crystals

[electroyas]

I thought of making crystals oscillator with stones for low freq. Is it possible ?

 

[BeerBelly]

Some of the older style crystals came in a holder with screws. I used to remove the crystals and etch them in an acid bath to get the desired frequency. I've never tried common stones. Crystals are ground at precise angles and may need to be grown to get the purity for these precise angles..


Let us know how this turns out.

 

[MikeMl]

Does stone have peizo-electric properties?

 

[unclejed613]

most common stones are metamorphic, igneous, or sedimentary, and consist of many smaller pieces. quartzite, for example is a metamorphic rock, consisting of many SiO2 crystals jumbled together, and as such doesn't have the required orderly molecular structure that a quartz crystal has. if you apply mechanical pressure to a slab of quartzite, many of the resulting voltage from the stresses on individual crystals within the quartzite would be randomly aligned, and you would get a zero, or pretty close to zero voltage as a result. many igneous rocks are amorphous, so there is no crystalline structure to speak of, and so would not be likely to be piezoelectric. sedimentary rocks are made of many discrete particles, like grains of sand, and suffer from the same randomness as the metamorphic rocks, and also tend to be easier to break apart under mechanical stress.

 

[throbscottle]

You may be able to find a natural quartz crystal where it's possible - this would would count as a "stone". Why not research the history of this and see how the inventor of crystal oscillators did it?

 

[unclejed613]

there are also ceramics that are piezoelectric.

https://en.wikipedia.org/wiki/Piezoelectricity

 

[KMoffett]

Perhaps a stone on a string. Think grandfather's clock. Both pendulums and quartz crystals require a power source and some form of feedback to continue oscillating.

Ken

 

[DerStrom8]

Is it possible ?

Short answer: No.

And I think all those who posted before me did a good job of explaining why. Crystals can't do much unless all the little parts are working together. In ordinary stones, however, assuming they contain crystals, they're all misaligned and working against each other. This is the "randomness" that unclejed spoke of.

It was a good thought, but unfortunately turned out to be unrealistic.

If you are trying to work on an actual project that requires a low-frequency oscillator, I'm sure we'd be able to come up with a more viable solution. So don't be afraid to ask more questions

Regards,
Matt

 

[BeerBelly]

Homegrown sugar crystal? Rock candy?

 

[Mr RB]

Musicians tuning fork next to a magnetic coil?

 

[electroyas]

Actually i made a circuit with op amps specified for crystal oscillator , when I connected a normal stone ,it gave some frequency but not sure whether it is the actual frequency for that stone. It gave some frequency even for granite i guess , but i took some time to come to a frequency , like slow beat then to a steady beat.

 

[JimB]

Crystals used in electronic circuits are made of QUARTZ.

Quartz is uses because it exhibits the piezo-electric effect. As already suggested, google it.

Granite and most other odd bits of rock found by the roadside DO NOT EXHIBIT THE PIEZO-ELECTRIC EFFECT.

It gave some frequency even for granite i guess

Whatever frequency your oscillator ran at, it was NOT determined by the lump of granite.

This whole idea is a fools errand.

JimB

 

[unclejed613]

it's more likely it oscillated due to the capacitor formed by whatever "plates" you had on the granite, and the granite acting as a dielectric

even if you have quartz crystals, they have to be cut along one of several specific axes and polished. the simplest way to make an oscillator would be to get a piezo buzzer, and connect it in place of a crystal. it will oscillate at an audio frequency, most likely somewhere around 2khz. there are other naturally occurring crystals, such as tourmaline or topaz that would qualify as a rock, and exhibit piezoelectric properties, and depending on the piece you get, may nor require precision cutting. when i was young, i had a book about rock collecting, and there was a description in there of how tourmaline could be used to demonstrate the piezoelectric effect in it's natural state.

 

[unclejed613]

and yes i had forgotten that granite is igneous, not metamorphic...**broken link removed**

 

[electroyas]

it seems it generated some freq due to the capacitance effect. Next i tried with sound resonance frequency incase i could get some feed back and amplify it, still i could not get the natural freq from a condencer mic. What kind of mic do i need to get for that? Then at least i can have a specific freq from normal rock .

 

[throbscottle]

Perhaps a stone on a string. Think grandfather's clock. Both pendulums and quartz crystals require a power source and some form of feedback to continue oscillating.

Ken

I love everything about this idea

 

[unclejed613]

it seems it generated some freq due to the capacitance effect. Next i tried with sound resonance frequency incase i could get some feed back and amplify it, still i could not get the natural freq from a condencer mic. What kind of mic do i need to get for that? Then at least i can have a specific freq from normal rock .

a condenser mic is a "one way" piezoelectric device, meaning it has a small preamplifier built into it, and signal only comes out... it's not truly a two terminal device in the same sense as a crystal. if you are trying to use a rock as an acoustic resonator of some kind, you need an actuator and a sensor, such as a sounder and a microphone both physically attached on opposite sides of the rock. this arrangement then becomes a 4-terminal device, much like a spring reverb in the way it's arranged and the way it functions.

 

[electroyas]

a condenser mic is a "one way" piezoelectric device, meaning it has a small preamplifier built into it, and signal only comes out... it's not truly a two terminal device in the same sense as a crystal. if you are trying to use a rock as an acoustic resonator of some kind, you need an actuator and a sensor, such as a sounder and a microphone both physically attached on opposite sides of the rock. this arrangement then becomes a 4-terminal device, much like a spring reverb in the way it's arranged and the way it functions.

Forgot to mention that I used a speaker and a mic, not only mic.

 

[unclejed613]

if you used a speaker and a mic, you probably got oscillation in spite of the rock being there. what you would want is to have some way of efficiently creating acoustic waves within the rock, and detecting them either at the opposite surface of the rock, or to detect reflections from the opposite surface (both methods are used in SAW filters... SAW=Surface Acoustic Wave). SAW filters are made of slabs of a piezoceramic with small electrodes plated on the edges. the piezoelectric effect sets up acoustic waves that pass through the ceramic, and either are picked up on the opposite side of the slab, or reflect internally off of the opposite edge and bounce back to a second set of electrodes near the actuating electrodes, but oriented in a way that the direct acoustic wave isn't detected, only the reflection.