A microcomputer (IBM-PC) interface for decoding ultrasonic telemetry pulse-modulated signals from either unisensor or multisensor (time-multiplexed) transmitters is described. Pulse intervals, recorded by the interface, and corresponding independently measured parameter levels (i.e., swimming directions, speeds, depths, water temperature, and ambient irradiance levels) are entered into a calibration file. The IBM-PC uses this file to convert the signal's pulse intervals to sensor states and displays these in real time. States of up to eight multiplexed sensors can be displayed concurrently in either numerical or graphical format (as histograms) with low resolution (16 axis divisions) or, for a particular sensor, with high resolution (70 axis divisions). The circuit components mount on the ffiM Prototype Card (with foil for interfacing logic) allowing easy installation in the IBM-PC's expansion slot. The 35K of controlling software is written in Pascal with four subroutines in assembly language.Describingthe behavior patterns of mobilemarine species (e.g., fishes, seals, dolphins, and whales) is a formidabletask. The potentialof ultrasonic telemetry transmitters for remotely identifying such patterns is great, especially when the number of sensors permitted in a transmitter is increased by the addition of a multiplexer (see Nelson, 1978). Methods of signaldecoding, however, have not kept pace with transmitter development. Decoding is still most often done by timing intervals on a stop watch and then finding the corresponding sensor state on a calibration curve (for current reviews of such telemetry methodology see Harden-Jones &Arnold, 1982, andHawkins &Urquhart, 1983
19and store telemetrydata using microprocessor-based systems. However, these are limited in their capabilities, processing only unisensor data and offering a single display of the data.We describe a microcomputer (ffiM-PC)-basedtelemetry decoderthat: (1) processes a pulse-interval-eoded signal into sensor states by interpolation or extrapolation based on a file containing tables of pulse intervals (PIs) and their corresponding behavioral and/or environmental measurements,(2) displaysuni-and multisensor measurements in real time, (3) plots the states of up to eight sensors as histograms with low resolution, (4) plots measurements from a single sensor with high resolution, (5) prints out a hard copy of recently acquired data, and (6) stores measurements on a floppy disk. This data can then be rapidlysearched withcommercially available database software (e.g., dBASE WIll) for important but infrequent behavioral events, and these events as well as associatedenvironmental factors can be studied in detail.
ULTRASONIC TELEMETRY SYSTEMThe resistive state of the sensor on the telemetry transmitter controls the time between successive ultrasonic pulses (in our case, ranging from 32-41 kHz). These pulses are converted by the receiver to either bursts of a 2-kHz pure tone or changesin transistor-transistor logic