This simple to construct water fishing thermometer circuit is intended to be used in sports applications like for example a fishing contest. A sensor measures the water temperature at a certain depth. A scale made of 16 LEDs shows the water temperature. With the knowledge about water temperatures and what types of fishes prefer what temperature, the fisherman can select the right bait.
The electronic fishing thermometer circuit is made of the UAA170 IC with additional components for the relevant temperature range of 4 to 190C. P1 is used to set the threshold level for the top LED. P2 is used to set the threshold for the bottom LED.
The input voltage is created through the voltage divider R2/NTC. The NTC is the temperature sensor. Its resistance is reverse proportional to the water temperature. If the water temperature is higherm the NTC resistance is lower resulting to a higher input voltage.
Constructing the sensor: shrink wrap the NTC and the soldered cable with a heat shrinkable tube then insert it into a brass tubing. Finally, pour epoxy into the brass tubing letting the NTC head protruding a little bit out of the tubing.
The entire water thermometer circuit with the 9-volt battery must be housed in a waterproof box. The bable that connects to the sensor can be marked for the different water depths.