A cheap beam break sensor utilising a reflector panel instead of a transmitter / receiver setup. Capable of handling long distances.
Project tutorial by mova
We haven't had snow or fog just yet. I'm even unsure if it rained yet. But it's a valid concern. I experienced that just holding my black glove in front of the sensor (20-30cm) was reflective enough for the receiver.
I also considered a laser and actually bought some IR lasers but went LED because of several reasons.
1: I didn't want to burn my own or any others' retinas. The sensor is mounted where someone might be tempted to take a peak inside the tubing.
2: Aiming of the laser is difficult and it must be pointed directly at the retroreflector.
3: When testing a red laser on the reflector panel I discovered one possible disadvantage of lasers. The laser beam is wide enough to cover several of the reflective "corners" that the reflector panel consists of. The result of this is that it is not one but several "beams" that get reflected back to the sensor. If not the receiver part is directly in the path of one of these beams no light will get to it. With LEDs this was not an issue.
Imagine holding an LED flashlight right next to a wall, pointing it away from the wall. Then when putting a retroreflector in front of the beam the wall around the flashlight will light up nice and evenly, even if you move and rotate the reflector slightly.
When holding a laser instead the reflected light on the wall will be a pattern of dots and this pattern will move a lot with the slightest movement of the reflector panel. I didn't test it but I'm guessing it would be a pain to align the laser correctly and have the sensor not respond to these movements
On a side note, traffic reflectors aren't necessarily perfect retroreflectors. They're designed to return the light not directly to the source but slightly off so that you can see the pedestrian/bike from inside the car even though the light shining on him comes from the front of the car or maybe from another car that actually remembered to switch on their lights...
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