Easy Water Overflow Alarm Using Household Scrap

Step 1: Prepare the 5V Charger

Find an unused 5V mobile charger—make sure it’s still working properly.

Now, carefully open the charger case using a screwdriver or a cutter.

We need access to the internal DC output wires, usually marked as + (positive) and – (negative).

⚠️ Be cautious while opening—ensure the charger is unplugged to avoid any shock or injury.

Step 2: Mount and Prepare the Charger PCB

Fix the charger’s PCB securely on a base or stand to keep it stable while working.

You’ll see the USB socket on the board—remove it carefully using a desoldering pump or any suitable method.

After removing the socket, you’ll find two pads or tracks where the USB pins were.

These are your + (positive) and – (negative) output points.

Use a multimeter or inspect the PCB markings to confirm the polarity before connecting anything.

✅ Mark the + and – clearly to avoid mistakes later.

Step 3: Prepare and Place the D882 Transistor

Take the D882 transistor and bend the emitter leg as shown in the image (usually bent backward).

Cut the other two legs (base and collector) slightly shorter for neat placement.

Insert the emitter leg into the +ve (positive) side of the removed USB socket hole on the PCB.

Apply a small drop of glue (like hot glue or super glue) to secure the transistor in place.

This setup will make your circuit cleaner and more stable.

Step 4: Connect the 100Ω Resistor and LED

Take one 100Ω resistor, cut the legs to a suitable length.

Solder one leg of the resistor to the base pin (center leg) of the D882 transistor.

Next, prepare the 5mm LED by bending its legs to fit the PCB as shown in the image.

Insert the LED’s negative leg (cathode) into the –ve (negative) side of the removed USB socket hole on the PCB.

Solder the positive leg (anode) of the LED to the other leg of the 100Ω resistor connected to the D882.

After soldering, cut off any excess length from the LED legs for a neat finish.

Step 5: Add Another 100Ω Resistor for Sensor Input

Take the second 100Ω resistor and solder one leg to the base pin (center leg) of the D882 transistor—on the same point where the first resistor is connected.

Cut the other leg of this resistor slightly, leaving enough length to later connect a water level sensing wire to it.

This resistor will act as a current limiter for the signal coming from the water probe.

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Step 7: Connect Power Output Using 2-Pin Connector

From the back side of the PCB, solder two wires to the +ve and –ve output points (where the USB pins were previously removed).

Take a 2-pin connector and fix it near the USB area using a drop of glue to hold it firmly in place.

• Solder the +ve wire (from emitter leg / USB + pad) directly to one pin of the 2-pin connector.
• Take the other pin of the 2-pin connector and connect it to the free end of the 100Ω resistor that was soldered to the base (center pin) of the D882.

This 2-pin connector is where the sensor wires (probes) will be connected later.

Step 8: Install the Buzzer

Once the circuit is complete and tested, take the top cover of the charger case.

Drill or make a small hole at the center side of the top cover, as shown in the image.

Take a buzzer (5V type) and insert its wires through the hole.

Place the buzzer on the case and fix it using short screws.

⚠️ Do not use long screws—they may touch the internal circuit and cause a short when the case is closed.

Step 9: Connect Buzzer Wires and Final Assembly

Solder the +ve wire of the buzzer to the +ve pad (where the USB + was connected or directly to the + pin of the connector).

Solder the –ve wire of the buzzer to the base pin (center leg) of the D882 transistor, before the resistor.

Once the buzzer is wired correctly, carefully close the charger case and make sure all internal parts are secure and not touching.

After closing the case properly, make a small hole on the top outer side of the case—this allows the LED to be clearly visible when the tank is full.

Step 10: Connect the Water Sensor Wires

For testing, you can use short wires, but for real use, you’ll need longer wires to run from the tank to the adapter inside the house.

Here’s how to set up the water sensor:

• Take two wires and connect one end of each to the 2-pin connector on the adapter circuit.
• On the other end, you’re using a smart trick—take a 2-pin connector, open it, insert and screw the wires tightly onto the two metal contacts, then close the connector.
• Place or fix this connector at the desired water level in the tank.

When water touches both pins, it will complete the circuit, activating the LED and buzzer to alert you that the tank is full.

✅ This is a simple, effective, and reusable probe setup without soldering at the tank side.

Step 11: Demo & Final Result

You can see the full working and demonstration of this water tank alarm in the video below:

🎥 Watch Full Video Here

This simple and cost-effective DIY project helps prevent water wastage using an old mobile charger and basic electronic components. No programming or microcontroller needed!