Piezo Voltage Acticated Switch

I have a device that runs on 6Vdc power and transmits a signal when on. Its a beacon for oceanography. This device is normally off until it comes to the surface of the ocean where it must turn on. Other pressure switches have piston activated switches and other ideas that may work 70% of the time, but I think I have come up with something that will do a slightly better job.

The device will sit at the bottom of the ocean and need to be rated at 12000psi. I have though of using a potting compound to contain a piezoelectric crystal. When the device is signaled to release from its anchor it will begin its journey to the surface. As this happens it will experience a negative pressure change and a voltage will be produced until the pressure equalizes. I want to use this voltage to switch on the device so it uses its 4xC cell 1.5v batteries. I can come up with something that uses minimal current because the device will sit in the ocean for up to 2 years before it needs to be turned on.

I am on my last attempt at an alternative before I am forced to redesign the pressure switch and make it purely mechanical and I don't want to do that...I want to come up with something better...

How can I turn on a switch with a small and short voltage that will in turn turn on the device?

Even if it comes up fast the pressure change isn't going to cause that piezo crystal to supply very much current. Personally I think you should redesign the pressure switch. A simple cylinder of sealed ambient pressure air would work just fine, the cylinder would compress when it goes down more than a few atmospheres actuating the switch, and wouldn't extend until it came back up to the surface. I don't understand how that would be prone to failure.

The Orings often leak and crud can get on the piston and cause it to become immoble. I have seen a cct using a 2N2222 NPN transistor and a sound activated peizo here https://www.hiviz.com/tools/triggers/SNDTRIG.GIF

Maybe I can use this to switch it on? I just need to switch something on so it stays on.

Is the activation of the beacon mandatory needed at the moment it reaches surface or can it be delayed a few hours ?

Yes, the beacon must turn on when surfaced.

Weird, I thought I posted this...I found a sound activated piezo cct using a 2n2222 found here.

https://www.hiviz.com/tools/triggers/SNDTRIG.GIF

Make your own

Could I amplify the signal and get a switch activated using an opamp comparitor?

I can understand the concepts of electronics but I still have yet to use it to solve problems. I can come close but this is why I have come here, to the gurus.

I can supply power to it if the amphours are low ie under 20,000.

I have found a cct that uses a 2n2222 with a peizo sensor. Could it be modified and have a voltage switch on it?

You can find it here:

https://www.hiviz.com/tools/triggers/makeown.htm#st

Thanks.

That schematic seems to be for a strobe light, triggered by a piezopulse.
Is that the beacon meant for your device or is it a radio beacon ?
The quiescent current in that circuit may not leave much life on the cells when the moment arrives. I do not like the brutal flexion a piezodisc would suffer on such pressure differential. I would not be clicky fast either

Honestly am unsure to rely in 2 year old cells to make the beacon work.

Well, as it has to turn-on instantly when surfacing and cannot wait a few hours, my suggestion won't click. I would put small solar cells instead. If surfaces at night, Helius will show up soon. If during the day, you are done. Turns on when sees light.

The circuitry could be made with reverse bias a turn-on mosfet, in series with the solar cell(s) to force forward bias when illuminated. Or something like that; to be polished -latch-on.
The cells encapsulated behind a lens are impervious to pressures, no moving parts. At that depth it is black-black.
Well, good luck, come back with results.
Miguel

There is something similar to this being used in another industry but I cannot get plans for it. The solar has been explored and risks getting dirty or turning on at low depths. The mA-hrs of the batteries is quite high at about 33000, so I'm sure something could work. This is a puzzle that needs to be solved!

Unavailable plans is not a deterrent. Can be designed to your demands.

I still don't understand why the mechanical pressure switch is failing so frequently. It should be very very simply and reliable.

Because it has orings and they can get grime in them thus restricting motion and/or if there is anything on the oring that is missed during assembly then they will fail. Orings can also have defects in manufacturing. I wouldn't be going to the extent of asking for help if I didn't think it was worth it.

If you can help me then please help me design an amplifying switch with a voltage switch or any other ideas.

These are failing for whatever reason and a $10,000 piece of equipment is turning to crap. Some of these are failing upon second deployment...after being serviced and it is out of the scope of the warranty because it is now 2 years old.

Please help if you can.

If you told us what the voltage and current are generated by your piezo sensor, we would have provided a circuit already. A data sheet would be best of all!

Since no one here apparently has seen such a sensor, creating a design to match it is impossible.

zotz, what triggers the device to return to the surface?

The device is triggered to the surface by sending a signal to something called an acoustic release. This acoustic release is attached to the anchor at the bottom.

I have 6Vdc and the piezo can supply a voltage difference of 0.7Vdc.

So why are you using a pressure transducer? If even the approximate depth is know a simple timer could be tripped with the acoustic release to turn the transmitter on after enough time had passed for it to reach the surface, if it doesn't reach the surface by that time it probably never will.

The acoustic release and the other devices are not connected. They are a mooring held together by rope.

An alternative to the pressure switch is what I'm after. If the flash can be turned on my a peizo then pressure will turn it on. Can I use a low voltage relay switch?

zotzman, you seem to have a high opinion of piezo sensors, they produce virtually no practical current, any system that uses them would have to have an active amplifier working all the time. Probably no practical for a battery powered application that needs to last more than 2 years.

I still can't figure out why you won't use a properly encapsulated mechanical switch. If it's properly encapsulated you'll have no corrosion or buildup issues. Just coat it in something like silicone sealant, flexible so it'll transfer pressure but corrosion proof. Not sure how silicone would react under those pressures though you'd have to research the potting compound a bit.

It can be done and I have the resources to attempt it. If the sound activated flash can work then this will work. If you know of a voltage regulated switch or a opamp that will work then please let me know. Your suggestions have been attempted with high failure. You will just have to trust me on that. No one has come up with a more superior design yet and I think this will work.

zotzman said:

How can I turn on a switch with a small and short voltage that will in turn turn on the device?

Click to expand...

Any electronic switching circuit would work for your application.

So, here is what needs to be done, search out and get as much information on piezo, sensors, (google), then purchase if applicable one of each that could be a likely candidate for this application.

Then test each one and gather huge amounts of data, by placing them under changing pressures, simulating the greatest pressure they would be succomed to, then testing for leakage signals, as well as how they cooperate when the pressure changes, such as coming closer to the surface, there will be a changing output there too, that you must record.

Once all this is established then you can bring to the table this data, voltages and currents under different pressure situations, greatest amount of voltage change, and any residual voltage signal leakages while under a constant pressure, mark out the amount of voltage change that occurs incrementally at different pressure changes, so as to find the peak voltage, current output under the 0 pressure (when it is surfaced).

Then when you bring all that data to the board, there will be a logical way of implementing this device to operate as desired.

As of right now there is no electronic parameters to work in, so everyone is just guessing at how it could work, with no concrete analysis of what to do to make it work.

So you have a lot of research and development of testing these sensors, to where you know exactly what voltage , current, thresholds need to be met.
That a electronic switch can be activated with.