Ultrasonic Sensor as Start/Stop signal

I want to use this Ultrasonic Sensor THIS to create a LapTimer for my RC Car.

I tried several things with IR LEDs, but this requires a setting on both sides of the track, I don't want that.

So my idea is to have the above sensor, and let it check if something passes. If so, start the timer, if again, stop it. I have the code for that, but will the sensor detect it fast enough?

Little math:

  • approx. speed: 20 km/h -> 5,5 m/s
  • assumed "detection range" 1m (the wider the car is away the bigger it gets obviously as it has a 15 degrees angle)
  • the car will be in that range for approx 0,25s

Is that enough time for the sensor to detect a difference.

Speed could be lowered a little I guess, so maximum could be 0,5s.

If that is not suitable for such a project, any other ideas that do not involve having sensors on the other side of the track?

Any hint highly appreciated.

Cheers

PrimuS

What about retro reflective sensors?

Weedpharma

While that looks quite interesting, I think it may be a little "over the top" and from what I understand it still needs something to reflect on the other side of the Track?

Anything about the speed issue?

Cheers

These detectors use the reflected light to change state. It will change when the car goes past if it is within range.

Weedpharma

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