HOW TO DRIVE A PIEZODEVICE

Hi Bob,

Depending on how loud you need the sound to be you could conceivably drive the piezo directly off a 555 timer. There are also little piezo buzzers with a built in oscillator that could be incorporated in an even simpler circuit. Give me a little more information on your requirements and what parts you already have and I will draw up a suggested circuit. you suggest a frequency of 50 or 60 Hz but this is quite low and would be more like a hum as oppose to a beep or a ping.

John

End result I want to make a unit that will measure distance underwater. 

It has to be omnidirectional.  Transducers for depth finders and fish

locators are somewhat directional in a 60 deg. cone.  I have seen on the

internet if you put a piezo device in a small plastic container filled

with mineral oil it will work as a transducer able to send out a ping. 

Then you are set.

I want to use a Arduino to control the device.

Bob

Hi Bob,

Thanks for the additional information. The complexity of what you describe is above my expertise. I am also confused about what you mean by an omni-directional distance measuring device. Such a device would need to return a three dimensional surface that is representative of the distance to objects in all directions. Also there would still be granulation as the resolution would have to be limited. Perhaps it would be easier to build a device like the fish sonar and then use it to sweep and return directional data. You could then integrate the directional data to yield a more complete picture. Once again I apologize for not being able to help further on this project. I hope you are able to find someone with more knowledge to assist.

John

Just a small addendum. Your specified frequency of 50 to 60 cycles would yield very low resolution data but it would have a greater distance of penetration. Higher frequency sound would give much better resolution but at the cost of distance.

John

This sounds very interesting and boy would that be cheap if it worked well! LOL! I would first do a conductivity test on the mineral oil. I'm guess minerals in the oil will add to conductivity unless it's not exactly minerals? What I mean by that is that I'm not sure exactly what is in mineral oil. I actually worked in the ROV business for years as a Lead Tech. I've never heard of this but that doesn't mean it can't be done. Once you find that the mineral oil is non-conductive (Infinite resistance reading) then try to proceed. Don't waste a lot of time on people that like to waste peoples time. ;-) If all is good then I would think it would be easier to use a different piezo to receive the ping result. Just a thought though. Also remember that water creates 0.739 lbs per foot of depth. So intrusion is critical at any point of the wires not properly sealed. Good luck! :-)

I think you are a bit mislead here - it is common to use a transducer immersed in oil to couple it through the fiberglass hull of  a boat.

Check this reference:  www.stowemarine.com/Depth_In_Hull.pdf

To find out more Google 'omnidirectional underwater ultrasonic'

lots of hits and lots of information.

I have designed piezo sensors in the past and it isn't easy - we used a mega expensive FEA package (ANSYS) and lots of fancy test gear. If you need a decent performance then buying them is much more practical. I've had soem acceptable results from very low cost Chinese parts.

MK

How am I mislead?

I understand the use of transducers but I've never heard of using a piezo buzzer to try to produce sound through mineral oil or any fluid for that matter. I was just stating that experimenting wouldn't hurt but your post stated knowledge that will probably save him the time and effort which I'm sure he would appreciate. ;-)

Sorry Jon, I was replying to Bob when he said:

I have seen on the

internet if you put a piezo device in a small plastic container filled

with mineral oil it will work as a transducer able to send out a ping. 

The point I was making is that you put a complete ultrasonic transducer into the oil, not just the piezo element (as shown in the Stowe Marine reference).

MK

No problem. These forums have so many dang buttons! LOL!

It's cool that you have worked more in depth on these devices. Offshore we only figured out if the device or the system had an issue. If the device had an issue then we just replaced it then would send it in for repair. ;-)

Why not use sonar?

C