Hi. I'm trying to make a system that detects a car with a retroreflector mounted on it passing by. I'm currently using a red laser and a LDR to detect the beam reflected by the retroreflector. The issue is that when the car passes at a higher speed the sensor fails to detect the reflected beam. Should I use a photodiode instead of a LDR for better sensitivity? Or could I change to an IR system? (The system should work outside with daylight, and the car passes about 3 meters away from the device. The max expected speed 100kph) I would really appreciate if you can share your opinion!
Photodiodes are orders of magnitude better than an LDR, in both speed and sensitivity.
Do you think reading directly the analog value from the photodiode will work out? Or do I need some sort of filter to distinguish the LED from sunlight?
Also, the reflected beam diverges quite a bit, is there maybe a way I can focuse it on the sensor (a lense or a tube of some sort)?
All three. To filter out ambient light, most people use a modulated beam (typically 38 kHz) and detect only the modulated component. As in IR remotes.
For amplification of the photodiode signal, use a transimpedance amp (very simple operational amplifier circuit.
With a reflector, just curious… why out it on the car, and not the opposite side of the track?
There could be a situation where two or more cars are passing the sensor at the same time.
Naturally one would need to code for other vehicles to determine which is which, difficult but not impossible.
How did you go with this? I am looking at building a lap timing system using ESPNow and lasers for multiple go-karts. Thinking of putting a reflective strip above the track which will trigger a pick-up as it is reflected. Is this a good approach? Not sure what to use to detect the reflected laser.
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