Speed test

Hi, I want to be able to sense for the speed of a metal marble, as it travels past the orangutan perpendicular to it. i was thinking about using ultrasound ( i have a transmitter and receiver) so when the time for the ultrasound to return is less, that must mean the marble is passing. And when it is longer again that would tell you how long it took and therefore the speed. But there are problems. Ultrasound would cover an area larger than the face of the marble, so not all of the ultrasound would be broken at once. I then considered a laser beam, but it is such a narrow field that making sure it went back to the receiver would be quite difficult (also making sure it hit the marble would be difficult)

has anyone done anything like this before, and can give me advice on a good method to go about this



Can you use two break-beam sensors close together and then measure the time between the marble breaking the two beams?

- Jan

interesting. I’ve never heard of them, where do i look?


Shine a light (LED, laser pointer) on a sensor (CdS cell, phototransistor) and position the two so that when the ball reaches a certain spot, it keeps the light from reaching the sensor.

- Jan

Oh sorry yeah, I do know what you mean - light gates… Yeah the problem is its like a reflection off the ball back to the recevier - like a police speed gun…