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

At present the circuit is still a work in progress. It's assembled on a breadboard, which allows connections to be easily changed.

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.