Hearty is one of my earliest projects.

My design goal was to come up with the simplest possible circuit that did something interesting. I thought about this for a long time.

Eventually I settled on the effect of having an LED fade out smoothly using a capacitor on its anode. This produces a eerily organic-looking decay rate.

Then I realized I could use a vibration spring switch to trigger the effect. It’s just a very weak spring placed around a post in an airtight cylinder; when agitated the spring jangles against the post and closes the circuit. This is essentially a primitive accelerometer. This allowed the circuit to be triggered organically. It was magical how cool and organic it looked in contrast to how simple it actually was.

Eventually I figured out that you could use a much smaller capacitor by using it to drive a transitor.

The circuit is just one resistor, one transistor, one capacitor and the spring switch.

Due to its passive switch design it uses zero power when not activated, allowing the tiny CR1220 watch battery to last basically forever.

I couldn’t design on a physical form this circuit should be attached to. I thought about this for a long time.

Eventually it became pretty obvious that a heart with a red LED was an extremely natural and appealing choice.

I made a pixel-heart shape and put a lion’s face in the silkscreen art.

Eventually I decided to use a simplified medical drawing of a real heart on top of the pixel heart — still in white silkscreen art. The contrast between the medical drawing and the super abstract pixelized heart felt interesting.

Originally I just had a single old-fashioned 5mm through-hole LED in the center.

Eventually I realized I could make this using SMD components easily enough. By flipping the SMD LEDs upside down and hand-soldering them, I could have them shine through the PCB, for a really, really cool effect.

I was blown away by how cool it looked, despite it’s extreme design simplicity. A lot of other people liked it to. It took me several years to get from the basic conception to the finished design.

I’m still really happy with it. I like watching people play with it, and how much joy such a simple thing seems to give them.

It led me to all of my other designs, now with far more advanced accelerometers and microcontrollers. Everything I’ve done since is based around the same basic principles I learned from this project:

1. It should look beautiful even when it’s turned off
2. It should invoke some organic form rather than looking like a computer PCB
3. Extreme low power usage: the user should not have to think about turning it off or on
4. You should pick it up and it should respond to you instantly
5. You should know how to “use” it from the moment you pick it up. No features that have a learning curve.
6. Small, lightweight size
7. Low build cost
8. It should respond uniquely and organically, only when called up. It should not display a static pattern, which would get old quickly.