Hello,

When the disk is oscillating, the AC on the signal will be higher.

Bertus

 

ok, I see. I'll order a hall sensor and do some tests. Thank you very much (especially Bertus) for the suggestions!

 

Hello,

When ordering a hall sensor, look for a linear type.
Then you can detect the amplitude of the AC.
You could even make a scale on a LM3914, the more AC the more leds will turn on.

Bertus

 

yes linear type hall sensor.. very hard to find in a ready to mount package..
I'll test it with an arduino and one led I think.. Thank you bertus!

 

Hello,

I have been using the KMZ10 from NXP in the past.
That is a bare hall-sensor bridge.
In this thread I have posted the datasheet:
http://forum.allaboutcircuits.com/threads/help-distance-sensor-project.24276/

Bertus

 

yes I found also something similar from Honeywell.. thank you for the suggestion!

 

A laser (or focused IR beam) across the face of the disc would become obscured if the disc wobbles off plane.

 

as I said, I cannot use optical solutions due to the possible dust..

 

Are you following the post " High speed Inductive proximity detector" ? same solution might apply to yours.

 

as I said, I cannot use optical solutions due to the possible dust..

Maybe an ultrasonic sensor directed at the face of the disc. A fluttering should be easy to detect.
Just trying to keep options open.

 

yes, thank you wayneh.
I thougth about ultrasonic sensor, but in my opinion they have some drawbacks..
They are expensive, and since the disk is not flat, it's difficult to handle the detection with the software...
I thougth also about an inductive proximity detector.. The problem with that is the sensing distance. Over 10 cm they become very expensive, and if I stay under 10 cm I risk to destroy the sensor if the disk oscillates too much..