Arduino Uno Schematic

Overview

This tutorial builds a schematic-only Arduino Uno compatible board in tscircuit. The goal is not to route a PCB; it is to capture the recognizable functional blocks that make the Uno useful as a reference design:

• ATmega328P microcontroller core
• USB-UART bridge for programming and serial monitor access
• 5 V and 3.3 V power rails
• 16 MHz crystal and load capacitors
• reset pull-up, reset button, and auto-reset capacitor
• digital, analog, power, and ICSP headers
• built-in L LED on D13

Full Schematic Snippet

Use this snippet as a starting point for documentation, education, or a schematic-only compatibility reference. It keeps each block named clearly so you can replace the generic footprints with exact manufacturer parts later.

export default () => (
<board width="120mm" height="80mm" routingDisabled>
  <net name="VUSB" />
  <net name="V5" />
  <net name="V3_3" />
  <net name="VIN" />
  <net name="GND" />
  <net name="RESET" />
  <net name="AREF" />
  <net name="XTAL1" />
  <net name="XTAL2" />

  <chip
    name="U1"
    footprint="dip28"
    schWidth="34mm"
    schHeight="52mm"
    pinLabels={{
      pin1: "RESET",
      pin2: "D0_RX",
      pin3: "D1_TX",
      pin4: "D2",
      pin5: "D3_PWM",
      pin6: "D4",
      pin7: "VCC",
      pin8: "GND",
      pin9: "XTAL1",
      pin10: "XTAL2",
      pin11: "D5_PWM",
      pin12: "D6_PWM",
      pin13: "D7",
      pin14: "D8",
      pin15: "D9_PWM",
      pin16: "D10_PWM_SS",
      pin17: "D11_PWM_MOSI",
      pin18: "D12_MISO",
      pin19: "D13_SCK",
      pin20: "AVCC",
      pin21: "AREF",
      pin22: "AGND",
      pin23: "A0",
      pin24: "A1",
      pin25: "A2",
      pin26: "A3",
      pin27: "A4_SDA",
      pin28: "A5_SCL",
    }}
    schPinArrangement={{
      leftSide: {
        direction: "top-to-bottom",
        pins: [
          "RESET",
          "D0_RX",
          "D1_TX",
          "D2",
          "D3_PWM",
          "D4",
          "D5_PWM",
          "D6_PWM",
          "D7",
        ],
      },
      rightSide: {
        direction: "top-to-bottom",
        pins: [
          "D8",
          "D9_PWM",
          "D10_PWM_SS",
          "D11_PWM_MOSI",
          "D12_MISO",
          "D13_SCK",
          "A0",
          "A1",
          "A2",
          "A3",
          "A4_SDA",
          "A5_SCL",
        ],
      },
      topSide: {
        direction: "left-to-right",
        pins: ["VCC", "AVCC", "AREF"],
      },
      bottomSide: {
        direction: "left-to-right",
        pins: ["GND", "AGND", "XTAL1", "XTAL2"],
      },
    }}
    connections={{
      VCC: "net.V5",
      AVCC: "net.V5",
      GND: "net.GND",
      AGND: "net.GND",
      AREF: "net.AREF",
      RESET: "net.RESET",
      XTAL1: "net.XTAL1",
      XTAL2: "net.XTAL2",
      D0_RX: "net.D0_RX",
      D1_TX: "net.D1_TX",
      D2: "net.D2",
      D3_PWM: "net.D3_PWM",
      D4: "net.D4",
      D5_PWM: "net.D5_PWM",
      D6_PWM: "net.D6_PWM",
      D7: "net.D7",
      D8: "net.D8",
      D9_PWM: "net.D9_PWM",
      D10_PWM_SS: "net.D10_PWM_SS",
      D11_PWM_MOSI: "net.D11_PWM_MOSI",
      D12_MISO: "net.D12_MISO",
      D13_SCK: "net.D13_SCK",
      A0: "net.A0",
      A1: "net.A1",
      A2: "net.A2",
      A3: "net.A3",
      A4_SDA: "net.A4_SDA",
      A5_SCL: "net.A5_SCL",
    }}
  />

  <chip
    name="U2"
    footprint="soic16"
    schX={-38}
    schY={12}
    schWidth="26mm"
    schHeight="34mm"
    pinLabels={{
      pin1: "VCC",
      pin2: "GND",
      pin3: "TXD",
      pin4: "RXD",
      pin5: "DTR",
      pin6: "UD+",
      pin7: "UD-",
      pin8: "XI",
      pin9: "XO",
    }}
    schPinArrangement={{
      leftSide: {
        direction: "top-to-bottom",
        pins: ["UD+", "UD-", "DTR"],
      },
      rightSide: {
        direction: "top-to-bottom",
        pins: ["TXD", "RXD"],
      },
      topSide: {
        direction: "left-to-right",
        pins: ["VCC"],
      },
      bottomSide: {
        direction: "left-to-right",
        pins: ["GND", "XI", "XO"],
      },
    }}
    connections={{
      VCC: "net.V5",
      GND: "net.GND",
      TXD: "net.D0_RX",
      RXD: "net.D1_TX",
      DTR: "net.DTR",
      "UD+": "net.USB_D_PLUS",
      "UD-": "net.USB_D_MINUS",
    }}
  />

  <connector
    name="J_USB"
    standard="usb_c"
    schX={-68}
    schY={12}
    pinLabels={{
      pin1: "VBUS",
      pin2: "D-",
      pin3: "D+",
      pin4: "GND",
    }}
    connections={{
      VBUS: "net.VUSB",
      "D-": "net.USB_D_MINUS",
      "D+": "net.USB_D_PLUS",
      GND: "net.GND",
    }}
  />
  <fuse
    name="F_USB"
    footprint="0603"
    currentRating="500mA"
    voltageRating="6V"
    schX={-52}
    schY={2}
    connections={{ pin1: "net.VUSB", pin2: "net.V5" }}
  />

  <chip
    name="U3"
    footprint="sot223"
    schX={-36}
    schY={-26}
    pinLabels={{
      pin1: "GND",
      pin2: "VOUT",
      pin3: "VIN",
    }}
    connections={{
      VIN: "net.VIN",
      VOUT: "net.V5",
      GND: "net.GND",
    }}
  />

  <chip
    name="U4"
    footprint="sot23-5"
    schX={-12}
    schY={-26}
    pinLabels={{
      pin1: "VIN",
      pin2: "GND",
      pin3: "EN",
      pin4: "NC",
      pin5: "VOUT",
    }}
    connections={{
      VIN: "net.V5",
      VOUT: "net.V3_3",
      GND: "net.GND",
      EN: "net.V5",
    }}
  />

  <crystal
    name="Y1"
    frequency="16MHz"
    loadCapacitance="18pF"
    footprint="hc49"
    schX={2}
    schY={-32}
  />
  <capacitor
    name="C1"
    capacitance="22pF"
    footprint="0402"
    schX={-8}
    schY={-42}
    connections={{ pos: "net.XTAL1", neg: "net.GND" }}
  />
  <capacitor
    name="C2"
    capacitance="22pF"
    footprint="0402"
    schX={12}
    schY={-42}
    connections={{ pos: "net.XTAL2", neg: "net.GND" }}
  />

  <resistor
    name="R_RESET"
    resistance="10k"
    footprint="0402"
    schX={-16}
    schY={34}
    connections={{ pos: "net.V5", neg: "net.RESET" }}
  />
  <capacitor
    name="C_RESET"
    capacitance="100nF"
    footprint="0402"
    schX={-34}
    schY={30}
    connections={{ pos: "net.DTR", neg: "net.RESET" }}
  />
  <pushbutton
    name="SW_RESET"
    schX={-2}
    schY={34}
    connections={{ pin1: "net.RESET", pin2: "net.GND" }}
  />

  <led
    name="LED_L"
    color="yellow"
    footprint="0603"
    schX={30}
    schY={18}
  />
  <resistor
    name="R_L"
    resistance="1k"
    footprint="0402"
    schX={42}
    schY={18}
    connections={{ pos: "net.D13_SCK", neg: ".LED_L > .anode" }}
  />
  <trace from=".LED_L > .cathode" to="net.GND" />

  <connector
    name="J_DIGITAL_LOW"
    schX={52}
    schY={32}
    pinLabels={{
      pin1: "D0/RX",
      pin2: "D1/TX",
      pin3: "D2",
      pin4: "D3 PWM",
      pin5: "D4",
      pin6: "D5 PWM",
      pin7: "D6 PWM",
      pin8: "D7",
    }}
    connections={{
      "D0/RX": "net.D0_RX",
      "D1/TX": "net.D1_TX",
      D2: "net.D2",
      "D3 PWM": "net.D3_PWM",
      D4: "net.D4",
      "D5 PWM": "net.D5_PWM",
      "D6 PWM": "net.D6_PWM",
      D7: "net.D7",
    }}
  />
  <connector
    name="J_DIGITAL_HIGH"
    schX={52}
    schY={4}
    pinLabels={{
      pin1: "D8",
      pin2: "D9 PWM",
      pin3: "D10 PWM/SS",
      pin4: "D11 PWM/MOSI",
      pin5: "D12/MISO",
      pin6: "D13/SCK",
      pin7: "GND",
      pin8: "AREF",
      pin9: "SDA",
      pin10: "SCL",
    }}
    connections={{
      D8: "net.D8",
      "D9 PWM": "net.D9_PWM",
      "D10 PWM/SS": "net.D10_PWM_SS",
      "D11 PWM/MOSI": "net.D11_PWM_MOSI",
      "D12/MISO": "net.D12_MISO",
      "D13/SCK": "net.D13_SCK",
      GND: "net.GND",
      AREF: "net.AREF",
      SDA: "net.A4_SDA",
      SCL: "net.A5_SCL",
    }}
  />
  <connector
    name="J_ANALOG"
    schX={52}
    schY={-22}
    pinLabels={{
      pin1: "A0",
      pin2: "A1",
      pin3: "A2",
      pin4: "A3",
      pin5: "A4/SDA",
      pin6: "A5/SCL",
    }}
    connections={{
      A0: "net.A0",
      A1: "net.A1",
      A2: "net.A2",
      A3: "net.A3",
      "A4/SDA": "net.A4_SDA",
      "A5/SCL": "net.A5_SCL",
    }}
  />
  <connector
    name="J_POWER"
    schX={-62}
    schY={-24}
    pinLabels={{
      pin1: "RESET",
      pin2: "3V3",
      pin3: "5V",
      pin4: "GND",
      pin5: "GND",
      pin6: "VIN",
    }}
    connections={{
      RESET: "net.RESET",
      "3V3": "net.V3_3",
      "5V": "net.V5",
      GND: "net.GND",
      VIN: "net.VIN",
    }}
  />
  <connector
    name="J_ICSP"
    schX={26}
    schY={-34}
    pinLabels={{
      pin1: "MISO",
      pin2: "V5",
      pin3: "SCK",
      pin4: "MOSI",
      pin5: "RESET",
      pin6: "GND",
    }}
    connections={{
      MISO: "net.D12_MISO",
      V5: "net.V5",
      SCK: "net.D13_SCK",
      MOSI: "net.D11_PWM_MOSI",
      RESET: "net.RESET",
      GND: "net.GND",
    }}
  />

  <capacitor
    name="C_DECOUPLE_1"
    capacitance="100nF"
    footprint="0402"
    schX={-18}
    schY={-42}
    connections={{ pos: "net.V5", neg: "net.GND" }}
  />
  <capacitor
    name="C_DECOUPLE_2"
    capacitance="100nF"
    footprint="0402"
    schX={-28}
    schY={-42}
    connections={{ pos: "net.V5", neg: "net.GND" }}
  />
  <capacitor
    name="C_AREF"
    capacitance="100nF"
    footprint="0402"
    schX={24}
    schY={30}
    connections={{ pos: "net.AREF", neg: "net.GND" }}
  />

  <trace from=".Y1 > .pin1" to="net.XTAL1" />
  <trace from=".Y1 > .pin2" to="net.XTAL2" />
</board>
)

Block Notes

Microcontroller Core

The ATmega328P symbol groups user-facing GPIO on the left and right, then keeps power, reference, ground, and oscillator pins on the top and bottom. That makes the schematic easier to read than a strict DIP pin order while still preserving the Uno pin names.

USB-UART And Auto Reset

The USB connector feeds a small USB-UART bridge. The bridge TXD pin connects to D0_RX, RXD connects to D1_TX, and DTR passes through C_RESET to the RESET net. That auto-reset capacitor is what lets the bootloader reset when the serial port opens during upload.

Power Rails

VIN feeds a 5 V regulator, USB VBUS feeds the 5 V rail through F_USB, and the 5 V rail feeds a 3.3 V regulator. The schematic includes both rails on J_POWER, matching the mental model users expect from an Uno compatible board. Keep decoupling capacitors close to the microcontroller and regulator pins when you later convert this into a PCB.

Clock And Reset

The 16 MHz crystal uses two 22 pF load capacitors to ground. R_RESET pulls reset high, and SW_RESET pulls it low when pressed.

Headers

The headers expose the Uno-style groups:

• J_DIGITAL_LOW for D0 through D7
• J_DIGITAL_HIGH for D8 through D13, AREF, SDA, and SCL
• J_ANALOG for A0 through A5
• J_POWER for reset, power, and ground
• J_ICSP for SPI programming

Extending The Snippet

For a manufacturable Uno-compatible PCB, replace the generic footprints with the exact connectors, regulators, USB-UART bridge, and microcontroller package you plan to source. Then add PCB placement, keepouts, and routing constraints in a separate layout-focused tutorial or component.