View Arduino Uno Circuit Diagram Background. It also explains the role of atmega328 block diagram. The arduino uno pinout guide includes information you need about the different pins of the arduino uno microcontroller and their uses:

Arduino Uno Smd Reference Design In Designspark Pcb Format
Arduino Uno Smd Reference Design In Designspark Pcb Format from www.rs-online.com
The customer must not rely on the absence or characteristics of any features or instructions marked reserved or undefined. arduino reserves these for future definition and shall have no responsibility. The ldr detects a light over certain intensity, the arduino will trigger the buzzer.when the intensity of light decreases, the buzzer is turned off. As shown in the diagram above (via the red traces), the pins related to the a/d the arduino board uses a buffer (the lmv358) to drive the led.

Arduino uno pinout for circuit diagrams using this board.

This shield can drive two stepper motors at the same time. A year ago i have made once the circuit design is completed, it's time to make the pcb. The customer must not rely on the absence or characteristics of any features or instructions marked reserved or undefined. arduino reserves these for future definition and shall have no responsibility. I used the jlcpcb website to make my prototype board.