Saturday, April 30, 2011

Show Love in a Heartbeat

I wanted to show my appreciation for the patience my girlfriend has with me when I'm hooked on a new project, so I decided to dedicate a project to her. Well she also pushed me a little bit by buying a small plastic heart and telling me to create something for her for a change :).

This could be a perfect gift for your loved one as well.

You need the following parts:

  • transparent and hollow heart shaped object 
  • 2 x red LEDs
  • 2 x 100kΩ resistors
  • 2 x 470Ω resistors
  • 2 x 100μF capacitors
  • 2 x NPN transistors (BC547)
  • 9V Battery with connector
  • transparent layer as a circuit board
I wanted a thin transparent circuit board so I took a transparent plastic sheet cut out of a grocery box. You can take anything you like but you may want to make sure that is transparent to let the whole heart glow in the front and in the back. After cutting it to the heart shape of the container object the fun part begins. Make the required holes for the components in your circuit board and assemble the cicuit in the following way:


Since I used a plastic layer, I had to be very careful to not melt it with my soldering iron. Due to the limited space I had on my circuit board, I had to assemble the circuit on both sides and had to place the capacitors on opposing sides. My finished circuit looked like this:

The red LEDs are already diffused, but still you would only see two dots blinking in the dark. To diffuse the light even more, you can fill your heart shaped container with a thin layer of soft tissue. The heart container I had wasn't big enough to hold my 9V battery block so I cut a small hole at the top to let out the connector wires.

As a last step I attached the 9V battery block at the back of the heart with some tape and connected it to the heart. When everything is finished it looks like this:

You can see that the load and unload cycles of the capacitors produce a heartbeat like effect.


  1. If you could find a way to fit the battery inside, it would make a good necklace.

  2. Actually if bend a capacitor hard enough it would fit but you always could use smaller batteries and maybe adjust the circuit. A necklace was my idea also, but the container is a bit big to wear around the neck. Right now it hangs at the window right in front of my girlfriend's workstation.