ESP_Midea/DESIGN_SPEC.md

Custom PCB Design Specification: Midea AC Controller with BLE Beacon

Recommended ESP Module

🏆 Best Choice: ESP32-WROOM-32E or ESP32-WROOM-32

Why ESP32 (not ESP8266 or ESP32-C6)?

• ✅ Bluetooth BLE Support: Required for beacon functionality
• ✅ Midea Component Compatibility: Works with Arduino framework (ESP32-C6 uses ESP-IDF, incompatible)
• ✅ Excellent ESPHome Support: Most mature and well-documented
• ✅ Dual Core: Can handle WiFi + BLE + Midea communication simultaneously
• ✅ Multiple UARTs: Can use hardware UART for Midea, software UART for debugging
• ✅ Good Memory: 520KB SRAM, sufficient for both features

Module Options

Module	Size	Flash	RAM	Price	Recommendation
ESP32-WROOM-32E	18×25.5mm	4MB	520KB	$$	⭐ Best for custom PCB
ESP32-WROOM-32	18×25.5mm	4MB	520KB	$$	⭐ Good alternative
ESP32-MINI-1	13.2×16.6mm	4MB	520KB	$$	Compact option
ESP32-C3	18×25.5mm	4MB	400KB	$	RISC-V, less support
ESP32-C6	18×25.5mm	4MB	512KB	$$	ESP-IDF only, no Midea

Recommended: ESP32-WROOM-32E (most common, best support)

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PCB Design Requirements

Core Components

1. ESP32-WROOM-32E Module

   • 38 pins (19 per side)
   • Requires 3.3V power
   • Built-in antenna

2. Logic Level Shifter (3.3V ↔ 5V)

   • TXB0104 (4-channel) or 74LVC245 (8-channel)
   • Required for Midea AC communication (5V logic)
   • Bidirectional for TX/RX

3. Power Supply

   • AMS1117-3.3 or LD1117-3.3 (3.3V regulator)
   • Input: 5V (USB or external)
   • Output: 3.3V @ 1A (ESP32 needs ~500mA peak)
   • Decoupling capacitors: 10µF + 100nF

4. USB-to-Serial (Optional but Recommended)

   • CP2102 or CH340C for programming/debugging
   • Allows OTA updates via USB
   • Auto-reset circuit for easy flashing

5. Midea AC Connector

   • JST-XH 4-pin or USB Type-A (depending on AC dongle)
   • Pins: VCC (5V), GND, TX, RX

6. Status LEDs

   • Power LED (3.3V)
   • WiFi status LED
   • BLE status LED (optional)
   • Midea communication LED (optional)

7. Reset Button

   • Reset ESP32
   • Boot button (GPIO0) for flashing

Pin Assignment

ESP32-WROOM-32E Pinout

Power:
  VDD (Pin 1, 3, 14, 21, 22, 27, 28, 33, 42) → 3.3V
  GND (Pin 2, 4, 13, 15, 20, 23, 26, 29, 34, 38, 40) → GND

Midea UART (via Level Shifter):
  GPIO17 (TX) → Level Shifter LV1 → HV1 → AC Dongle RX
  GPIO16 (RX) → Level Shifter LV2 → HV2 → AC Dongle TX
  GND → AC Dongle GND

USB-to-Serial (if included):
  GPIO1 (TX) → CP2102 RX
  GPIO3 (RX) → CP2102 TX
  GPIO0 (Boot) → CP2102 DTR (auto-reset)

Status LEDs:
  GPIO2 → WiFi Status LED
  GPIO4 → BLE Status LED (optional)
  GPIO5 → Midea Communication LED (optional)

Buttons:
  GPIO0 → Boot/Flash Button
  EN → Reset Button

Bluetooth:
  Built-in (no external pins needed)

Schematic Design

Power Section

USB 5V → AMS1117-3.3 → 3.3V → ESP32 VDD
                    ↓
                  GND → Common Ground

Midea Communication Section

ESP32 GPIO17 (TX) → TXB0104 LV1 → HV1 → AC Dongle RX
ESP32 GPIO16 (RX) → TXB0104 LV2 → HV2 → AC Dongle TX
ESP32 GND → TXB0104 GND → AC Dongle GND
ESP32 3.3V → TXB0104 LV
External 5V → TXB0104 HV → AC Dongle VCC (if needed)

Level Shifter Configuration (TXB0104)

• VCCA (LV): 3.3V from ESP32
• VCCB (HV): 5V from USB or external
• OE (Output Enable): Connect to 3.3V (always enabled)
• A1 (LV1): ESP32 GPIO17 (TX)
• B1 (HV1): AC Dongle RX
• A2 (LV2): ESP32 GPIO16 (RX)
• B2 (HV2): AC Dongle TX

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PCB Layout Considerations

Layer Stackup (2-layer minimum, 4-layer recommended)

2-Layer:

• Top: Components, signal traces
• Bottom: Ground plane, power traces

4-Layer (Recommended):

• Top: Components, signal traces
• Layer 2: Ground plane
• Layer 3: Power plane (3.3V)
• Bottom: Ground plane, remaining signals

Design Rules

1. Power Traces

   • 3.3V: Minimum 0.5mm (20mil) width
   • 5V: Minimum 0.5mm (20mil) width
   • GND: Use ground planes where possible

2. Signal Traces

   • UART: 0.2mm (8mil) minimum
   • Keep UART traces short (<50mm)
   • Avoid crossing power traces

3. Component Placement

   • ESP32 module: Center of board
   • Level shifter: Close to ESP32 and AC connector
   • Power regulator: Near USB input
   • Decoupling caps: Close to power pins (<5mm)

4. Antenna Clearance

   • Keep 15mm clearance around ESP32 antenna area
   • No ground plane under antenna
   • No components or traces near antenna

5. Thermal Considerations

   • Add thermal vias under power regulator
   • Ensure adequate copper for heat dissipation

Board Size Recommendation

• Minimum: 40mm × 50mm (fits ESP32 + essential components)
• Recommended: 50mm × 60mm (comfortable spacing, room for connectors)
• With USB: 50mm × 70mm (includes USB connector)

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Bill of Materials (BOM)

Essential Components

Component	Part Number	Quantity	Notes
ESP32 Module	ESP32-WROOM-32E	1	4MB flash, built-in antenna
Level Shifter	TXB0104PWR	1	4-channel, TSSOP-14
3.3V Regulator	AMS1117-3.3	1	SOT-223 or SOT-89
USB-to-Serial	CP2102N	1	Optional, QFN-24
USB Connector	USB-B Micro	1	Optional, for programming
AC Connector	JST-XH 4-pin	1	Or USB Type-A female
Reset Button	Tactile Switch	1	6×6mm
Boot Button	Tactile Switch	1	6×6mm (optional)
Status LED	LED 0603	2-3	Red/Green/Blue
Resistors	10kΩ 0603	2	Pull-up for buttons
Resistors	220Ω 0603	2-3	LED current limiting
Capacitors	10µF 0805	2	Power decoupling
Capacitors	100nF 0603	5-10	Decoupling

Optional Components

• BLE Status LED: Additional LED for Bluetooth status
• Midea Status LED: LED to show AC communication
• Crystal: 32.768kHz (if using RTC features)
• EEPROM: For storing settings (ESP32 has built-in)

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ESPHome Configuration Template

esphome:
  name: midea-ac-controller
  friendly_name: Midea AC Controller

esp32:
  board: esp32dev
  framework:
    type: arduino

# Enable logging (can use software serial or disable)
logger:
  baud_rate: 115200  # Or 0 to disable

# Enable Home Assistant API
api:
  encryption:
    key: !secret api_encryption_key

ota:
  - platform: esphome
    password: !secret ota_password

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password
  min_auth_mode: WPA2
  ap:
    ssid: "Midea AC Controller"
    password: !secret fallback_password

captive_portal:

# Status LEDs
binary_sensor:
  - platform: status
    name: "WiFi Status"
    
output:
  - platform: gpio
    pin: GPIO2
    id: wifi_led
  - platform: gpio
    pin: GPIO4
    id: ble_led

light:
  - platform: monochromatic
    output: wifi_led
    name: "WiFi Status LED"
  - platform: monochromatic
    output: ble_led
    name: "BLE Status LED"

# UART for Midea AC communication
uart:
  id: uart_midea
  tx_pin: GPIO17
  rx_pin: GPIO16
  baud_rate: 9600
  stop_bits: 1
  data_bits: 8
  parity: NONE

# Midea AC Control
climate:
  - platform: midea
    name: "AC Controller"
    uart_id: uart_midea
    autoconf: true
    beeper: false
    period: 2s
    timeout: 5s
    num_attempts: 3
    supported_modes:
      - COOL
      - HEAT
      - DRY
      - FAN_ONLY
    supported_swing_modes:
      - VERTICAL
      - HORIZONTAL
      - BOTH
    supported_presets:
      - ECO
      - BOOST
      - SLEEP
    visual:
      min_temperature: 17 °C
      max_temperature: 30 °C
      temperature_step: 0.5 °C

# Bluetooth Low Energy Beacon
esp32_ble_beacon:
  type: iBeacon
  uuid: 'c29ce823-e67a-4e71-bff2-abaa32e77a98'  # Change to unique UUID
  major: 1
  minor: 1
  tx_power: 0dBm

# Beeper control switch
switch:
  - platform: template
    name: "AC Beeper"
    icon: "mdi:volume-source"
    optimistic: true
    turn_on_action:
      - midea_ac.beeper_on:
    turn_off_action:
      - midea_ac.beeper_off:

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Design Checklist

Schematic Design

• ESP32-WROOM-32E module placed
• Power supply circuit (5V → 3.3V)
• Logic level shifter (TXB0104) connected
• Midea AC connector (JST-XH or USB)
• USB-to-Serial (optional but recommended)
• Status LEDs with current limiting resistors
• Reset and Boot buttons
• Decoupling capacitors (10µF + 100nF per power pin)
• Pull-up resistors for buttons

PCB Layout

• ESP32 antenna clearance (15mm no-ground zone)
• Power traces adequate width (0.5mm minimum)
• Ground planes on bottom layer
• UART traces kept short and away from power
• Decoupling caps close to power pins
• Thermal vias under regulator
• Component labels and reference designators
• Test points for debugging

Testing

• Power supply verification (3.3V stable)
• ESP32 boot and WiFi connection
• UART communication test
• Logic level shifter functionality (3.3V ↔ 5V)
• Midea AC communication
• BLE beacon transmission
• OTA update capability

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Manufacturing Notes

PCB Specifications

• Layers: 2-layer minimum, 4-layer recommended
• Thickness: 1.6mm standard
• Copper Weight: 1oz (35µm)
• Surface Finish: HASL or ENIG (ENIG for better quality)
• Solder Mask: Green (standard) or custom color
• Silkscreen: White or black

Assembly

• Component Package: 0603 or 0805 (hand-solderable)
• ESP32 Module: Can be hand-soldered or reflow
• Level Shifter: TSSOP-14 (requires careful soldering or stencil)

Recommended PCB Manufacturers

• JLCPCB: Good for prototypes, low cost
• PCBWay: Good quality, reasonable price
• OSHPark: US-based, good for small batches

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Cost Estimation

PCB Only (10 pieces)

• 2-layer 50×60mm: ~$5-10
• 4-layer 50×60mm: ~$20-30

Components (per unit)

• ESP32-WROOM-32E: $2-3
• TXB0104: $0.50
• AMS1117-3.3: $0.20
• CP2102N: $1-2 (optional)
• Other components: $1-2
• Total per unit: ~$5-8

Total Cost (10 units)

• PCB: $10-30
• Components: $50-80
• Total: ~$60-110 for 10 units

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Next Steps

1. Create KiCad Schematic

   • Add ESP32-WROOM-32E module
   • Design power supply
   • Add level shifter circuit
   • Connect all components

2. Design PCB Layout

   • Place components
   • Route traces
   • Add ground planes
   • Verify design rules

3. Order Prototype

   • Generate Gerber files
   • Order PCBs (start with 5-10 pieces)
   • Order components
   • Assemble and test

4. Test and Iterate

   • Test power supply
   • Test ESP32 functionality
   • Test Midea communication
   • Test BLE beacon
   • Fix any issues

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References

• ESP32-WROOM-32E Datasheet
• TXB0104 Datasheet
• ESPHome Midea Component
• ESPHome BLE Beacon
• KiCad ESP32 Footprints

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Last Updated: December 2025
Design Status: Specification Complete - Ready for Schematic Design