Bare ATmega328P Blink

An Arduino Uno without the Uno — the bare AVR chip on a breadboard with crystal, decoupling, and an LED on PB5.

Difficulty: Through-hole. Estimated build time: about 60 minutes. Estimated parts cost: about US$6.00. 9-part bill of materials with live supplier pricing. The Arduino Uno is essentially an ATmega328P plus a USB-serial bridge plus a regulator.