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Passive components for vibration detection?

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Dknot--

New Member
Hello,

I'm considering to do some vibration detection circuit. However, it seems impossible finding any passive components for vibration detection.

Idea is to detect vibrations of structures such as table etc. So, frequency would be in between few hertz and a few hundred hertz.

It does not really matter is capacitance or resistance etc changing with detected vibration, but discrete component should be low power.

Thank you already for answers/follow up questions,

Dknot--
 

cr0sh

Member
If the energy of the vibration is large enough, you could use a form of the "spring and nail" type sensor; basically a small switch made with a spring that is larger than a nail (or other metal rod), surrounding the nail - the nail forms one contact, the spring the other, and when the vibration occurs, the spring touches the nail. It can be made more sensitive by orienting it vertically and putting a weight on the spring to give it more mass.

Another possibility might be a "captured ball" sensor; basically a metal ball in a cage or wires (or a tube, or similar) - where when the mechinism is vibrated, the ball rolls and makes contact with wires/contacts and closes the circuit, which can be detected. In a way, its a variation on the old mercury switch that used to be popular.

I am not sure if they are still made, but back before MEMs accelerometers were popular, there were things called electrolytic capacitive tilt sensors; basically a device with liquid electrolyte and multiple contacts in a little capsule; they were driven with an AC waveform, and as they were tilted, capacitance changed between certain leads, and this could be detected (granted, this isn't passive like you wanted).

:)
 

colin55

Well-Known Member
We used a simple piezo diaphragm to detect 0.01 Hertz, when the front door of a house was opened or even when a person walked down a passage.
You could place the alarm in a room and it would turn on when a door (up to 10 metres away) was opened.
The detection was absolutley amazing.
 

Reloadron

Well-Known Member
Most Helpful Member
Some of this depends on how we look at components:

Passive:
Capable of operating without an external power source.
Typical passive components are resistors, capacitors, inductors and diodes (although the latter are a special case).

Active:
Requiring a source of power to operate.
Includes transistors (all types), integrated circuits (all types), TRIACs, SCRs, LEDs, etc.

So if I want to detect vibration in a table or maybe the ground (earthquake) my choice would be a piezoelectric device like a piezoelectric accelerometer which actually generates its own power and can very accurately measure vibration.

Anyway, even though a resistor or capacitor can sit there and have resistance or capacitance less a power source nothing really happens till power is applied I guess. Just the nature of the beast. :)

Anyway, as to passive I would run with piezoelectric accelerometer. That aside from mechanical devices that could visually display vibration but not accurately measure it.

Ron
 

House0Fwax

Member
Following on from what Colin said, years ago I opened up a car alarm and found the motion sensor to be a piezo disc with a spring soldered to the middle of the brass side. As I recall, the 'free' end of the spring had a 'blob' of something on it, it was very good at sensing motion. Too sensitive really, which is why I was 'in there', cutting the wires to it.
 

Dknot--

New Member
Thanks for answers!

If someone knows any cheap, commercial components for this purpose, let me know. Piezoelectric accelerometeres would be good choise I think.

Best regards,

Dknot--
 

Dknot--

New Member
Hi Colin55,

In my previous post I forgot to tell, that I'm looking for passive components. Current consumption of 0.5mA is greatly too much. Maybe 1uA would be suitable, best would be passive component.

Br,

Dknot--
 

Reloadron

Well-Known Member
Most Helpful Member
Hi Colin55,

In my previous post I forgot to tell, that I'm looking for passive components. Current consumption of 0.5mA is greatly too much. Maybe 1uA would be suitable, best would be passive component.

Br,

Dknot--

What exactly are you trying to do? What do you want the signal to look like? Do you want a specific level of vibration to trigger a flip flop and change states or do you want to see a signal on a scope that is a representation of the vibration like what an earthquake would look like (seismograph)?

Ron
 

Dknot--

New Member
Ron: Well, I'm doing trigger circruit. I would want that circuit is triggered when, let's say 10mg vibration occurs. Signal indicating vibration could be current, changing resistance/voltage/capasitance etc. It is not that important how the signal looks like, but current impulse/ changing resistance impulse etc would be great.

In my earlier post I asked about trigger circuit. If possible, I could use this vibration detection component in that.

Thanks colin55 for schematics!

Dknot--
 

Reloadron

Well-Known Member
Most Helpful Member
Oh OK, I got it. You could use a circuit as Colin proposed but I would do similar with some changes.

Years ago I was involved in a project to measure the time from when current in a coil decayed to a point (start a timer) to when the solenoid actually released (stop timer). To measure the stop we used an accelerometer similar to those pictured. I wasn't concerned with measuring the g force but only concerned with the "thump" sound made when the solenoid actually released.

I took the accelerometer output and ran it into an op amp for amplification. Then ran the signal into a comparator. The advantage was that I could adjust the comparators reference voltage so it would toggle at a given point of amplitude from the accelerometer. That in turn drove a 7474 D flip flop which would latch. The transition from High to Low on the FF would stop my timer.

Something al0ong those lines would likely work for you as a trigger. I don't have the circuit here at home but I could likely come up with something like it. The trick is setting at what level it triggers and thus I used a comparator to drive the flip flop.

Ron
 

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BrianG

New Member
Is it possible to use the shock sensor module from a car alarm? Those typically use a piezo device and can adjust the sensitivity, and some even have two stages of output (low shock and higher shock). Just an idea...
 

colin55

Well-Known Member
Is it possible to use the shock sensor module from a car alarm?
Simply solder a small machine-screw to the piezo diaphragm shown in the circuit above and it will act as an inertia detector.
 
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