Introduction: Light the Dark Necklace

Imagine wearing a necklace that automatically Illuminates when it gets dark and when there is enough lighting to become a normal jewel. A relatively easy and fun project especially for the one who wants to wear a jewel that literally shines! Take a look at my Facebook page for more of my crafts!

" There's the way that light shows in darkness, and it is extremely beautiful. And I think it essentializes the experience of being human, to see light in darkness "

Step 1: The Electronics

These are the electronics you're going to need:

  • 3mm Blue LED
  • Photoresistor
  • 20k Ω Resistor
  • Button Cell CR2032 3V
  • Button Cell Holder
  • Switch Slide SPDT
  • NPN transistor (2N3904)

Some of them can be replaced with some of your own variations. For example, the blue LED can be replaced with another color.

Step 2: Circuit Diagram

In the image above you can see the circuit and how everything is connected to each other. Some things that need to be highlighted are:

  1. If you change the resistance value (20K) to a greater or less, you achieve a greater response or the opposite to the sensitivity of lighting.
  2. In a higher Voltage Source, a resistor in series with the LED is required to limit the current through the LED and to prevent it from a burn. If the Voltage Source is equal to the voltage drop of the LED, no resistor is required!
  3. You can use a plethora of NPN transistors such as 2N3904 / BC547 / PN2222 / 2N4401. But must be careful with the pinout diagram , If you use the transistor that I have used on this project I have an image above that show exactly the pinout diagram.

For more experimentation but also to see in simulation the operation of the circuit I used the awesome Circuits by Autodesk Tinkercad.

Step 3: Live Testing

In this step we have built the circuit on a breadboard and we did some live tests. After that I just solder all together around the button cell holder and we are ready for the next step.

Step 4: The Pendant

The whole pendant was made with a 3d printer. For the dome, I used a transparent PETG filament which will diffuse the light from within but the light will also be able to pass through so that it can be used by the sensor. The lid of the pendant was made from black PLA filament and has a hole for the switch, we're going to glue the circuit we built before on the lid and just snap it in the dome.

The design was made with Autodesk Tinkercad and can you modified to your needs.

Here you can download the 3d print files:

Step 5: Final Details

What's left are the accessories to complete the necklace. You can easily see how everything is connected from the photos.

Step 6: Shine a Light in the Darkness

I think the result is a pretty special necklace that will amaze you and those who see it coming to life. Also, you can visit my ETSY shop illustrisWorkshop and see some of my wearables!

'' We all walk in the dark and each of us must learn to turn on his or her own light ''
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