Ken writes, “How do you make an LED blink? A vintage way is the LM3909, a chip from 1975 that can flash an LED for a year from a single flashlight battery. This chip has some surprising features, such as a charge pump that lets you power a 2-volt LED from a 1.5-volt battery. This IC was designed for simplicity, using just an LED, external capacitor, and battery. In this blog post, I reverse-engineer its silicon die.”
More details on Ken Shirriff’s blog.