01 / Abstract
Abstract
The first version investigates short-range underwater digital communication without claiming field-ready range or pressure tolerance. Electronics stay dry while two low-voltage piezo elements are characterized, submerged, and used to transmit repeatable packets across a controlled freshwater test tank.
02 / Use cases
Use cases
- Low-rate telemetry from a submerged sensor node.
- Command and status exchange with a small underwater robot.
- Experimental comparison of acoustic, optical, and magnetic-induction channels.
03 / Theory
Operating theory
Acoustic propagation
Sound travels well through water, but frequency-dependent loss, reflections, and tank multipath distort transmitted symbols. The carrier must be selected from measured transducer response rather than assumed specifications.
Binary frequency-shift keying
Two measured tones can represent binary data. A tone detector such as a Goertzel implementation trades data rate for simple, explainable demodulation.
Analog signal chain
The receiver needs input protection, high-impedance amplification, band limiting, and enough sampling bandwidth to preserve the selected carrier.
04 / Requirements
Requirements and success criteria
- Keep mains power and exposed electronics away from the water test volume.
- Characterize each piezo in air and water before choosing modulation tones.
- Deliver a 16-byte CRC-protected packet at least 90 times out of 100 across 1 m of freshwater.
- Record frequency, receive amplitude, packet error rate, current, and water conditions.
05 / Architecture
System architecture
06 / Current status
Current status
Inventory and literature have been reviewed. Piezo discs, amplifiers, microcontrollers, and test equipment are available, but transducer response, waterproofing, use case, range, and depth requirements are not yet validated.
07 / Next steps
Next steps
- Choose sensor telemetry, robot command, or diver messaging as the first use case.
- Lock freshwater or saltwater, target distance, and test depth.
- Measure piezo impedance and receive response with the Analog Discovery.
- Demonstrate one detected ping before implementing packet modulation.
- Prototype binary FSK and record packet-error data.
08 / Risks
Risks and constraints
- Pickup discs are candidate transducers, not calibrated hydrophones.
- Small tanks can create severe reflections that invalidate naive range conclusions.
- Waterproof does not mean pressure-rated.
- The prototype is not suitable for life-safety or diver-critical communication.
09 / Artifacts
Engineering artifacts
- Research reading list
- Planned transducer-response measurements
- Packet format and decoder firmware
- Packet-error and power-consumption test report