Source for emergency ROV/Sonar recovery pinger?

Is anyone out there making reasonably priced locator beacons to aid in the recovery of lost subsea equipment? I’m aware of some high-end options, but it would be nice if there was a pinger priced less than the replacement cost of a new BlueROV…

Hi @StrikeLines,

This isn’t something I’ve looked into before - it could be useful to provide an example or few so we know what kind of features you’re after. I’m curious whether this kind of thing could be achieved with a Ping Sonar, I suppose along with a microcontroller, enclosure, and a battery…

I’m striking out with finding anything reasonably priced that really fills the role I’m envisioning. Here are the requirements as I see them.

The idea is to leverage sonar equipment already installed on offshore boats, so that we can quickly retrace our path, detect a beacon attached to the lost equipment and, mark some GPS coordinates that we can return to later with divers for recovery.

For my use case, (towed side scan sonar) here are the requirements:

  1. The pinger is small enough to attach to the towfish without affecting stability.
  2. It starts sounding after detecting a loss of power from the tow cable, and it has a battery life of several hours once activated.
  3. It pings with a frequency/waveform that interferes greatly with consumer fish finders. (In the 50-400 kHZ range.) It would need to create clear interference patterns and “noise” on the display of any fish finder passing overhead.
  4. Nominal depth of 50 to 600 feet.

The goal is just to allow survey crews in the field to quickly retrace their track, and mark the pinger’s GPS position with enough accuracy that a dive crew can come back later and recover it.

Survey crews know approximately where they were when the sonar disconnected. My hope is that they could turn around and search the area while watching for noise on the boat’s depth finder display. They could mark GPS positions where the pingers “noise” was displayed most strongly on the fish finder’s display.

If they can get within a hundred feet or so of the lost equipment’s location, there is a really good chance we can return with a dive crew or ROV and locate it pretty easily.

If a beacon like this was available for a few hundred dollars, I think it would sell like crazy. It’s cheap insurance, and it would give the boat crew on the water the ability to help locate the lost equipment before leaving the area. And it wouldn’t require any additional equipment or training for the boat crew.

As something of a case study:

This is an imprecise requirement - it’s hard to know whether a given sonar+battery system would meet it without a clearer description of “small enough”, which presumably depends on the size and weight of the towfish being used.

That should be achievable with an ADC on a microcontroller, possibly with a high-valued resistor bridge to keep the voltage in a measurable range while avoiding excess current draw. A slightly smarter circuit design may allow it to feed directly into the sleep/enable pin of the microcontroller, and save the effort of writing some code to parse it.

Given the intended purpose, the signal would likely need to go via a water-blocked connector to avoid the possibility of water leaking in through the wires when the tether has an open end from being cut.

Microcontrollers are low power. Sonars are less so, but power usage depends on the transmission power. Some effort could be put into having short pulses and long spacings to save power, which may be achievable “smartly” if the sonar is able to self-detect the distance to the water surface, or just via a connected depth sensor.

For reference, our Ping Sonar is specified as having a typical current draw of 100mA (at 5V), which is 0.5W. Assuming the microcontroller current is relatively negligible, running 0.5W for 4 hours would take a 2Wh battery, which is about the energy capacity of a single AA, so the battery likely won’t be a major cost contributor here.

I’m not very familiar with fishfinders. If they’re sensitive to the entire 50-400kHz range then that should be reasonably straightforward (e.g. the Ping Sonar uses 115kHz, which is inside that range), but if different ones are sensitive to different regions of that range it gets more complicated (because sonar transducers are generally tuned to maximise power at a specific frequency).

From a signal perspective this should be reasonably straightforward - doing regular transmissions of three closely-spaced equal-length and equal-strength pulses should be quite noticeable, as that’s not the kind of signal that could occur naturally. If multiple frequencies need to be covered then a transducer with a large bandwidth could be used to do repeated frequency sweeps.

A Ping Sonar has an “absolute maximum range” of 70m for detecting its own pulse reflections, so a detector with a similar sensitivity can likely detect a pulse from 140m away (which is ~460ft). That may be suitable/usable as-is, but could also be improved with a higher power or narrower beam-width transducer (although higher power may be more disruptive to marine life, and narrowing the beam width also reduces the area it’s detectable within).

The pressure should be fine for most of our smaller enclosures, so is achievable.

Our Ping Sonar is currently $360, and a 2" diameter acrylic enclosure at 100-150mm long is ~$120, so for the sake of round numbers we can say ~$20 for some batteries and a microcontroller, which brings the “material” costs from off-the-shelf parts to ~$500. If someone wanted to do the programming for free, and mounting / connection to the tether was left to the user, that’s still a chunk more than “a few hundred” (which my brain reads as “~300”), but is at least within the same ballpark.

If it was developed as its own product rather than a collection of parts then the material costs could be reduced a decent amount (e.g. the sonar electronics could be in the same enclosure as the batteries, and it may be possible to use the sonar’s microcontroller for everything instead of needing a separate one, but that then potentially loses the economies of scale of the available productised parts, and costs extra in engineering time and validation.

I don’t know what the demand would be for this kind of thing, but I imagine it wouldn’t have quite the same scale as our Ping Sonar or our watertight enclosure family, so it may not be viable to provide for much less than the “assembled off-the-shelf parts” option.

Regardless, I’ll pass the idea on internally in case there’s some interest in making it, or making changes that would make this kind of thing easier to do. If anyone else is interested then hopefully this discussion is a fruitful starting point :slight_smile:

Awesome, lets talk about this! I’m going to approach this from the angle of using a modified Ping sonar.

  1. Fair enough. Lets say, “No larger than a can of spray paint.” I don’t think weight will be a factor. Ping sonar, additional circuitry and battery should be small enough.
  1. I envision a solid state relay that closes and powers up the transmitter when external power is removed. I’d use a custom cable termination to “T” in where the tow cable connects to the sonar.

Very interesting! That simplifies things.

They are the same as any other transducer, and are all tuned to a certain frequency. If we wanted to be universal, we could feed a “chirp” type frequency sweep from 50 to 400 kHz into the ping and just know that the signal will be “loudest” at 115 kHz. Thus a ~100kHz receiver transducer would be most effective.

I agree. This is the area that I am most unfamiliar with. Could something like a Raspbery Pi zero be used to generate the signal waveform, and then we send that to the Ping’s transmit amplifier?

Even better, is it possible to modify the code on the Ping sonar’s directly? Could it be reprogrammed to start transmitting an arbitrary signal immediately upon powering up?

If so, then the problem is basically solved.

Let’s say I find time to do this as a personal project based on the Ping sonar. Here’s my approach:

  1. Buy Ping sonar. Reprogram it so that it begins transmitting 50-400kHz frequency sweeps at a rate of about 3 pulses per second as soon as battery power is applied.
  2. Buy 5V battery and a DC relay that can handle the 150-300V sonar tow cable voltage.
  3. Buy a waterproof power switch and a waterproof recharge port. (One of Blue Trail’s cobalt connectors would work.)
  4. Hook everything up, then permanently pot everything but the Ping Sonar into a solid block of epoxy.

The only part I’d need help with is reprogramming the Ping…

I think I’m going to make this.

Hey @EliotBR,

I got some specs from a commercial pinger. Do you know how Blue’s Ping sonar’s acoustic output compares to this?

Acoustic Output: 160.5dB re 1μPa @ 1m

Fair enough.

That could also work :slight_smile:

And yes, some form of T splice would likely be necessary to detect when power is available, unless you’re using AC power in which case you could also potentially measure it with current induced in a loop around the tow cable.

Fair enough, although there may be issues with trying to drive a narrow band transducer at any significant power level outside of its tuned range (it might crack, or build up excessive heat).

That would make the most sense, but is not currently available. I’ve passed it on internally that you’re a +1 on us providing an open firmware source template for people to modify and compile. I believe that’s something we’re planning to do, but we haven’t yet had the time to make a version we can publicly share the source for.

Unfortunately we don’t currently have significant testing data to verify the absolute acoustic output of the Ping Sonar. We’ve got a test setup, but I believe our latest testing has been focused on our next iteration of the sonar, which should have more complete data when it launches.