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Introduction

Overview of KiCad as a PCB Design Tool​

KiCad is a powerful open-source software suite for electronic design automation (EDA). It is widely used for creating schematics and printed circuit board (PCB) layouts. With its robust set of tools, KiCad allows engineers and hobbyists to design complex PCBs, from simple single-layer boards to advanced multi-layer designs. The software supports a wide range of features, including schematic capture, PCB layout, 3D visualization, and generation of manufacturing files. KiCad is particularly popular in the maker and IoT communities due to its flexibility, cost-effectiveness, and active development community.

In this tutorial, we will explore the capabilities of KiCad 7 by designing a fully functional IoT device based on the ESP32 microcontroller. The project will cover the entire design workflow, from initial specification to generating manufacturing files.

Project Overview: ESP32-Based IoT Device​

The goal of this project is to design a general-purpose IoT device centered around the ESP32 WROOM module. The ESP32 is a versatile microcontroller with built-in Wi-Fi and Bluetooth capabilities, making it an ideal choice for IoT applications. The device will include a variety of features to demonstrate the flexibility of the ESP32 and the power of KiCad for PCB design.

The key functionalities of the IoT device include:

  • ESP32 WROOM Module: The core of the device, responsible for processing and connectivity.
  • SI7021 I²C Temperature and Humidity Sensor: Provides environmental sensing capabilities.
  • USB-to-Serial Programming Interface (CP2104): Enables easy programming and debugging of the ESP32.
  • RGB LED and Button Interface: Allows user interaction and status indication.
  • Level-Converted Outputs for LED Strips: Supports controlling external LED strips with 5V logic levels.
  • Fused Power Supply with Screw Terminals: Ensures safe and reliable power delivery.
  • Power Relay: Enables control of high-power devices.
  • Mounting Holes: Facilitates easy installation of the board.

Key Features of the IoT Device​

The IoT device is designed to be a versatile platform for various applications. Below is a detailed breakdown of its key features:

  1. ESP32 WROOM Module:

    • The ESP32 is the heart of the device, providing Wi-Fi and Bluetooth connectivity.
    • It is a low-cost, low-power microcontroller with a dual-core processor, making it suitable for IoT applications.

  2. SI7021 I²C Temperature and Humidity Sensor:

    • This sensor provides accurate environmental data, which can be used for monitoring and control applications.
    • It communicates with the ESP32 via the I²C bus, making it easy to integrate into the design.

  3. USB-to-Serial Programming Interface (CP2104):

    • The CP2104 chip enables programming and debugging of the ESP32 via a USB connection.
    • It also provides a serial communication interface for data exchange with a computer.

  4. RGB LED and Button Interface:

    • An RGB LED is included for visual feedback, such as indicating device status or errors.
    • A button interface allows users to interact with the device, such as resetting it or triggering specific actions.

  5. Level-Converted Outputs for LED Strips:

    • The device includes a level shifter (74HCT245) to convert the ESP32's 3.3V logic levels to 5V, enabling control of external LED strips.
    • This feature is useful for lighting applications or visual effects.

  6. Fused Power Supply with Screw Terminals:

    • The power supply circuit includes a fuse for overcurrent protection, ensuring the safety of the device.
    • Screw terminals provide a convenient way to connect external power sources.

  7. Power Relay:

    • A relay is included to control high-power devices, such as lights or motors.
    • The relay is driven by a transistor, which is controlled by the ESP32.

  8. Mounting Holes:

    • The board includes 3.2mm mounting holes in each corner, making it easy to install in enclosures or other fixtures.

Board Specifications​

The IoT device is designed to be compact and functional, with the following specifications:

  • Board Size: 80mm x 80mm (square).
  • Layer Count: 4-layer PCB.
    • Top Layer: Signal routing and component placement.
    • Inner Layer 1: Ground plane for noise reduction.
    • Inner Layer 2: Power plane for stable power distribution.
    • Bottom Layer: Signal routing and additional component placement.
  • Power Supply: 5V input via USB or screw terminals.
  • Operating Voltage: 3.3V for the ESP32 and peripherals.
  • Communication Interfaces: USB, I²C, and GPIO for external devices.

Tutorial Objectives​

By the end of this tutorial, you will:

  • Gain a solid understanding of the KiCad 7 workflow, from schematic design to PCB layout.
  • Learn how to design a 4-layer PCB with a focus on signal integrity and power distribution.
  • Understand how to integrate common IoT components, such as sensors, relays, and level shifters, into a PCB design.
  • Be able to generate manufacturing files (Gerber and drill files) for professional PCB production.
  • Develop the skills to troubleshoot and optimize your PCB designs.

Prerequisites​

To follow this tutorial, you should have:

  • Basic knowledge of electronics and PCB design concepts.
  • KiCad 7 installed on your computer (available for free from the official KiCad website).
  • Familiarity with the ESP32 microcontroller and its peripherals.
  • A willingness to learn and experiment with new tools and techniques.

This chapter sets the stage for the rest of the tutorial by introducing KiCad, outlining the project goals, and detailing the key features of the IoT device. With this foundation, you are now ready to dive into the schematic design process in the next chapter.