21-09-2017, 04:00 PM
Aburst water supply hose from the washer, a bathroom faucet that you forgot to close, or a broken aquarium wall can turn your home into a pond. You can avoid this mess with an electronic water alarm that warns you of water leakage as soon as possible.
The acoustic water alarm circuit presented here takes advantage of the fact that tap water is always slightly contaminated (or has salts and minerals) and, therefore, conducts electricity to a certain extent. It is built around IC LMC555 (IC1), which is a CMOS version of the bipolar chip 555 timer. IC1 is followed by a complementary pair of emitter followers (T1 and T2) to drive a standard 8 ohm speaker (LS1). The power is supplied by a compact 9V PP3 battery.
Power is applied when the power switch S1 is closed. The reset input (pin 4) of IC1 is kept low by resistor R1 (2.2 kilo ohms). The astable oscillator connected around IC1 is in disabled mode. When the probes P1 and P2 are wetted, they lead to reverse the state of the IC1 reset terminal. As a result, the astable multivibrator begins to oscillate at a frequency determined by resistor R2 and capacitor C3. The output of IC1 drives the complementary pair of transistors T1 and T2.
Although this combination causes significant crosstalk distortion, it has no adverse effect on square-wave audio signal processing. A 10 kilo-ohm potentiometer (VRI) is inserted between the output pin 3 of IC1 and the bases of the transistors T1 and T2 for the volume control.
The probes can be made using two suitable copper needles or small pieces of circuit board with the copper surface coated with solder. Place them at the lowest point where water will accumulate. After construction, place the alarm circuit away from the point of possible leakage. Use a pair of fine twisted flexible wires to connect the probes to the circuit.
Capacitor C1 connected via input IC1 (pin 4 and GND) prevents the alarm circuit from responding to dispersed electrostatic fields. Similarly, twisting the wires together makes the relatively long connection between the probes and the circuit less sensitive to false alarms due to external electromagnetic interference. Finally, if you want to reduce the sensitivity of the probe, reduce the value of the grounding resistor R1.
The acoustic water alarm circuit presented here takes advantage of the fact that tap water is always slightly contaminated (or has salts and minerals) and, therefore, conducts electricity to a certain extent. It is built around IC LMC555 (IC1), which is a CMOS version of the bipolar chip 555 timer. IC1 is followed by a complementary pair of emitter followers (T1 and T2) to drive a standard 8 ohm speaker (LS1). The power is supplied by a compact 9V PP3 battery.
Power is applied when the power switch S1 is closed. The reset input (pin 4) of IC1 is kept low by resistor R1 (2.2 kilo ohms). The astable oscillator connected around IC1 is in disabled mode. When the probes P1 and P2 are wetted, they lead to reverse the state of the IC1 reset terminal. As a result, the astable multivibrator begins to oscillate at a frequency determined by resistor R2 and capacitor C3. The output of IC1 drives the complementary pair of transistors T1 and T2.
Although this combination causes significant crosstalk distortion, it has no adverse effect on square-wave audio signal processing. A 10 kilo-ohm potentiometer (VRI) is inserted between the output pin 3 of IC1 and the bases of the transistors T1 and T2 for the volume control.
The probes can be made using two suitable copper needles or small pieces of circuit board with the copper surface coated with solder. Place them at the lowest point where water will accumulate. After construction, place the alarm circuit away from the point of possible leakage. Use a pair of fine twisted flexible wires to connect the probes to the circuit.
Capacitor C1 connected via input IC1 (pin 4 and GND) prevents the alarm circuit from responding to dispersed electrostatic fields. Similarly, twisting the wires together makes the relatively long connection between the probes and the circuit less sensitive to false alarms due to external electromagnetic interference. Finally, if you want to reduce the sensitivity of the probe, reduce the value of the grounding resistor R1.