A high-sensitivity drinkometer circuit with 60-Hz filtering

This article describes a drinkometer circuit designed to (1) detect licks even if the resistance of the skin on the animal's feet becomes quite high due to low humidity, (2) automatically adjust its triggering threshold and increase its gain so that it will continue to detect licks when the water delivery spout is partially shorted to ground by high ambient humidity, (3) reject 60-Hz signals so they will not be treated as rapid licks by the data-recording system, and (4) tolerate the high voltages that can occur if the subject receives an electric shock while drinking. This lickometer will be especially useful in situations where it is not practical to monitor for possible signal failure due to high or low humidity, or where 60-Hz artifacts may contaminate the signal provided to a recording computer.