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Ballistics board.
I am working on a ballistics board for The AGROVATOR pumpkin cannon.
agrovator.com
We have the tilt of the barrel controlled with an air motor. The XY axis is on a bearing from a tank turret. Even though it weighs a few thousand pounds, it is easy to move around.
I am working on a chronograph, and I have designed a potentiometer with a weight for the angle of the barrel measurement.
The barrel is 9 inches in diameter, so for the chronograph I  am using LEDs and phototransistors.
The leds didn't werent bright enough at 12 inches apart.
In order to get the leds to be brightest without burning up I I drove the leds with PWM (instead of a resistor) and got the PWM port to read @ 4 volts with my meter. which is double of what the LED can handle.To keep it from burning up I turned it on and off at 6 milisec intervals.
Its not perfect but its an ok start.
With velocity and angle I should be able to get a good guess at distance.

Does anyone have any experience with pressure sensors that can handle abuse?
Is anyone else working on ballistics?

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Greenville, IL
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Does anyone have any experience with pressure sensors that can handle abuse?

  How much pressure are you talking? Do you want a exact measurement or a switch response when pressure has gotten high enough?
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Are you using analogRead() or digitalRead() with the phototransistor? If digitalRead() then that would explain why you're having problems getting them to register as "on".

Typically in your setup() you would write your program to take analog readings from the phototransistor when the LEDs are off then when they are on, then set a threshold somewhere between the two readings as to trigger when your pumpkin is blowing past.

The CameraAxe uses infrared sensors in a manner you're describing to set a camera to trigger when an object is moving past. It's certainly a doable project.
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We shoot pumpkins @ 60 psi, the tank is rated for 150 psi.
60 psi = @ 3000 feet of range
what happens is anything beyond the acceleration that is caused by @ 80 psi chunks.
I will get Analog pressure sensors  when I can find them cheap enough, 
I found a pressure activated switch, it looks like there is a set pressure and when the measured pressure falls below or rises above it, it triggers the switch. It seems like reed switches are going to0 be  slow.
for the chronograph, I used analog write to drive the led, when it is installed there will be 30 feet of wire going to it (at the end of the barrel)(voltage drop) It was easier to tweak the voltage of the led with analog write, than using regulated voltage and a resistor. The photoresistor  is into an analog port with a  resistor to ground.
I set a threshold by averaging 3 inputs and dividing that number by 2 to trigger a timer (for statement).
It is constantly tweaking the threshold depending on the current light conditions.
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  These sensors may be above your price target http://search.digikey.com/scripts/dksearch/dksus.dll
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thanks,
Ifound the Honeywell NSC seems to fit the bill.
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@welder dan
Do you have some pictures/video's? sounds like an impressive project ...
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thanks for your interest.
We dont spend alot of time on marketing.
this video is from the big ten inch world record holders website. there is a pan view of the agrovator, (2010)

there are links on our site to the photo albums.
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