Building an ultrasonic underwater flash (strobe) trigger

Thread Starter

yt_1300

Joined Feb 18, 2023
22
I have used underwater camera set ups with both fiber optic cables and wires to trigger the external flashes (strobes), but I'd like to build a wireless rig. I realize that radio is probably out, but what about using an ultrasonic system? I have not found anyone who has done this and really don't know where to begin. It would need the following:

1. A transmitter that is attached to the camera housing and is triggered by a circuit being completed (this would ultimately connect to the cameras hot shoe so that pressing the flash completes the circuit in the hot shoe thus triggering the ultrasonic transmitter).
2). A receiver unit that is constantly listening for an ultrasonic pulse (at the frequency of the transmitter) and when detected, immediately closes a circuit, thus triggering the flash.

I realize that sound is much slower than light, but given that the strobes are <0.5m from the camera, it seems like the sound should get there plenty fast enough to keep up with the cameras shutter speed (mine doesn't go above 1/200th of a second when using a flash, whereas the sound should get there in roughly 1/3000th of a second).

Any thoughts on why this would be a bad idea?

Or, if it is not a bad idea, where do I go to look for appropriate transmitters and receivers? The googling I have done so far is mostly returning information about combined sender/receiver units to measure distances, which is not what I am after.

PS I have some limited experience with Arduino, so if setting this up via those boards is an easy route, that is an option.

Thanks
 

ericgibbs

Joined Jan 29, 2010
18,854
Hi yt,
Speed of sound through water is a nominal 1480 mtr/sec, depends upon the salinity.
E
Look around your local Yacht chandlers shop for suitable underwater transducers.
 

Thread Starter

yt_1300

Joined Feb 18, 2023
22
Why not put ordinary slave controllers on the remote flashes and use a flash on the camera to trigger them?
It doesn't work well underwater because the light scatters too much. It's possible, but not as simple as it sounds, and it limits my options because it means I have to use an onboard flash. Thanks though
 

Thread Starter

yt_1300

Joined Feb 18, 2023
22
Hi yt,
Speed of sound through water is a nominal 1480 mtr/sec, depends upon the salinity.
E
Look around your local Yacht chandlers shop for suitable underwater transducers.
I live in Belize, so things like electronics pretty much have to be ordered online and shipped down here
 

Ya’akov

Joined Jan 27, 2019
9,169
It doesn't work well underwater because the light scatters too much. It's possible, but not as simple as it sounds, and it limits my options because it means I have to use an onboard flash. Thanks though
What is the maximum distance from the camera to the strobe?
 

AnalogKid

Joined Aug 1, 2013
11,053
I understand what you are trying to do, but this seems like a lot of work to eliminate a very short cable. Can you expand on what is to be gained? It will help point us in the right direction.

ak
 

Thread Starter

yt_1300

Joined Feb 18, 2023
22
I understand what you are trying to do, but this seems like a lot of work to eliminate a very short cable. Can you expand on what is to be gained? It will help point us in the right direction.

ak
I have multiple strobes which means multiple cables, and the cables make the whole rig more time consuming and awkward to set up on a dive boat, as well maneuvering it under water (sometimes I am in tight environments where anything extra to get snagged is a problem). Additionally, they create multiple additional failure points (a strained wire recently made my flashes inoperable on a trip). So overall, I'm just really unhappy with the wired situation.

I should also add that I am building my rigs from scratch, so simply having a single transmitter with a receiver on each flash would actually simplify my life tremendously.
 

AnalogKid

Joined Aug 1, 2013
11,053
There are a lot of noises under water. What is the maximum delay you can tolerate between triggering the transmitter and the flashes going off? I ask because filtering and/or signal processing to reject unwanted sounds takes time. For example, light-beam alarms for garage doors or industrial machines usually modulate the light with a frequency such as a few kHz so the receiver can differentiate between the beam light and ambient or sun light. If you do a similar thing with sonics, then the longer the receiver has to process the signal, the fewer false triggers there will be.

ak
 

Thread Starter

yt_1300

Joined Feb 18, 2023
22
There are a lot of noises under water. What is the maximum delay you can tolerate between triggering the transmitter and the flashes going off? I ask because filtering and/or signal processing to reject unwanted sounds takes time. For example, light-beam alarms for garage doors or industrial machines usually modulate the light with a frequency such as a few kHz so the receiver can differentiate between the beam light and ambient or sun light. If you do a similar thing with sonics, then the longer the receiver has to process the signal, the fewer false triggers there will be.

ak
That's a good question. Most of the noises underwater are not ultrasonic (unless I'm in a pod of dolphins), so my hope was that receivers would be pre-programmed to only detect a narrow frequency band, but I'm a towering mountain of ignorance about these things.

I'm not surely exactly how much of a delay could be tolerated, but I'm gonna guess that it would be about 1/100th of a second max
 

Janis59

Joined Aug 21, 2017
1,849
RE:"" where do I go to look for appropriate transmitters ""
Let obtain the Princess Diana lighter. In early 90-ies Diana was initiated the pedestrian landmines global forbid, thus the billions of detonation initiators was left unused. Then someone found it may well serve as the LPG lighter igniting element, thus was produced tens or even hundreds of billions lighters for very cheap 8 cent price, later 12 cents and nearer to millenia 20 cents per piece. Every lighter consisted of small gas tank and piezo rod hammered at ignition, thus making out the high voltage pulse. It well works also vice versa, exaert the U-sound pulse when fed my HV pulse. Sad the all piezo rod stock at last was emptified thus last 10-15 years I havent seen only lighters with a riffled roller type.
 

AnalogKid

Joined Aug 1, 2013
11,053
I suspect that approximately 0% of post #12 is correct. Depending on how you define things, there are at least three different types of land mines, and Princess Diana's campaign led to a treaty covering only one of them. Notably, the US, Russia, and China are not signatories. Following the treaty, worldwide production of land mines decreased only slightly, There were not hundreds of billions of ignition elements laying around unused; that's at least 12 for every man, woman, and child on earth. And, component stockpiles were intentionally reduced over several years before the treaty was enacted.

Beyond all of that, a piezo ignitor, such as the one in my outdoor grill or in every BIC fire starter, basically is a small rock. It has no diaphragm for moving air, and actually is the exact opposite of what is required. An ignitor converts mechanical force into electric voltage/current, while an ultrasonic transmitter takes electrical voltage/current and converts it into mechanical movement.

ak
 

Janis59

Joined Aug 21, 2017
1,849
OK about Diana, but at Europe just few weeks after that treaty all shops became full with those igniters tenfold cheaper as classical <roller plus stone> type. But what most important, it was about 4 mm thick and more than inch long. When this rod is fast bended for about 1 mm then 3 kV are generated, but when 3 kV are attached to it poles, the rod is bending by about milimeter. Thus, ir perfectly works both directions and You heavily miss the physics, sorry, if vote it may work only unidirectionally. All the piezoceramics may work in both directions.

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