How to Make a Flood Water Detector using LM555 IC

Flood water detector using LM555 IC is a perfect DIY project that can possibly save countless lives and properties in the event of flooding. Early detection and warning is our best tool to minimize the impact of this natural calamities. I am a living witness of how devastating this calamities are, how it claims thousand lives and how it destroys properties and dreams. I even seen a family that is drowned by flood at their sleep. If only they are warned that flood water is starting to creep inside their house, they would still be living today.

With this horrifying scene I witness and the fact that flooding is inevitable this days, me and my team decided to create this very simple yet effective DIY project, the Flood Water Detector using LM555 IC.


The Parts List

1 piece LM555 IC

1 piece 2N2222 Transistor

3 pieces 10K Resistor

1 piece 5Volt Buzzer

1 piece Tack Switch

1 piece 5Volt Power Supply or battery

1 piece perf board/bread board/PCB


The Schematic Diagram

flood water detector using lm555 ic schematic diagram


The Bread Board Circuit

flood water detector using lm555 ic bread board circuit


How it works

As you can see in the schematic, the LM555 IC is wired in a mono stable configuration with a twist. Instead the IC will automatically reset in a given period of time set by RC, a tact switch is provided to reset the IC and rearmed the circuit. The circuit is basically a flip flop that is set by the water sensor and reset with the tact switch.

Flood Water Detector using LM555 IC is compose of 4 sub circuits that is combined to give its functionality.

  1. The Water Sensor Circuit
  2. The Reset/Rearmed Circuit
  3. The Trigger and Latched Circuit
  4. The Siren Circuit

The Water Sensor Circuit is composed of the 10K resistor connected to the positive rail and a 2 pieces of metal rod which serve as the water detector. The 10K resistor provide a weak pull up voltage for the  trigger input (pin #2) of LM555 IC. When the two metal rod is shorted by the slightly conductive flood water it provide a path to negative thus pulling down the weak voltage provided by the pull up resistor and trigger the trigger input of the LM555 IC.

The Reset/Rearmed Circuit is composed of 10K resistor connected to negative and a tact switch connected to positive of the power supply. When the circuit is triggered by flood water it will stay latched until someone will press the tact switch to reset it or turn off the power. This is a fool proof feature to ensure that the user is will be aware of the situation before he will reset the alarm. This reset/rearmed circuit is basically a resistor and tact switch combination that is connected to the threshold pin (pin #6) of the LM555 IC which will be activated if a 3/4 VCC voltage is present in its terminal. The Tact switch will provide the necessary voltage for it’s activation by connecting the threshold pin to VCC.

The Trigger and Latched Circuit is the brain of the circuit. It will decide whether to trigger the siren or  not depending on the input signal from the water sensor circuit and latched in that state until a someone will reset it. This is very important in this kind of alarm circuit to get attention from the user first before it will be reset.

The Siren Circuit is the loud and noisy part of the circuit. No need to explain right?


The Flood Water Detector using LM555 IC in Action


The Conclusion

Indeed the Flood Water Detector using LM555 IC is very easy to build, practical and fun.

If you have any questions, suggestion or comments please feel free to leave us a message in the comment box below or through our Contact Us Page.


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