NeckLight : a PCB Necklace for Humans and Dogs

Hello everyone, this project is my first Instructables so I will try to do my best.

In this project, I will explain you how I managed to create this PCB necklace that glows in the dark ! To be honest, this is the perfect project if you want to learn about the surface-mount electronics assembly process.

First of all, let me tell you that it was inspired from this project : https://www.instructables.com/id/LED-Jewelry/ made by jiripraus so please, have a look ! When I first tried doing his project I failed terribly and I told myself "Why not use a PCB instead of using straight brass rods ?" So... TADAM this project came to my mind !!!

The initial goal of this project was to make a custom gift to my girlfriend.

On the 3rd picture, you can also see my dog, his name is Baba and I think he is wearing this necklace perfectly ^^ (He looks a little bit like Tony Stark, don't you think ?)

I buy all my stuff from aliexpress, but I'm sure you can find these supplies and tools on other websites.

• 1x Custom PCB (for myselft made by JLCPCB)
  • 5 PCB for 2€
• 6x Multicolors SMD 1206 Led https://www.aliexpress.com/item/32828391530.html?...
• 6x SMD 0805 Resistor (a SMD resistor sample book will be your best friend in a lot of projects) https://www.aliexpress.com/item/32694344850.html?...
• 1x CR2032 battery https://www.aliexpress.com/item/33019330792.html?...
• 1x CR2032 battery holder https://www.aliexpress.com/item/32967379770.html?...
• 1x A string for the necklace

Required tools

• A soldering iron https://www.aliexpress.com/item/1995827068.html?s...
• Tweezers https://www.aliexpress.com/item/32858975688.html?...
• Soldering tin

Optional tools

• Soldering flux https://www.aliexpress.com/item/32865943785.html?...
• Multimeter https://www.aliexpress.com/item/32900257549.html?...
• A vice or a 3rd hand https://www.aliexpress.com/item/32800146519.html?...
• Acétone and an old toothbrush to clean the PCB

I'm a beginner in CAO but this sketch is pretty easy to do using Fusion 360.

I used the polygon tool and the circular pattern to draw this.

Between picture 1 and 2, I used a tool called Trim for the first time, it helped me cutting the extra lines.

When this was done, I right clicked on the sketch and clicked on "Save as DXF".

If you want to change the logo inside the PCB, draw your design using Fusion360 or Inkscape and export it as a .dxf file. After that, you can import it on the F.Silks layer on Kicad.

To turn a component footprint differently (either horizontally or vertically), click on the "e" key of your keyboard and point at it at the same time. After that, go to the tab called "Orientation" and specify the angle.

Below, you will find a .rar file gathering three folders. One contains all the pdf layers another contains gerber files and the last one contains the project.

The file you have available here contains some improvements compared to the initial file :

• I moved all the vias into the pad to make them invisible
• I moved the R1 footprint because I noticed that it made it harder to remove the battery

If you want to make the same design, just drag and drop all the gerber files on the website of your favorite PCB manufacturer (like JLCPCB or PCBWay). You can keep all the preconfigured parameters if you want but of course you can also change the PCB color.

This is probably the most boring part but it's necessary if you don't want to burn the eyes of people who look at the necklace ^^.

Determining the right luminosity of a particular LED color is pretty experimental.

To calculate the right value of the LED resistor, I used this method :

• I checked the voltage of the LED using the LED mode of my multimeter (In picture 2 we can see 2.571V for the blue LED)
• I did the test for the 5 LED colors I had and I determined that taking 2mA was a good value to start with
• Calculation : R = (Ubat - Uled)/A
  • For the blue LED, this formula gave me R=(3-2.571)/0.002 = 214.5 Ohms, the nearest value I had on my book was 220 Ohms so I picked 220 Ohms (See below for all the colors)
• I did a test, soldered the resistor to the LED, soldered 2 wires and powered that to the battery. If the luminosity is too strong for you, you can increase the resistor's value, if the light is too dim, decrease the value.

Blue : Uled = 2.571V and R=220 Ohms

White : Uled = 2.614V and R=200 Ohms

Green : Uled = 2.313V and R=360 Ohms

Orange : Uled = 1.887V and R=560 Ohms

Red : Uled = 1.790V and R=620 Ohms

Now it's time to solder everything.

Start soldering the 6 resistors. To make things easier you can add some flux if you have some.

If you want a multicolor necklace, don't forget to use the appropriate resistor for the LED.

If you have flux, add it on the 2 pads then place the battery holder and keep it in position by pressing on it with the tweezers.

This is the visible side of the PCB so you need to place the LEDs right on their footprints.

The positive voltage is outside the pendant and the negative voltage is inside.

In this case, my LED had one green end which represented the negative voltage.

Once all the soldering steps are done, you need to clean the PCB.

I used some acetone and an old toothbrush to clean. Please wear the appropriate safety equipment to handle acetone.

The last step is to insert the CR2032 battery when you want to light up the necklace. If you want to turn off the light, just unplug the battery.

Now feel free to make different pendants, enjoy mixing colors !

Also (and you will find this very convenient), it is now impossible to lose someone -human or animal- in the dark using this flashy necklace. I have tried with Baba chasing a cat and I could follow the whole scene.

If you make your own unique design, I would love to see it so don't forget to share it in comment ^^.

Have a nice day !