Hey Everyone, so here's something cool.

A PCB Necklace or Pendant powered by an Attiny13A.

The goal here was simple, to make a small Blinky board that can be attached to a chain so we can wear it like a locket or pendant.

There are a total of 24 LEDs in this Pendant, I've divided LEDs into pairs of 4.

This means 6 LEDs are connected in parallel and they are driven by a single AO3400 N channel mosfet. there are a total of 4 of these which control 6 LED segments each.

These 4 MOSFETs are then controlled by an Attiny13A, I've added a button with its D4 Pin which starts the LED sequence.

Material Required

• 0603 Blue LEDs x24
• Custom PCB which was provided by PCBWAY
• Attiny13A
• AO3400 N channel mosfet x4
• 10K 0603 Resistor x4
• SMD Coin Cell holder CR2032

Preparing the Board

I've prepared this PCB in the shape of a tear which I first modeled in Tinkercad.

After preparing the Basic shape, I exported it into fusion360 so I could export the DXF file from it as my OrCad PCB Suit only imports the DXF file for making PCB Layer.

After importing the Tear Shape in my PCB suite, I prepared the Board Schematic first that consists of an Attiny13A driving four different N-channel mosfet setup which is then connected to a total of 24 LEDs.

After finalizing the schematic, I exported the netlist and prepared the PCB by using the imported Tear shape as a reference.

Getting PCBs from PCBWAY

After completing the design, I uploaded the Gerber data on PCBWAY's quote page, I selected the solder mask color which was RED, and placed the order.

After placing the order, I received the PCBs in a week and the PCB quality was pretty great.

This shape is completely random so it's pretty hard to make but they did an awesome job of making this PCB with no error whatsoever.

You guys can check out PCBWAY If you want Great PCB Service at an Affordable rate and low price.

ASSEMBLY PROCESS

After unboxing the PCBs, I started the assembly process which had the following steps.

• Solder Paste Dispensing
• Pick & Place Process
• Hotplate Reflow
• LED Testing
• Adding Coin Cell holder
• Programming

Solder paste Dispensing

The first step is to apply solder paste to each component pad.

I used a normal Sn-Pb solder paste which has a melting temp from 140 to 270 °C.

After Adding solder paste, we move on to the next process which is the "PICK & Place Process"

PICK & Place Process

I then used an ESD Tweeaser to carefully pick and place each component on their assigned place one by one which took like 30 Seconds tops but the result was a perfect PCB with all the components placed in their location.

Hotplate Reflow

After the "PICK & Place Process", I carefully lifted the whole circuit board and place it on my DIY SMT Hotplate which is also homemade just like this project.

After a Few mins when the hotplate reaches the Solderpaste melting TEMP, all the components will get soldered by this Hot Reflow process.

We then remove the PCB from the Hotplate to cool down all componenets and board surface.

Testing LEDs Continuity

Because we are using LEDs here, it's crucial to check whether LEDs are soldered properly or not.

I used a normal Multimeter set in Diode checking mode, we connect the probe of the multimeter to the Anode and Cathode of leds in right polarity.

If LEDs are soldered properly, all LEDs will glow. If there's any soldering error they won't glow.

Coin Cell Holder

After testing the LEDs, we move on to the next step which is to add a Coin cell holder to the bottom layer of the PCB.

After this the board is almost completed, now we just have to flash the Attiny13A with the main sketch.

Programming

This is the code that I have used in this project, it's a simple Chaser sketch that toggles each Mosfet in a chaser sequence.

const int switchPin = 4; 
int pinsCount=4;                       
int pins[] = {3,2,1,0};   
int lightMode = 1; 

void setup() 
{
    pinMode(0, OUTPUT);
    pinMode(1, OUTPUT);
    pinMode(2, OUTPUT);
    pinMode(3, OUTPUT);
    pinMode(switchPin, INPUT_PULLUP);
   digitalWrite(0, LOW);
   digitalWrite(1, LOW);
   digitalWrite(2, LOW);
   digitalWrite(3, LOW);
     
}
void loop()
{ 
    if (digitalRead(switchPin) ==LOW) 
    { 
        lightMode = lightMode + 1;
        if (lightMode == 3)
        {
            lightMode = 1;
        }
    }
    if (lightMode == 1)
    {
        digitalWrite(pins[0,1,2,3], LOW);
        delay(200);
    }
    else if (lightMode == 2)
    {
      for (int i=0; i<pinsCount; i=i+1){    // chasing right
      digitalWrite(pins[i], HIGH);         // switching the LED at index i on
      delay(70);                          // stopping the program for 100 milliseconds
      digitalWrite(pins[i], LOW);          // switching the LED at index i off
    }
      for (int i=pinsCount-1; i>0; i=i-1){   // chasing left (except the outer leds)
      digitalWrite(pins[i], HIGH);         // switching the LED at index i on
      delay(70);                          // stopping the program for 100 milliseconds
      digitalWrite(pins[i], LOW);          // switching the LED at index i off
     }
    }
        
    //delay(200); // see text
}

As for Flashing the Attiny13A, I'm using one of my previous projects which was this Attiny Programmer made from an Arduino nano.

Checkout More from

Basically, we use this SOIC8 Clip to hold the Attiny13A from the TOP side and flash it with Arduino IDE.

Powering the Locket/Pendant

To Power this setup, I've added a CR2032 Coin Cell holder which we can use to power the Attiny13 and LEDs.

I've not calculated the exact backup of each cell but its more than 12 Hours

Adding Chain

Now because this setup is a Pendant or a locket or a necklace whatever we might call this, it needs a chain or something that we can attach to its provided hole so we can wear it like normal jewelry.

We can add it to a chain or even convert it into earrings by adding an earpiece hook with the provided hole on the PCB.

Result

This is the end result of this build, a small wearable pendant or a necklace that is a perfect gift item for this upcoming valentine's day.

Special thanks to PCBWAY for supporting this project, checkout PCBWAY for getting great PCB service at less cost.

Thanks again and I'll be back with a new project soon!

Peace