loss, we are just assuming it to be around 350 m/s to 400 m/sso 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/sI 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.htmlPlease 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...  (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 LeonardoHere 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... 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.htmlBut, 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 ballVelocity: Less than 3m/s
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