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Vibration Sensor

fish

Aug 13, 2009
3
Joined
Aug 13, 2009
Messages
3
Hey,

First post. Yay.

At the moment I'm designing a project which requires a reading a vibration sensor, something like this:

540626 on farnell.com (can't post URLs yet)
or
rapidonline.com 78-0768

Going by what I can gather, vibration causes the sensor to go into an unstable state. The datasheet says "the sensor reacts when disturbed by going into a fleeting change of state (i.e. n/o to n/c or vice versa). The settled state will be random unless mounting attitude is chosen for a n/c output".

I want to read this with a small microcontroller (a PIC10F, most likely), and I want to be able to detect when it is "disturbed". Given the rather awkward output, and my rather limited microcontroller capabilities, I'm going to need some kind of conditioning first.

I was thinking of having it input into an inverter to buffer the output, with a feedback loop to stabilise it. Then in theory I would get a 1 when there is vibration, and a 0 when there is none. I would then connect to a simple SR flip flop made from some NAND gates, and then use the micro to poll the Q output and clear the flipflop. I'd then use the micro to keep a running average.

I'm a tad worried about the signal conditining though, and I'm not entirely sure I understand when they say "fleeting change of state".

Does anyone have experience with such sensors that they could share?

Cheers,
 

docel

Sep 3, 2009
2
Joined
Sep 3, 2009
Messages
2
Hi!
This is a Mercury switch....meaning its just 2 terminals that will short or open when shaken by some vibration. The mercury, which is a liquid, will "vibrate" or make intermittent contact like a damped oscillation. It resembles the key bounce in mechanical switches.

The Manufacturers application circuit is quite sufficient for any of your purposes. If necessary, you can sample the signal with a delay routine for the Micro.
 

gosgirl

Sep 7, 2009
1
Joined
Sep 7, 2009
Messages
1
In theory I would get a 1 when there is vibration, and a 0 when there is none. I would then connect to a simple SR flip flop made from some NAND gates, and then use the micro to poll the Q output and clear the flipflop. I'd then use the micro to keep a running average.




MYCOLLECTS COM
 

amdNRA

Sep 3, 2009
50
Joined
Sep 3, 2009
Messages
50
Unless the vibration is great, the mercury switch may not be your best bet. Mercury swithes are mostly used as tilt indicators. A better vibration sensor might be a microphone with a reflector or a 4-6" speaker(used as a mic) coupled to a matching impedance transformer going to an amplifier, followed by a peak detector and a comparator whose output goes to the PIC chip. Play with the amplifier/comparator to vary the threshold of vibration.
Good luck, Gil. :)
 
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