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231 changes: 231 additions & 0 deletions docs/tutorials/arduino-uno-schematic.mdx
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---
title: Arduino Uno Schematic
description: Create a schematic-only Arduino Uno core with an ATmega328P, reset pull-up, oscillator, power rails, and the four main shield headers.
---

## 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.

import TscircuitIframe from "@site/src/components/TscircuitIframe"

<TscircuitIframe defaultView="schematic" code={`
const atmega328pPins = {
pin1: "RESET",
pin2: "PD0_RXD",
pin3: "PD1_TXD",
pin4: "PD2_D2",
pin5: "PD3_D3_PWM",
pin6: "PD4_D4",
pin7: "VCC",
pin8: "GND1",
pin9: "XTAL1",
pin10: "XTAL2",
pin11: "PD5_D5_PWM",
pin12: "PD6_D6_PWM",
pin13: "PD7_D7",
pin14: "PB0_D8",
pin15: "PB1_D9_PWM",
pin16: "PB2_D10_PWM",
pin17: "PB3_D11_MOSI",
pin18: "PB4_D12_MISO",
pin19: "PB5_D13_SCK",
pin20: "AVCC",
pin21: "AREF",
pin22: "GND2",
pin23: "PC0_A0",
pin24: "PC1_A1",
pin25: "PC2_A2",
pin26: "PC3_A3",
pin27: "PC4_A4_SDA",
pin28: "PC5_A5_SCL",
} as const

export default () => (
<board width="120mm" height="85mm" routingDisabled>
<chip
name="U1"
footprint="dip28_wide"
manufacturerPartNumber="ATMEGA328P-PU"
pinLabels={atmega328pPins}
schWidth="20mm"
schHeight="38mm"
schX={0}
schY={0}
schPinArrangement={{
leftSide: {
direction: "top-to-bottom",
pins: [
"RESET",
"PD0_RXD",
"PD1_TXD",
"PD2_D2",
"PD3_D3_PWM",
"PD4_D4",
"PD5_D5_PWM",
"PD6_D6_PWM",
"PD7_D7",
"XTAL1",
"XTAL2",
],
},
rightSide: {
direction: "top-to-bottom",
pins: [
"VCC",
"AVCC",
"AREF",
"GND1",
"GND2",
"PB5_D13_SCK",
"PB4_D12_MISO",
"PB3_D11_MOSI",
"PB2_D10_PWM",
"PB1_D9_PWM",
"PB0_D8",
"PC5_A5_SCL",
"PC4_A4_SDA",
"PC3_A3",
"PC2_A2",
"PC1_A1",
"PC0_A0",
],
},
}}
/>

<pinheader
name="J1"
pinCount={8}
footprint="pinrow8"
gender="female"
pinLabels={["D0_RX", "D1_TX", "D2", "D3_PWM", "D4", "D5_PWM", "D6_PWM", "D7"]}
schX={-32}
schY={12}
schFacingDirection="right"
/>
<pinheader
name="J2"
pinCount={10}
footprint="pinrow10"
gender="female"
pinLabels={["SCL", "SDA", "AREF", "GND", "D13_SCK", "D12_MISO", "D11_MOSI", "D10_PWM", "D9_PWM", "D8"]}
schX={32}
schY={12}
schFacingDirection="left"
/>
<pinheader
name="J3"
pinCount={8}
footprint="pinrow8"
gender="female"
pinLabels={["IOREF", "RESET", "V3_3", "V5", "GND1", "GND2", "VIN", "NC"]}
schX={-32}
schY={-18}
schFacingDirection="right"
/>
<pinheader
name="J4"
pinCount={6}
footprint="pinrow6"
gender="female"
pinLabels={["A0", "A1", "A2", "A3", "A4_SDA", "A5_SCL"]}
schX={32}
schY={-18}
schFacingDirection="left"
/>

<resistor name="R1" resistance="10k" footprint="0603" schX={-16} schY={23} />
<crystal name="Y1" frequency="16MHz" loadCapacitance="22pF" footprint="hc49" schX={-17} schY={-9} />
<capacitor name="C1" capacitance="22pF" footprint="0603" schX={-23} schY={-13} />
<capacitor name="C2" capacitance="22pF" footprint="0603" schX={-11} schY={-13} />
<capacitor name="C3" capacitance="100nF" footprint="0603" schX={14} schY={22} />
<capacitor name="C4" capacitance="100nF" footprint="0603" schX={20} schY={22} />

<trace from="R1.pin1" to="net.V5" />
<trace from="R1.pin2" to="net.RESET" />
<trace from="U1.RESET" to="net.RESET" />
<trace from="J3.RESET" to="net.RESET" />

<trace from="U1.XTAL1" to="Y1.pin1" />
<trace from="U1.XTAL2" to="Y1.pin2" />
<trace from="Y1.pin1" to="C1.pin1" />
<trace from="Y1.pin2" to="C2.pin1" />
<trace from="C1.pin2" to="net.GND" />
<trace from="C2.pin2" to="net.GND" />

<trace from="U1.VCC" to="net.V5" />
<trace from="U1.AVCC" to="net.V5" />
<trace from="U1.GND1" to="net.GND" />
<trace from="U1.GND2" to="net.GND" />
<trace from="U1.AREF" to="J2.AREF" />
<trace from="C3.pin1" to="net.V5" />
<trace from="C3.pin2" to="net.GND" />
<trace from="C4.pin1" to="net.V5" />
<trace from="C4.pin2" to="net.GND" />

<trace from="J3.IOREF" to="net.V5" />
<trace from="J3.V5" to="net.V5" />
<trace from="J3.V3_3" to="net.V3_3" />
<trace from="J3.GND1" to="net.GND" />
<trace from="J3.GND2" to="net.GND" />
<trace from="J3.VIN" to="net.VIN" />
<trace from="J2.GND" to="net.GND" />

<trace from="U1.PD0_RXD" to="J1.D0_RX" />
<trace from="U1.PD1_TXD" to="J1.D1_TX" />
<trace from="U1.PD2_D2" to="J1.D2" />
<trace from="U1.PD3_D3_PWM" to="J1.D3_PWM" />
<trace from="U1.PD4_D4" to="J1.D4" />
<trace from="U1.PD5_D5_PWM" to="J1.D5_PWM" />
<trace from="U1.PD6_D6_PWM" to="J1.D6_PWM" />
<trace from="U1.PD7_D7" to="J1.D7" />

<trace from="U1.PB5_D13_SCK" to="J2.D13_SCK" />
<trace from="U1.PB4_D12_MISO" to="J2.D12_MISO" />
<trace from="U1.PB3_D11_MOSI" to="J2.D11_MOSI" />
<trace from="U1.PB2_D10_PWM" to="J2.D10_PWM" />
<trace from="U1.PB1_D9_PWM" to="J2.D9_PWM" />
<trace from="U1.PB0_D8" to="J2.D8" />
<trace from="U1.PC4_A4_SDA" to="J2.SDA" />
<trace from="U1.PC5_A5_SCL" to="J2.SCL" />

<trace from="U1.PC0_A0" to="J4.A0" />
<trace from="U1.PC1_A1" to="J4.A1" />
<trace from="U1.PC2_A2" to="J4.A2" />
<trace from="U1.PC3_A3" to="J4.A3" />
<trace from="U1.PC4_A4_SDA" to="J4.A4_SDA" />
<trace from="U1.PC5_A5_SCL" to="J4.A5_SCL" />
</board>
)
`} />

## 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.