74HC00 Quad-NAND Logic Oscillator

Two NAND gates, one resistor and one cap make a square-wave clock — a textbook intro to digital logic without a microcontroller.

Difficulty: Breadboard. Estimated build time: about 25 minutes. Estimated parts cost: about US$2.20. 6-part bill of materials with live supplier pricing. An oscillator built from two NAND gates inside a single 74HC00 quad-NAND IC, blinking an LED at a few hertz.