How to test Rochelle salt piezoelectric crystals voltage oscilloscope

How to test Rochelle salt crystals or piezoelectric crystals. In this case I measure the voltage using an oscilloscope. I also give a few pointers on how to use the oscilloscope. I also show that the crystals have polarity.

See also this video on how to make Rochelle salt crystals:
http://www.youtube.com/watch?v=E1Ct3VUWvhQ

For more see:
http://rimstar.org/materials/piezo/rochelle1.htm

To see how to make a larger crystal from a seed crystal:
http://www.seawhy.com/xlone.html

- http://rimstar.org

Category:

Science & Technology

Tags:

• How-to
• test
• rochelle
• salt
• crystals
• piezoelectric
• piezoelectricity
• measure
• voltage
• oscilloscope

[mahela1993]

What does the reading look like if, instead of tapping the crystal, you apply sustained pressure on the crystal?

[RimstarOrg]

@mahela1993 I knew what the answer would be but I just tried it out anyway. I don't get anything different than when the crystal is just sitting there - so no effect.

[mahela1993]

@RimstarOrg Thanks for the reply.

But why doesn't a voltage develop when the crystal stays deformed (due to the sustained pressure)?

[RimstarOrg]

@mahela1993 I don't know and can't seem to find an answer. If you find out let us know.

[aardvarkmikey]

How did you use the smaller crystal as a "seed crystal" to grow the larger one?

[RimstarOrg]

@aardvarkmikey You create another batch of the solution like when you made the seed crystal. Then you hang the seed crystal from something like a fishing line in this new solution and let it sit. Keep the temperature very constant. I put the container in a styrofoam box in a closet. I'll put a link in the video description but basically that's the idea.

[aardvarkmikey]

awesome! Thank you!

[RimstarOrg]

@MichaelAChang Thinking more of what you want to do - It would still be very hard and I don't know how well it would work, but you could do as in my "previous How-To" video. Then select a flatish crystal that tests the way you want and use that as a seed crystal to make a larger one. The larger one would be made in a flatish container with a PCB bottom. See the last part of the "How to make a Rochelle salt crystal" page on my website. A link is in the description of the "previous How-To" video.

[RimstarOrg]

@MichaelAChang Interesting. I don't know if pouring the solution out on a copper clad PCB would work. I have my doubts it would work on your first attempt. You'd probably have to do a number of tries to find out. The batch I made this time didn't give as many crystals as the batch I made a few years ago, and yet it was the same recipe. So there are variables to play with, probably temperatures in my case since I didn't strictly monitor and control that.

[MichaelAChang]

I'd like to try making some using your "previous How-To" video as a reference, but instead of making clumps, to make sheets dried on a copper clad PCB to facilitate soldering. Any reason why that wouldn't work?

I have tested those standard piezo discs glued to the dust cap of a 15" woofer as a motional feedback sensor. It worked quite well, and I was surprised by the response linearity.