Created: May 25, 2014
No description available.
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 connect to the battery supply, the other to the input of one of the gates. When water flows between the probes, the detection oscillator is gate ON. The alarm oscillator is gate 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.