This voltage-booster circuit for driving one or more white LEDs uses a 555 timer as its main element (see the figure). The timer, IC1, functions as a resettable astable multivibrator where R1, R2 ...

Enter the 555 Frank decided on the ever-so-handy 555 Timer IC, which was configured as an adjustable duty cycle square wave generator. Seen in the accompanying schematic, the 555 square wave generator ...

This gets its clock signal from a 555 timer circuit. [Andrea’s] schematic is a bit hard to read, but grab a copy, blow it up a bit (or use your browser zoom) and study the CD4017 datasheet (PDF ...