This simple device for preventing Bad flooding the floor in the room any conductive liquid or groundwater.
The design "flood alarm" is very simple (It is shown in Figure. 1), at the heart of which is immortal chip NE555. In the illustrated apparatus, this integalnaya chip operates as a gated oscillator tabular acoustic signals with a frequency of about 660 Hz. Generator starts at the time of, when the logic level on the U1 (output! R, output 4) is "1". This sorting is, when the electrodes, connected between the base of T1 and a power source, immersed in the liquid. A short press on the button JP1 allows you to check the device status.
In the case of using the battery as a power source, you should use the timer version 555. CMOS timer 555. As U1 is significantly increase battery life, that largely lead to operating costs. When, when controlled high resistivity liquid, T1 sensor amplifier is to use Darlington transistor BC517. Its use greatly increases the sensitivity of the device.
The circuit assembly "flood alarm" is shown in Figure. 2.