Love Spark is a heart shaped pendant that blinks an LED every three seconds and that time is based off of a research conducted by Amy Witter at the University of Melbourne concluding that people think of their friends & loved ones, on average, every 3 seconds. So it's not all just a fancy, blinky-blinly pendant. Every time that LED blinks, it reminds you how often you're thought of by the people who love you and that's a special feeling. Also, it's an excellent conversation starter!

Don't think I could have cooked up a better Valentine's day present for her in over a weekend.

Very minimum parts used, programmed using Arduino, the code looks simpler than Blink!

Parts required:

1. ATtiny13 (replaceable with a Tiny25/45/85)
2. Red SMD LED (1206/0805)
3. 3V button cell (1220/1225)
4. Cell holder (I made it myself)
5. Dual layer copper clad (preferably fiberglass)
6. SMD STDP switch (KPS-1290)
7. Some craft skills + patience
8. A valentine
9. Lots of love

The last three parts are priceless, the rest cost me roughly 300 INR (US$5)

Step 1: Cutting the PCB

1. Print the template, pick a desirable pendant size and cut it out
2. Trace the board outline from the cutout
3. Cut out the board with a fine hacksaw or a wire saw
4. Finish off the outline into nice and rounded edges with some files.

Step 2: Etching the PCB

I masked the PCB using toner transfer method on one side and permanent marker on the other side and etched using Ferric Chloride solution.

You can find the PCB template in the Download link on the last step, download it and laser print it. For the rest of the how-to, there are tons of articles on the internet and nice instructables on how to etch PCBs at home, most of those articles do a better job of explaining the process than I ever could.

This Two sided PCB using toner method by jmengel does a good job at explaining too.

Step 3: Finishing Touches

I'm not a big fan of the yellowish color of etched PCBs, I did some searching on how to color home made PCBs painlessly and came across this nice article. He uses fabric dye, given my laziness, I used some black hair dye, boiled the PCB in the dye-water mix for about 10 mins and the PCB was transformed!

Make sure your PCB traces are tinned before you dunk it in the hot dye mix.

Program the ATtiny, solder all components and you're good to go!

This is my third prototype. The first one, I tried to etch one side without masking the other side of the PCB and you know, there was noting left of it. The second one, I messed up the switch circuit and soldered the Tiny wrong way, really really stupid mistakes. The third one, the most beautiful etch in my DIY history, it was all worth it.

In all, It cost me four LEDs, three microcontrollers, three switches, FeCl2 stains on my shirt and a weekend hidden away in my workroom, she better like it!

In case you're wondering why cute hair. ;)

DIY files: DOWNLAOD

And for all you lazy, impatient and non-hackers, Kitables is making a Love Spark DIY kit that you can buy from here.