I need to measure the time at which a arrow flies 70m, so I need to create two sensors that can detect when the arrow, with a diameter of approximately 5mm, crosses the plane. The area size is 1.2x1.2m. A vertically expanded laser beam (like a construction level) could be used as the transmitter. For detection, photodiodes could be used, but that would require many of them, and perhaps there are other methods to detect the crossing of the plane. Preferably optical sensors, as they have higher accuracy. Any suggestions on how to create or improve this? (google translate)
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Maybe some version of this.
Obviously the two detectors would be 70M apart. -
You might try to see if the schematics are on the internet.
Would such a detector be accurate if its size were increased to 1.2x1.2m? This is cheap, but not very accurate.
Hi, @mail303
Welcome to the forum.
Any reason for 70m distance?
Are you measuring time of flight or arrow speed?
Thanks.. Tom.. 
Not necesssarily. Commercial scanners, in my experience, use only one detector. Referring to the image below a detector mounted coaxially with the outgoing (visible) laser beam responds to the beam reflected back into the device. Varying light/dark areas will cause the detector output to be modulated accordingly. These are then converted into digital signals and thence interpreted as a bar code, for instance.
To detect a single dark area would be relatively much simpler. A curved 'target' mounted a known distance from the laser reflects the beam, similar to the chrono sensors pictured in post #2. This is just an overview - lots more involved in practice. If you could lay hands on a basic scanner it may be possible to sense an arrow passage and add a timestamp.
Note - the speed of the rotating mirror is many times faster than that shown.
time of flight
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