Flood alarm

Posted on Jun 7, 2012

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

Flood alarm
Click here to download the full size of the above Circuit.

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.

Leave Comment

characters left:

New Circuits



Popular Circuits

Discrete component motor direction controller
Knight Rider Running Light Schematic
12v stroboscope 250 400v dc circuit
1.3V Power supply
games timer 2
BH1417F FM stereo transmitter electronic project
PNP Transistor Analysis
Digital Remote Thermometer
650mA Micropower Low Noise Boost Converter with Output Disconnect