Motion Detector?

[joe_1]

Hi

I have two metal plates. One is rotating, and the other is static. I want to detect the moving plate whenever it passes over the static one. The distance between them is about 1" (2.5cm).
I can put any electronic components on the static plate, but I can't have anything electronic on the moving one.
I am not sure how to approach it, any idea will help.

Thanks in advance.

 

[akg]

Hi

I have two metal plates. One is rotating, and the other is static. I want to detect the moving plate whenever it passes over the static one. The distance between them is about 1" (2.5cm).
I can put any electronic components on the static plate, but I can't have anything electronic on the moving one.
I am not sure how to approach it, any idea will help.

Thanks in advance.

put a small magnet in the rotaing plate and a reed switch in the static plate.

or if the rotating plate can reflect , use an led/ldr couple , so that light from led will be refledted back to the ldr by the rotating plate(for low speed, use IR+PD for high speed)