# 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)

---

## 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

---

## 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)

---

## 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)

---

## ESPHome Configuration Template

```yaml
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:
```

---

## 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

---

## 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

---

## 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

---

## 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

---

## References

- [ESP32-WROOM-32E Datasheet](https://www.espressif.com/sites/default/files/documentation/esp32-wroom-32e_esp32-wroom-32ue_datasheet_en.pdf)
- [TXB0104 Datasheet](https://www.ti.com/lit/ds/symlink/txb0104.pdf)
- [ESPHome Midea Component](https://esphome.io/components/climate/midea/)
- [ESPHome BLE Beacon](https://esphome.io/components/esp32_ble_beacon.html)
- [KiCad ESP32 Footprints](https://github.com/KiCad/kicad-footprints)

---

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