Passive acoustics are widely used to monitor the presence of dolphins in the marine environment. This study aims to introduce a low-cost and homemade approach for assembling a complete underwater microphone (i.e., the hydrophone), employing cheap and easy to obtain components. The hydrophone was assembled with two piezo disks connected in a balanced configuration and encased in a plastic container filled with plastic foam. The hydrophone’s performance was validated by direct comparison with the commercially available AS-1 hydrophone (Aquarian Hydrophones, Anacortes, U.S.) on different underwater acoustic signals: artificial acoustic signals (ramp and multitone signals) and various dolphin vocalizations (whistle, echolocation clicks, and burst pulse signals). The sensitivity of the device’s performance to changes in the emission source position was also tested. The results of the validation procedure on both artificial signals and real dolphin vocalizations showed that the significant cost savings associated with cheap technology had a minimal effect on the recording device’s performance within the frequency range of 0–35 kHz. At this stage of experimentation, the global cost of the hydrophone could be estimated at a few euros, making it extremely price competitive when compared to more expensive commercially available models. In the future, this effective and low-cost technology would allow for continuous monitoring of the presence of free-ranging dolphins, significantly lowering the total cost of autonomous monitoring systems. This would permit broadening the monitored areas and creating a network of recorders, thus improving the acquisition of data.

This work presents a hardware/software data acquisition system developed for monitoring the temperature in real time of the cells in Air-Cooled Polymer Electrolyte Fuel Cells (AC-PEFC). These fuel cells are of great interest because they can carry out, in a single operation, the processes of oxidation and refrigeration. This allows reduction of weight, volume, cost and complexity of the control system in the AC-PEFC. In this type of PEFC (and in general in any PEFC), the reliable monitoring of temperature along the entire surface of the stack is fundamental, since a suitable temperature and a regular distribution thereof, are key for a better performance of the stack and a longer lifetime under the best operating conditions. The developed data acquisition (DAQ) system can perform non-intrusive temperature measurements of each individual cell of an AC-PEFC stack of any power (from watts to kilowatts). The stack power is related to the temperature gradient; i.e., a higher power corresponds to a higher stack surface, and consequently higher temperature difference between the coldest and the hottest point. The developed DAQ system has been implemented with the low-cost open-source platform Arduino, and it is completed with a modular virtual instrument that has been developed using NI LabVIEW. Temperature vs time evolution of all the cells of an AC-PEFC both together and individually can be registered and supervised. The paper explains comprehensively the developed DAQ system together with experimental results that demonstrate the suitability of the system.

Passive acoustics is widely used to monitor dolphin presence in marine environment. The current study proposes a self-made/low-cost approach to assemble a complete and compact underwater acoustic recorder employing inexpensive and widely used components. The system is composed of two main elements: the computing unit (Raspberry Pi Zero 2W single board computer) and the sound acquiring sensor, i.e., a hydrophone based on a single-face piezo capsule disk (hydrophone cost ≈$10.00). The performance of the proposed hydrophone was preliminarily tested versus the commercial-available AS-1 hydrophone (commercial value = $395.00), during 30-minute acquisition sessions performed in a dolphin pool. The comparison was performed quantifying the capability of the two systems to provide a high-quality signal to assess echolocation clicks (EC), whistles (W), and burst pulse sounds (P) emitted by dolphins. Results showed that the worsening of performances introduced by the current low-cost approach is very limited since: 1) the average number of ECs detected over sixty selected 5-second portions of the acquired signal is not significantly different (146.6±66.7 for home-made vs. 151.1±73 for AS-1, p >0.05); 2) the total number of detected ECs is comparable (8797 vs. 9065, ≈3% difference); 3) the number of detected whistles is the same for the two devices (11); and 4) the error made by the low-cost approach in the detection of burst pulse sounds is lower than 7%. Looking to the future, this effective and low-cost technology will make possible to monitor dolphin presence over larger areas using a network of low-cost acoustic recorders.