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### Topic: Sensor for measuring length of an object flying by, and the speed of it. (Read 4422 times)previous topic - next topic

#### jespercm

Hi,
Im quite new in arduino, but good at coding.

For my project i have a chute, where an object passing by, i need a sensor to measure the length of the object (not the distance to the object) and its speed. It has to be quite precisely.

Hope someone know what hardware that could solve my problem.

Regards (:

#### jremington

Describe the dimensions of the chute, a typical object (including the range of sizes) and the range of speeds with which it might be moving.

#### raschemmel

I don't think that is doable. There is no way to know the length without knowing the speed and vice versa. You need to know one or the other. Given the length, you can measure the time it takes to pass by.
If an object travelling at 25 mps takes 0.1 second to pass by , what is the speed ?
If an object travelling at x mps takes 0.1 second to pass by , what is the length ?

#### JimboZA

I don't think that is doable. There is no way to know the length without knowing the speed and vice versa. You need to know one or the other.

I beg to differ....

Leading edge of object breaks beam "A"  at time Ta, then breaks beam "B" at time Tb, calculate time between beams. A and B known distance apart, calculate speed.

Trailing edge of object clears beam "A" at time Ta', we get the speed from previous calc and now we know the time it took for the object to travel its own length, hence calculate length.
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### polymorph

Agreed, as long as the speed isn't changing as it goes by.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8

#### Riva

OP wants to measure both length and speed so it is doable. Problems would be if the object can turn fully/partially sideways in the chute as this will effect length if using beam break timing.
Between what speeds?
Between what lengths?
Between what sizes?
Can they turn in the chute?
Same colours (for possible sensor options)
Don't PM me for help as I will ignore it.

#### robtillaart

jimboZA +1

It's Newton's mechanics.  S = S0 + v*t      v = v0 + a*t     a = a0 + f(t)     // f(t) is often 0;

with 1 sensor you can detect place: S

with 2 sensors you can detect speed: v

with 3 sensors you can detect linear acceleration: a

with 4 sensors you can detect non-linear acceleration:

Note:
above is true as long as the object is not the size of elementary particles, otherwise the Heisenberg principle will affect the measurements. - http://en.memory-alpha.org/wiki/Heisenberg_compensator -
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#### jespercm

i dont have a specific draw of my project, but i quick one, demonstrating the setup:

http://www.tiikoni.com/tis/view/?id=8cb044d

lets assume its a tennis ball running down the chute. Midway on the chute i need somthing to measure speed and the size of the object

i can only use sensors on the front and the 2 sides on the chute, not on the back., Its the same colour, and it will not turn, just slide down the chute.

the object falls by gravity.

What kind of sensor do you have i mind i schould use robtillaart? because then i think i should use 3 sensors, for my measurings.

#### robtillaart

light beam tripwire  e.g. LED and a photo-transistor
when the light signal is interrupted it is detected by the arduino
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#### jespercm

What kind of arduino board would you guys  recomend, for my project:

3 proximity sensors
1 wifi module
maybe 1 lcd display

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