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Tutorials

Arduino Uno Schematic

Overview​

This tutorial builds the schematic portion of an Arduino Uno-style board. It focuses on the ATmega328P core, reset pull-up resistor, clock circuit, and the four main headers that make the board compatible with Arduino shields.

Header Layout​

The four headers mirror the groups used on an Arduino Uno:

  • J1 carries digital pins D0-D7.
  • J2 carries SCL, SDA, AREF, ground, and digital pins D8-D13.
  • J3 carries IOREF, reset, 3.3 V, 5 V, ground, VIN, and one no-connect slot.
  • J4 carries analog pins A0-A5.

Keeping those groups separate makes the schematic easier to compare with the physical shield-header layout.

Reset And Clock​

R1 is the 10 kOhm pull-up that holds RESET high during normal operation. The reset header pin and the ATmega328P reset pin both share net.RESET, so adding a button or programming connector later only requires tying into that same net.

The 16 MHz crystal uses two 22 pF load capacitors to ground. The tutorial also adds two 100 nF decoupling capacitors for the VCC and AVCC pins.

Extending The Schematic​

This schematic intentionally stops before the USB interface, regulator, and auto-reset circuit. To keep building toward a complete Uno, add the USB-to-serial interface on D0_RX and D1_TX, route the power input through a regulator, and connect the reset net to the USB serial DTR signal through a small capacitor.