PICmicro® MICROCONTROLLERS (MCUs) IN BIOTELEMETRY

In the Department of Marine, Earth & Atmospheric Sciences at North Carolina State University, PICmicro® MCUs help marine biologists Tom and Donna Wolcott see what crabs (and other creatures) are up to when direct observation is impossible. Some examples of PICmicro-based biotelemetry:

CRABS, LOBSTERS AND SHARKS

How do aggressive interactions between Chesapeake Bay's famous blue crabs affect their predation on patches of clams? Crabs, wearing PIC16C54-based transmitters, were released into large field enclosures containing patches of prey. The PICmicros encoded the data (individual ID of each crab, whether it was performing a threat display, and when it was feeding), synthesized the ultrasonic frequencies, and drove a transducer directly to telemeter the information. PIC16C54-based receivers on the four corner posts of the enclosure decoded the transmissions and relay data to a shore station, which used time of arrival of the signal at each corner to calculate the crabs' positions and log who had moved and/or changed behaviors. The result: crabs do show more aggression when feeding, and when more crabs are present the survival rate of clams actually goes up as the crabs interfere with each others' foraging.

How do mature female blue crabs make their way down-Bay to spawning grounds in the high salinity waters near the Bay's mouth? Our latest crab transmitters incorporate a biopotential preamplifier to detect chewing (feeding) and a module to sense pressure. They will tell us if the females rise up into the water column to ride ebbing tides, and whether they spend the rest of the time feeding on the bottom to build up resources for making eggs.

Other PICmicro-based transmitters have been designed to monitor foraging and locomotion of American lobsters, and swimming activity and energetics of young sharks.

DINOSAURS

Were the dinosaurs warm- or cold-blooded? Oxygen isotope data from fossils suggest that bones near the core of a dinosaur's body (e.g., body vertebrae) may have grown at different temperatures than those at the periphery (e.g. toes, vertebrae at tip of tail). To interpret the data from fossils, our collaborators in paleontology and veterinary medicine need to know the pattern of bone temperatures in different body regions of unrestrained, normally-behaving "contemporary dinosaurs"--both cold-blooded (alligators) and warm-blooded (ostriches). A transmitter built around the PIC16C620 telemeters the resistance of seven temperature sensors inserted next to bones, and of one reference resistor. It sends the information over the FM radio band, so that a decoder board between the earphone jack of a portable FM receiver and the serial port of a laptop computer can transfer the data to the screen and right to disk. The prototype transmitter (here modeled by an unagressive rubber alligator) and the miniaturized version (hidden in a large plastic box so the ostrich wouldn't swallow it) have provided volumes of data from active, normally-behaving animals.

BIOTELEMETRY TRAINING AT NCSU

A biotelemetry techniques course is offered by the Department of Marine, Earth and Atmospheric Sciences, emphasizing the spectacular variety of information that now can be sensed and telemetered from even quite small animals. The participants' ultimate challenge is to design a telemetry system for one participant's research. An example is the transmitter one class designed for a veterinarian exploring movements of feral housecats. Exploiting the capabilities of the PIC16C54 to process data on the animal before transmitting it, the transmitter stored data and once per minute provided a synopsis of the cat's activities over the last 24 hours. This allowed the investigator to get the data by tuning in to each instrumented cat only once or twice a day, and thereby monitor multiple subjects rather than having to follow a single cat continuously.