ESP_Midea/KICAD_GUIDE.md

KiCad Schematic and PCB Design Guide

Step-by-Step Schematic Creation

1. Component Libraries Setup

First, ensure you have the necessary libraries:

• ESP32-WROOM-32: ESP32 module footprint
• TXB0104: Logic level shifter
• AMS1117: Voltage regulator
• CP2102N: USB-to-Serial (optional)
• Standard libraries: Resistors, Capacitors, LEDs, Connectors

2. Schematic Components List

Add these components to your schematic:

Power Section

• U1: AMS1117-3.3 (Voltage Regulator)
• C1: 10µF Capacitor (Input)
• C2: 10µF Capacitor (Output)
• C3: 100nF Capacitor (Input decoupling)
• C4: 100nF Capacitor (Output decoupling)
• USB1: USB Micro-B Connector (Power input)

ESP32 Module

• U2: ESP32-WROOM-32E Module

Logic Level Shifter

• U3: TXB0104PWR (4-channel level shifter)

Midea AC Connector

• J1: JST-XH 4-pin Connector (or USB Type-A female)

USB-to-Serial (Optional)

• U4: CP2102N (USB-to-Serial converter)
• USB2: USB Micro-B Connector (Programming)

Status LEDs

• LED1: LED (WiFi Status) - GPIO2
• LED2: LED (BLE Status) - GPIO4
• R1: 220Ω Resistor (LED1 current limiting)
• R2: 220Ω Resistor (LED2 current limiting)

Buttons

• SW1: Tactile Switch (Reset)
• SW2: Tactile Switch (Boot/Flash)
• R3: 10kΩ Resistor (Reset pull-up)
• R4: 10kΩ Resistor (Boot pull-up)

Decoupling Capacitors

• C5-C10: 100nF Capacitors (ESP32 power pins)

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Detailed Schematic Connections

Power Supply Section

USB1 (Micro-B):
  Pin 1 (VCC) → C1+ → U1.IN
  Pin 1 (VCC) → C3+ → U1.IN
  Pin 4 (GND) → GND

U1 (AMS1117-3.3):
  IN → USB1.VCC (via C1, C3)
  GND → GND
  OUT → C2+ → 3V3 (Power Rail)
  OUT → C4+ → 3V3 (Power Rail)

Power Rails:
  3V3 → ESP32 VDD pins
  3V3 → Level Shifter VCCA
  3V3 → LED anodes (via resistors)
  3V3 → Button pull-ups
  GND → Common ground plane

ESP32-WROOM-32E Connections

U2 (ESP32-WROOM-32E):
  VDD (Pins: 1,3,14,21,22,27,28,33,42) → 3V3 (via decoupling caps)
  GND (Pins: 2,4,13,15,20,23,26,29,34,38,40) → GND
  
  GPIO17 (TX) → U3.A1 (Level Shifter LV side)
  GPIO16 (RX) → U3.A2 (Level Shifter LV side)
  
  GPIO2 → R1 → LED1 (WiFi Status)
  GPIO4 → R2 → LED2 (BLE Status)
  
  GPIO0 → SW2 (Boot Button) → GND
  GPIO0 → R4 → 3V3 (Pull-up)
  
  EN → SW1 (Reset Button) → GND
  EN → R3 → 3V3 (Pull-up)
  
  GPIO1 (TX) → U4.RXD (if USB-to-Serial included)
  GPIO3 (RX) → U4.TXD (if USB-to-Serial included)

Logic Level Shifter (TXB0104)

U3 (TXB0104PWR):
  VCCA → 3V3 (Low voltage side)
  VCCB → 5V (High voltage side - from USB or external)
  GND → GND
  OE → 3V3 (Always enabled)
  
  A1 (LV1) → U2.GPIO17 (ESP32 TX)
  B1 (HV1) → J1.RX (AC Dongle RX)
  
  A2 (LV2) → U2.GPIO16 (ESP32 RX)
  B2 (HV2) → J1.TX (AC Dongle TX)
  
  A3, A4, B3, B4 → NC (Not connected)

Midea AC Connector

J1 (JST-XH 4-pin or USB Type-A):
  Pin 1 (VCC) → 5V (if AC dongle needs power)
  Pin 2 (RX) → U3.B1 (Level Shifter HV1)
  Pin 3 (TX) → U3.B2 (Level Shifter HV2)
  Pin 4 (GND) → GND

USB-to-Serial (Optional)

U4 (CP2102N):
  VDD → 3V3
  GND → GND
  DTR → U2.GPIO0 (Auto-reset for flashing)
  RXD → U2.GPIO1 (ESP32 TX)
  TXD → U2.GPIO3 (ESP32 RX)
  VBUS → USB2.VCC (5V detection)

USB2 (Micro-B):
  VCC → U4.VBUS
  D+ → U4.D+
  D- → U4.D-
  GND → GND

Status LEDs

LED1 (WiFi Status):
  Anode → R1 → U2.GPIO2
  Cathode → GND

LED2 (BLE Status):
  Anode → R2 → U2.GPIO4
  Cathode → GND

Buttons

SW1 (Reset):
  Pin 1 → U2.EN
  Pin 2 → GND
  (R3 pull-up: U2.EN → 3V3)

SW2 (Boot):
  Pin 1 → U2.GPIO0
  Pin 2 → GND
  (R4 pull-up: U2.GPIO0 → 3V3)

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PCB Layout Guidelines

Component Placement Order

1. ESP32 Module (Center)

   • Place ESP32-WROOM-32E in center of board
   • Leave 15mm clearance around antenna area (top-right corner)
   • No ground plane under antenna

2. Power Section (Top Left)

   • USB connector near edge
   • AMS1117 regulator close to USB
   • Decoupling capacitors within 5mm of regulator

3. Level Shifter (Between ESP32 and AC Connector)

   • TXB0104 close to ESP32 GPIO17/GPIO16
   • Positioned to minimize trace length to AC connector

4. AC Connector (Right Edge)

   • JST-XH connector on right edge
   • Easy access for cable connection

5. USB-to-Serial (Bottom Left, Optional)

   • CP2102N and USB connector
   • Separate from power USB

6. Status LEDs (Top Edge)

   • Visible when board is mounted
   • Near board edge

7. Buttons (Accessible Location)

   • Reset and Boot buttons
   • Easy to press during development

Routing Priorities

1. Power Traces (Highest Priority)

   • 3V3: Minimum 0.5mm (20mil) width
   • 5V: Minimum 0.5mm (20mil) width
   • Use power planes if 4-layer board

2. Ground (Critical)

   • Ground plane on bottom layer
   • Connect all GND pins to plane
   • Keep ground continuous

3. UART Signals (High Priority)

   • Keep traces short (<50mm)
   • Avoid crossing power traces
   • Route together (differential pair style)
   • 0.2mm (8mil) minimum width

4. GPIO Signals (Standard)

   • 0.15mm (6mil) minimum width
   • Keep away from antenna area

Design Rules

• Trace Width:

  • Power: 0.5mm (20mil)
  • Signal: 0.15-0.2mm (6-8mil)

• Via Size:

  • Diameter: 0.5mm (20mil)
  • Drill: 0.2mm (8mil)

• Clearance:

  • Trace to trace: 0.15mm (6mil)
  • Trace to pad: 0.15mm (6mil)

• Antenna Keepout:

  • 15mm radius around ESP32 antenna
  • No ground plane
  • No components
  • No traces (except necessary)

Layer Stackup (2-Layer)

Top Layer:

• Components
• Signal traces
• Power traces (3V3, 5V)

Bottom Layer:

• Ground plane (primary)
• Power traces (if needed)
• Signal traces (minimal)

Layer Stackup (4-Layer Recommended)

Layer 1 (Top):

• Components
• Signal traces

Layer 2 (Inner 1):

• Ground plane

Layer 3 (Inner 2):

• Power plane (3V3)

Layer 4 (Bottom):

• Ground plane
• Signal traces

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KiCad Specific Instructions

1. Adding Components

1. Open KiCad Schematic Editor
2. Click "Place Symbol" (A key)
3. Search for components:
   • ESP32-WROOM-32E (may need to download footprint)
   • TXB0104 (may need custom symbol)
   • AMS1117 (search in library)
   • Standard: R, C, LED, SW_Push, Conn_01x04_Male

2. Creating Custom Symbols (if needed)

ESP32-WROOM-32E:

• Create new symbol in Symbol Editor
• Add pins according to ESP32-WROOM-32E datasheet
• Save to custom library

TXB0104:

• Create symbol with 14 pins (TSSOP-14)
• Pins: VCCA, A1-A4, GND, OE, B1-B4, VCCB, GND

3. Assigning Footprints

1. Open "Assign Footprints" tool
2. Assign footprints:
   • ESP32-WROOM-32E → ESP32-WROOM-32 footprint
   • TXB0104 → TSSOP-14 footprint
   • AMS1117 → SOT-223 or SOT-89 footprint
   • Resistors → R_0603 or R_0805
   • Capacitors → C_0603 or C_0805
   • LEDs → LED_0603
   • Buttons → SW_PUSH_6mm
   • Connectors → Appropriate JST or USB footprint

4. Netlist and PCB

1. Generate Netlist (F8)
2. Open PCB Editor
3. Read Netlist (F8 in PCB Editor)
4. Place components according to guidelines
5. Route traces following priorities

5. Design Rule Check (DRC)

1. Run DRC before finalizing
2. Check for:
   • Unconnected nets
   • Clearance violations
   • Trace width violations
   • Via size issues

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Component Footprint Reference

Component	Footprint	Package
ESP32-WROOM-32E	Custom/ESP32-WROOM-32	Module
TXB0104PWR	TSSOP-14	TSSOP
AMS1117-3.3	SOT-223	SOT-223
CP2102N	QFN-24	QFN
Resistors	R_0603 or R_0805	0603/0805
Capacitors	C_0603 or C_0805	0603/0805
LEDs	LED_0603	0603
Buttons	SW_PUSH_6mm	6×6mm
USB Micro-B	USB_Micro-B	Through-hole
JST-XH	JST_XH_B4B-XH-A	Through-hole

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Testing Checklist

After PCB assembly:

• Power supply: 3.3V stable at ESP32 VDD
• ESP32 boots (check serial output)
• WiFi connects
• BLE beacon transmits
• UART communication works
• Level shifter: 3.3V → 5V conversion verified
• Midea AC responds to commands
• Status LEDs function
• Buttons work (Reset, Boot)
• OTA updates work

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Common Issues and Solutions

Issue: ESP32 doesn't boot

• Check: Power supply voltage (should be 3.3V)
• Check: Decoupling capacitors
• Check: EN pin connection

Issue: UART communication fails

• Check: Level shifter connections
• Check: 5V power to level shifter VCCB
• Check: TX/RX not swapped

Issue: WiFi/BLE interference

• Check: Antenna clearance (15mm)
• Check: No ground plane under antenna
• Check: Component placement

Issue: Power regulator overheating

• Check: Adequate copper for heat dissipation
• Check: Thermal vias under regulator
• Check: Input voltage (should be 5V)

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Next Steps

1. Create Schematic following the connections above
2. Assign Footprints to all components
3. Generate Netlist and import to PCB
4. Place Components according to guidelines
5. Route Traces following priorities
6. Run DRC and fix any issues
7. Generate Gerbers for manufacturing
8. Order Prototype (start with 5-10 boards)

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Ready to start? Open KiCad and begin with the power supply section, then add ESP32, level shifter, and connectors.