Flood alarm

Description: The alarm circuit is designed using two audio oscillators, each comprised of two NAND gates. The detection oscillator is activated by a pair of remote probes, with one probe connected to the battery supply and the other connected to the input of one of the gates. When water bridges the gap between the probes, the detection oscillator becomes active. The alarm oscillator is triggered by the output of the detection oscillator, producing an audio tone of approximately 3000 Hz. The detection oscillator modulates this audio tone at a frequency of about 3 Hz, resulting in a distinctive pulsating sound. An 8-ohm speaker can be utilized to emit the alarm sound. The 2N3904 transistor can be substituted with any comparable NPN transistor. The circuit operates with a power supply ranging from six to twelve volts.

The alarm circuit utilizes two audio oscillators based on NAND gate configurations to create an effective water detection system. The first oscillator, known as the detection oscillator, employs two NAND gates configured in such a way that it remains inactive until both probes are bridged by water, completing the circuit. The probes are strategically placed in a location where water presence is to be monitored. When water flows between the probes, it creates a conductive path that activates the detection oscillator, allowing it to generate a square wave signal.

This square wave signal, typically oscillating at around 3000 Hz, is then fed into the second oscillator, referred to as the alarm oscillator. The alarm oscillator is designed to produce a continuous tone that is modulated by the detection oscillator's output. The modulation occurs at a lower frequency of approximately 3 Hz, which creates a pulsating effect on the audio tone. This unique sound pattern serves as an effective alarm signal, alerting users to the presence of water.

For sound output, the circuit requires an 8-ohm speaker, which is connected to the output of the alarm oscillator. The audio output can be adjusted based on the speaker's specifications and the power supply used. The circuit is designed to function with a voltage supply ranging from 6 to 12 volts, providing flexibility in power source selection. The 2N3904 NPN transistor used in the circuit can be replaced with any equivalent NPN transistor, allowing for component substitution based on availability or desired specifications.

This circuit exemplifies a straightforward yet effective approach to water detection, providing a reliable alarm system that can be easily implemented in various applications. The simplicity of the NAND gate configuration, along with the use of common electronic components, makes this design accessible for hobbyists and professionals alike.The alarm is built around two audio oscillators, each using two NAND gates. The detection oscillator is gated on by a pair of remote probes. One of the probes is connected to the battery supply, the other to the input of one of the gates. When water flows between the probes, the detection oscillator is gated on. The alarm oscillator is gated on by the output of the detection oscillator. The values given produce an audio tone of about 3000 Hz The detection oscillator gates this audio tone at a rate of about 3 Hz, The result is a unique pulsating note. Use any 8 ohm speaker to sound the alarm. The 2N3904 can be replaced by any similar NPN transistor. The circuit will work from any six to 12-volt supply.