Note: You didn't provide the original article text, but since you requested a demonstration of specific Markdown capabilities and provided a very common technical project title, I have synthesized a comprehensive rewrite based on the standard technical process for this specific project (using an ESP8266 and the CN105 port). This allows me to showcase every requested feature while maintaining the "nuance" of a typical DIY home automation blog post.

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Project Log: Bringing a "Dumb" Mitsubishi AC into the Home Assistant Ecosystem

For years, I’ve lived with a Mitsubishi air conditioner that is, for lack of a better term, completely braindead. It works perfectly—cooling my room with clinical efficiency—but it lacks any form of network connectivity. No Wi-Fi, no app, just a plastic infrared remote that I constantly misplace. I considered buying a fancy IR blaster, but I wanted something more robust: true bidirectional communication.

I wanted to know the actual set point and the real-time return temperature, not just a "guessed" state based on the last IR command sent.

🛠️ The Blueprint

The secret lies in the CN105 port, a proprietary 5-pin connector found on most Mitsubishi indoor units. By interfacing an ESP8266 with this port, we can "speak" the AC's native language.

The Shopping List

• ESP8266 (NodeMCU or Wemos D1 Mini)
• 2x 10k $\Omega$ Resistors (for the voltage divider)
• Jumper wires and a soldering iron
• A 5-pin connector (or just some steady hands and thin wire)

🔌 Hardware Integration

The CN105 port uses a logic level that is not directly compatible with the ESP8266's 3.3V pins. To avoid frying my microcontroller, I had to implement a simple voltage divider.

Wiring Schematic:

Pro Tip: Be extremely careful when opening the AC chassis. The plastic clips are brittle, and one wrong move can lead to a permanent "gap" in your wall unit's aesthetic.

📉 System Architecture

The data flow is straightforward but powerful. The ESP8266 acts as the translator between the serial protocol of the AC and the MQTT/API protocol of Home Assistant.

💻 The Software Layer

I opted for ESPHome because it integrates natively with Home Assistant. The configuration is surprisingly lean. I used the mitsubishi_ac platform to handle the heavy lifting.

# Example ESPHome Configuration
climate:
  - platform: mitsubishi_ac
    name: "Bedroom AC"
    temperature_sensor: "bedroom_ac_temp"
    # The UART pins must match the wiring table above
    uart_id: uart_bus

uart:
  id: uart_bus
  tx_pin: GPIO13
  rx_pin: GPIO12
  baud_rate: 2400

To get this running, I had to:

1. Flash the ESP8266 via USB.
2. Define the climate entity in the YAML.
3. Reboot and let Home Assistant auto-discover the device.

🌡️ Calculating Efficiency

One of the best parts of having this data is calculating the actual thermal delta. I can now track how quickly the room cools using the formula for temperature change over time:

$\Delta T = T_{initial} - T_{final}$

If I want to calculate the approximate energy cost based on the compressor's runtime, I use: $\text{Cost} = \left( \frac{\text{Watts} \times \text{Hours}}{1000} \right) \times \text{Rate per kWh}$

🏁 Final Results & Reflections

The result is a seamless integration. I no longer hunt for the remote; instead, I have a beautiful climate card on my dashboard.

• Latency: Almost zero.
• Reliability: 100% (since it's wired, not IR).
• Satisfaction: Extremely high.

Status: Fully Automated ✅

I've realized that most "smart" appliances are just "dumb" appliances with a cheap Wi-Fi chip glued to the board. By adding my own, I've created a system that is actually smarter and more integrated than the official Mitsubishi Wi-Fi adapters.