Water Activated LED Bracelet

Introduction: Water Activated LED Bracelet

About: Hi, welcome to my profile! :)

In this instructable I will show you how to make your own water activated LED bracelet!

The water activated LED bracelet is a multipurpose bracelet. The bracelet will light up when it makes contact with water. When it's raining, when you are swimming or when you are sweating. This bracelet lets you shine as never before!

Lets get started!

Step 1: Parts & Tools


  • 5mm LED
  • BC538 Transistor OR any other NPN transistor
  • 1k Resistor
  • CR2032 battery
  • M3 bolt
  • Electrical wire
  • Aluminium tape
  • Tape


  • Hacksaw
  • Soldering iron & solder
  • Hot glue gun
  • 3D Printer & Soft PLA

Step 2: Creating the Circuit

After we've gathered all the parts and tools we're going to create the circuit. The BC538 transistor has 3 pins. If the flat side is facing you, the Emitter is on the left, the Base is in the middle and the Collector is on the right. If you are using a different transistor there is a chance the emitter, base and collector are different. Look up the datasheet of the corrisponding transistor if you are not sure about it.

Supplies for this step:

  • BC538 Transistor (NPN)
  • 1k Resistor
  • Electrical wire
  • Soldering iron & solder
  • Hot glue gun


  1. Grab your resistor and solder the resistor to the base of the transistor.
  2. Solder two wires to each leg of the LED. After you've done that solder the negative side (blue wire in the image) of the LED to the collector of the transistor.
  3. Solder another wire to the positive side of the LED (this will be one of the probes).
  4. Solder a wire to the other end of the resistor (this will be the other probe).
  5. Finally solder a wire to the emitter of the transistor.

Step 3: Testing the Circuit

Now that you have the circuit it's time to test it!

Supplies for this step:

  • CR2032 battery
  • The circuit
  • Tape

How does the circuit work?

What you have just made is a simple water detector circuit. The transistor acts as a switch. Whenever the probes make contact with water, current will flow through the probes. This triggers the transistor. When the transistor is triggered, current will flow through the LED causing it to emit light.


  1. Use tape to connect the white wire (GND) to the negative side of the battery.
  2. Use another piece of tape to connect the red wire (VCC) to the positive side of the battery.
  3. Grab a glass of water and fill it with water. Put both probes in the water.
  4. OR Connect the two probes together

The LED should light up. If this isn't the case make sure the circuit meets the following things:

  • The battery is not empty
  • The transistor is wired correctly
  • The LED is connected correctly
  • The LED is not faulty
  • The transistor is not faulty
  • The wires are not broken

Step 4: 3D Printing the Bracelet

If you got the circuit ready it's time to 3D print the casing!

Supplies for this step:

  • 3D printer
  • Soft PLA filament

Printer settings:

  • Ender 3
  • 1.75mm Soft PLA
  • 20% infill
  • No supports
  • No raft
  • Nozzle temperature = 200°C
  • Bed temperature = 60°C

Download the STL files and start printing them both.

Step 5: Creating the Top

In this step we will be making two probe extensions.

Supplies for this step:

  • M3 bolt
  • Hacksaw
  • 3D printed top (see previous step)

We start off with a bolt which we will cut into two even pieces. These pieces will be the probe extensions.


  1. Grab the M3 bolt and mark two pieces of 1cm each.
  2. Use you hacksaw and cut the bolt at the markings.
  3. Grab the 3D printed top and place the two pieces of the bolt in the holes on the left and the right.

We are now ready to put everything in place

Step 6: Placing & Insulating the Circuit

In this step we're going to put everything into place.

Supplies for this step:

  • The circuit
  • CR2032 battery
  • 3D printed bracelet
  • 3D printed top
  • Aluminium tape
  • Tape
  • Soldering iron & solder
  • Hot glue gun

Steps for placing the circuit:

  1. Take a piece of aluminium tape and cut out a round piece the size of a CR2032 battery.
  2. Grab the circuit and use the piece of round aluminium tape to secure the red VCC wire in the battery frame of the bracelet. (image 1)
  3. Solder the two probes to the probe extensions we've made in the previous step. (image 2)
  4. Take the LED and put it in the hole of the top. (image 4)
  5. Grab the CR2032 battery and place it on top of the aluminium tape. Make sure the negative side of the battery is facing towards you.
  6. Use some tape to connect the white (GND) wire with the negative side of the battery. Cover the battery as much as you can.

Insulating the circuit

The circuit will be in contact with water all the time. An important aspect is that the circuit must be able to withstand water, LOTS of water. We're going to use the hot glue gun to glue all connections. This will prevent any short circuits.

Steps for Insulation of the circuit :

  1. Grab your hot glue gun and glue both legs of the LED. Make sure everything is fully covered.
  2. Use the glue gun to cover the transistor and resistor.
  3. Use the glue gun to cover the probes. (NOT the probe extensions in the top)

I didn't insulate the probes but it's better to do so. Whenever water gets in the housing the probes will detect the water. This will result in a LED which is constantly emitting light even when there is no water on the probe extensions.

Step 7: Finishing the Bracelet

We're almost done! The only thing we have to do is to put everything in the housing. After you have done that you can either choose to glue the top and the bracelet together or to keep it like the way it is

Supplies for this step:

  • Water

Whenever the probe extensions are making contact with anything conductive the LED will light up. As you can see my fingers are somehow conducting. This is most likely due to sweat.

Your bracelet is finally done! Show it off to your friends or use it to stay visible during a swimming session or during a storm.

I hope you enjoyed my Instructable and I will see you next time!

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    Question 2 days ago

    Hi how can I turn this into a blinking led instead of a solid light? I have no experience


    Hi! I would like to know if it is possible for the bracelet to be more sensitive by increasing the resistance. Also, would it be possible to set a timer that starts when the sensor first gets in contact with water? If it would be how would it work?
    Thank you!