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.

This UHF transmitter is designed for low power applications as remote for garage doors and operating systems, wireless alarm. This UHF FM transmitter with only one transistor which works on frequencies reserved to low power airwaves signaling.

Transmitters frequency is FM modulated by an audio or digital signal applied in the common point of D1 or D2, through R3. The transmitter schematic can e modified to produce AM modulation by eliminating D1, D2, R2, R3 and R6, and short circuinting A and B points.

This FM broadcast rf amplifier is built with 2SC2539 which is a silicon NPN epitaxal planar type transistor designed for RF power amplifiers in VHF band mobile radio applications. It can deliver up to 15W at a 2W input power.

This dc converter raise a dc voltage at almost a double value and is useful for raising the output voltage of solar batteries up to the required level for charging acid or NiCad batteries. It can deliver up to 3Amps. The measurement values with 2A load are shown in the bottom table.
In this article we assume that the input voltage is 12V and the output is 22V. IC1a, R2 and C5 build a square wave generator. This signal is available in reversed form at IC1d output.
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