Incandescent Heartbeat

What Is It?

Incandescent lightbulbs have largely fallen out of favor these days, but some are still available for niche applications. This is what’s called an “appliance bulb”, meaning that it’s designed to last longer at the expense of poor quality light. This makes sense for bulbs in places that are hard to reach but not critical for viewing.

The Crafts Side

After some rough sketches, I settled on a design in which each half of the heart would be a power rail holding one of the two modules. The 555 was chosen for the positive side because it had more connections to power, and vice-versa for the shift register. Each module was tested independently before unifying them in order to more easily isolate faults. Thankfully, aside from some bridged pins on the 555 there were no issues.

In order to ensure the strongest possible connections, a liberal application of flux was used to ensure a full chemical bond between the conductors. The lid of a peanut butter jar was used as a platform. It was tall enough to conceal the 4 AAA batteries that power the sculpture as well as the power switch.

The Technology Side

The circuit uses the classic 555 timer to create a timing signal. This signal is fed into a binary counter circuit that counts from zero to eight. Bits 0 and 2 are passed into an AND gate formed from two NPN transistors. This gate is used to activate the bulb when the counter is equal to 1 or 3, leaving it off for the other 6 values. The transistors provide the added benefit of insulating the ICs from the relatively large current draw of the bulb. The whole arrangement is run at 6V from a pack of 4 AA batteries.