Step 2: The CSS555 Micropower Timer IC
The heart of this novelty is the CSS555 timer integrated circuit. It is a micropower version of the venerable 555 and 7555 chips that the electronics world knows and loves. It has the exact same pin configuration and functions the same way. It actually can be user-programmed to work in various modes, but for the project described here, it is used in the standard 555 mode as it comes from the factory. Its key feature for the paperweight is the tiny amount of power that it needs to function. In this application, the circuit takes only about 6uA to carry out its timing tasks. The biggest current draw occurs when it blinks the LED which is only about 1/2% of the time. Thus on average, the circuit uses a tiny amount of power. This enables the paperweight to blink all night long on the energy it stores in its supercapacitor via a solar cell during the day or under your desk lamp.