Short Paper: An Ultrasonic Communication System for Biotelemetry in Extremely Shallow Waters Gregory Parsons (gsparson@ncsu.edu), Shaolin Peng (speng2@ncsu.edu), Alexander G. Dean (alex_dean@ncsu.edu) Motivation Collecting biotelemetry from underwater fauna such as the Blue Crab Tight constraints on size, weight, and battery life Operation in extremely shallow waters Short-range operation is acceptable Design History First Generation Second Generation Performance Field testing was performed in fresh water at Lake Wheeler just south of Raleigh, North Carolina Floating piers at the site were used as platforms for experimentation The depth in this area is less than 5 meters Transducers suspended 1 meter below surface Test1 was at 30 meters to evaluate throughput Test2 was at 100 meters to evaluate operational range, and performed at 31 baud for the percentage of packets received error free Receiver 3.8” x 2.5” Hardware tone decoders detect carriers Transmitter 3.8” x 2.5” DAC and amplifier generate outgoing waveforms Transmitter 1.1” x 0.7” Tuned LC circuit efficiently generates waveforms Solution The transmitter uses a tuned LC oscillator driven by an MCU timer to generate outgoing waveforms at the requisite 60Vp-p across a ceramic transducer Very low part count and an inexpensive 8-bit Atmel Atmega168 processor (1K SRAM, 8K Flash, 4 to 14MHz) that is both deployable in large numbers and disposable Four channel frequency-shift-keying Allows the processor to sleep while transmitting The receiver has gone through two revisions: Hardware tone decoders (NE567) to detect carriers Software solution utilizing the Goertzel algorithm to detect carriers Transceiver 2.5” x 1.5” Tuned LC circuit and software Goertzel algorithm handle both incoming and outgoing waveforms Energy Consumption Transceiver Board Current Draw at 2.8V Transmitter battery life of a 3V CR2450 lithium at 42 baud MCU LC Driver Amplifier Total Shutdown 4.6uA 0.10uA 0.70uA 5.4uA Idle 799.0uA 799.8uA Receive 3,470uA 724.0uA 4,194uA Transmit 1,060uA 22,400uA 23,461uA 94% Viterbi ECC 67% Without ECC Next Steps We will optimize our Viterbi decoder to obtain higher baud rates Parameterize the software modules for inclusion into the RaPTEX tool chain for ease of future development of underwater networks NCSU ECE Center for Efficient, Scalable and Reliable Computing This material is based upon work supported by the National Science Foundation under Grant No. 0509162. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).