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The original SmartAC project used an ESP8266 to report room temperature, a Sonoff POW switch to control AC power, and a server-backed system that accepted Alexa commands. Its code remains online, but it is an old reference project—not a current, complete build guide. For most window units with a remote, an infrared (IR) controller is a safer retrofit than switching compressor power directly.
What the original SmartAC project did
Aleks Azen’s Hackster project treated a window air conditioner as a DIY smart thermostat: measure room temperature, decide whether cooling is wanted, and let a user issue voice commands. The author described high summer electricity bills as motivation, but the project page does not report controlled before-and-after measurements, so it does not establish energy savings. Hackster’s project account identifies an ESP8266, a Sonoff POW switch, server logic, and Alexa commands. The associated public code repository describes itself as the SmartAC backend.
The documented arrangement is best understood as separate sensing, decision, and control functions. The published ESP8266 sketch reads a temperature sensor and sends values over MQTT; it is not, on its own, complete AC-switching firmware. The project’s Alexa connection is described at the system level, but the available project account does not establish which Alexa skill or API it used.
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteDS18B20 temperature sensor → ESP8266 → MQTT → backend
↙ ↘
AC control path Alexa commands
The diagram shows the project’s broad roles, not a verified wiring schematic. The Hackster account does not provide a complete bill of materials or wiring instructions.
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What the published code confirms
The repository’s temperature.ino sketch uses the ESP8266 Wi-Fi library, PubSubClient for MQTT, and OneWire/DallasTemperature libraries for a DS18B20 sensor. In that sketch, the one-wire bus is assigned to D7; readings are published in Fahrenheit to b/temperature every 300000 milliseconds (five minutes), and the sketch subscribes to b/freq to allow the interval to be changed. It connects to an MQTT server on port 1811. The code rejects the DS18B20 readings 85.0 °C and -127.0 °C as errors.
Those are settings in the published sketch, not proof that a deployed system used identical production settings or that a five-minute interval is right for every room. GPIO labels also vary by ESP8266 board: verify the selected board’s pin mapping rather than assuming that a printed D7 label means the same physical connection on every module.
The AcController repository includes an index.js backend file and a README describing the project as the SmartAC backend, with sensitive data replaced by generic strings. The repository is sparse and does not provide a maintained, end-to-end setup. Treat it as historical code to inspect and adapt, not as firmware or a service to deploy unchanged. Replace placeholder configuration, use authenticated MQTT, and review the backend before exposing any control service.
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- Product Usage Instructions: Breez Max connects to a 2.4 GHz Wi-Fi network. It is compatible with any mini-split, window or portable unit that has an IR remote control. If your device doesn't work out of the box, please contact Cielo Customer Support to make it compatible. Breez Max has built-in temperature & humidity sensors that can be calibrated using the app. If the touch buttons don’t respond, press the temperature up & down buttons simultaneously to unlock the touch controls. For optimal placement and control, place Breez Max within 6-12 feet and in the line of sight of your air conditioner.
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- DIY Easy Set-Up: With an auto-detection algorithm for universal compatibility, Cielo Breez Max digital thermostat for mini-split can detect any air conditioner brand and model automatically! The smart air conditioner controller is compatible with over 20,000 models of mini-splits, window, or portable units.
- Comfy Max: With the AI-based Comfy Max ensure your AC only runs when it needs to, preventing overcooling and overheating. With a true thermostat like experience, always keep your home comfy and guarantee energy savings.
- Weekly Scheduling & Presets: Set one-time or repeat schedules for your air conditioner based on your routine. Your schedules will continue running smoothly even if internet connectivity is lost. Enjoy a truly tailored experience with predefined comfort settings including Home, Away, and Sleep.
Choose how the AC will be controlled before buying parts
The right method depends on the AC’s controls and how much access you need. Prefer the least invasive option that provides the required functions.
| Method | Best fit | Benefit | Main limitation |
|---|---|---|---|
| IR emitter | An AC with a remote | Usually avoids opening the appliance and can send power, mode, fan, or temperature settings when the remote protocol supports them. | Needs a usable signal path. Many remotes transmit a complete state, and manual remote use can leave the controller’s assumed state wrong. |
| Isolated button emulation | A digital-panel AC without a usable IR option | Can simulate controls without switching compressor current. | Requires opening the appliance and identifying the button circuit; it may not be isolated from mains. |
| Power switching | A unit that safely resumes the intended operation after power is restored, using properly rated appliance-control equipment | Can provide simple on/off control. | Compressor startup current, short cycling, power-restoration behavior, and mains installation all require careful assessment. |
A smart plug is not automatically suitable because its headline current rating may describe a resistive load rather than a compressor or motor load. Check the exact device rating, AC nameplate, manufacturer guidance, and local electrical requirements. A unit that does not resume cooling after power returns may also be a poor candidate for power switching.
Plan a safer modern retrofit
1. Check the AC’s behavior and controls
- Find out whether it has an IR remote, an electronic panel, or mechanical controls.
- Test what happens after a normal power interruption: does it return to the same mode and temperature, remain off, or require a button press?
- Decide whether you need only on/off or also mode, fan, and temperature control.
- Read the AC manufacturer’s instructions for external controls and restart behavior before designing around power interruption.
2. Build the low-voltage sensing and network path
A DS18B20 is a direct match for the original project. Wire it to the chosen ESP8266 board’s one-wire pin and include the pull-up resistor required by the sensor circuit. Mount it where it measures occupied-room air: away from the cold-air outlet, direct sun, compressor heat, and the ESP8266 regulator. Publish readings to a local, authenticated MQTT broker or a hub; do not reuse the old sketch’s generic configuration as credentials.
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- Super Easy Set-Up: Cielo Breez Lite is compatible with 20,000+ ductless mini-split, window, or portable AC and heat pump models. It automatically detects your remote control and is super easy to configure. It just takes a minute to set up. No tools required. For optimal placement and control, place Breez Lite within 6-12 feet and in the line of sight of your air conditioner.
- More Options, Better Control: Talk to your air conditioner using Google Assistant, Amazon Alexa, and Siri shortcuts. Cielo Breez Lite is also compatible with SmartThings and IFTTT!
- Enhanced Comfort & Savings: Designed to prioritize energy savings without compromising your comfort. Cielo Breez Lite smart air conditioner controller is loaded with next-gen features to help you save on heating and cooling bills.
- Perfect Temperature Always: Built-in temperature and humidity sensors, in combination with smart features, ensure perfect room temperature. You can always set intelligent triggers for an automated home climate.
Keep sensing and AC actuation as distinct functions. Confirm that readings arrive reliably and that sensor disconnection or invalid data is detected before enabling automatic cooling. A modern controller should have a defined response to sensor failure, such as refusing to start cooling automatically rather than treating an invalid value as a real temperature.
3. Add temperature hysteresis and restart protection
Do not switch at a single threshold: small temperature fluctuations can cause rapid on/off commands. Set an upper threshold for requesting cooling and a lower threshold for requesting it to stop. Add a minimum compressor off-time before restart, following the AC manufacturer’s instructions or advice from a qualified HVAC/electrical professional; there is no one delay that is right for every unit.
if sensor_valid is false:
do not start cooling automatically
if compressor_restart_is_not_permitted:
block the start request
if temperature >= cooling_on_threshold:
request cooling
if temperature <= cooling_off_threshold:
request off
Track desired state separately from the last command sent. This matters when an IR transmission is missed, someone uses the original remote, or the controller reboots without knowing the AC’s actual state.
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4. Implement the selected control method
- IR: Capture commands from the original remote and determine whether each transmission contains a complete AC state. Drive the IR LED through a suitable driver rather than directly from an ESP8266 GPIO. Test individual settings and provide a way to resynchronize after manual remote use.
- Button emulation: Unplug the AC before inspecting it. Use service information and a meter to identify contacts, confirm circuit voltage and isolation, then use a suitable optocoupler or signal relay to make short, debounced button pulses. Stop if the circuit’s safety cannot be established.
- Mains power switching: This is not a breadboard project. Equipment must be selected for the actual motor/compressor load and inrush, not just the running current. Enclosure, terminal ratings, isolation, conductor separation, grounding, strain relief, and overcurrent protection matter. Have a qualified professional assess the installation if you are not equipped to do that work safely.
Connect the controller to Alexa
The historical project account says Alexa commands were added to the server-backed system and refers to the AC as “wind” in the project video. It does not establish whether that integration used a custom skill, an official smart-home skill, or another intermediary. Do not assume the old code can be discovered by a current Alexa setup without additional work.
For a new build, choose an integration architecture based on the desired balance of local control and setup effort:
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- Local hub with MQTT: A platform such as Home Assistant can coordinate sensor readings, schedules, hysteresis, and device state locally, then expose controls to Alexa through a configured integration. A broker such as Eclipse Mosquitto can provide MQTT messaging but must be configured securely.
- Device emulation: Can be a short route to basic on/off voice control, but device semantics and compatibility may be limited or change over time.
- Cloud bridge or custom Alexa integration: Can support remote access or a tailored voice interface, at the cost of more configuration and dependence on accounts, internet service, and the integration provider. Alexa developer resources are at Amazon Alexa developer.
First verify control locally through the ESP8266’s own interface, MQTT, or hub. Add Alexa only after commands and reported state behave correctly without voice control. Use the Arduino IDE if it fits your firmware workflow, and consult the ESP8266 product information for the board platform. The original sensor choice is documented by the DS18B20’s manufacturer at Analog Devices.
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- AHR Product of the Year Smart Thermostat for Room Air Conditioners: Make your mini-split, window, or portable air conditioners smart (that come with an IR remote). Control your AC from anywhere using your phone or like a thermostat using on-device buttons with the award-winning smart thermostat for mini-splits.
- DIY Easy Set-Up: With an auto-detection algorithm for universal compatibility, Cielo Breez Max digital thermostat for mini split can detect any air conditioner brand and model automatically! The smart air conditioner controller is compatible with over 20,000 models of mini-splits, window, or portable units.
- Comfy Max: With the AI-based Comfy Max ensure your AC only runs when it needs to, preventing overcooling and overheating. With a true thermostat like experience, always keep your home comfy and guarantee energy savings.
- Weekly Scheduling & Presets: Set one-time or repeat schedules for your air conditioner based on your routine. Your schedules will continue running smoothly even if internet connectivity is lost. Enjoy a truly tailored experience with predefined comfort settings including Home, Away, and Sleep.
Test recovery, not just the happy path
Test the system locally and supervise an entire cooling cycle before relying on automation. Include failures that can create unsafe or surprising behavior:
- ESP8266 reboot, Wi-Fi loss, MQTT broker outage, and router reboot.
- Sensor disconnection and invalid readings, including the error values handled by the original sketch.
- Repeated Alexa commands, manual use of the AC remote or panel, and AC power loss and restoration.
- Missed IR transmission, incorrect button pulse, or a relay that operates but does not produce the expected AC response.
- Compressor restart timing and any unexpected ESP8266 resets when the compressor starts.
Prefer conservative recovery: after reboot or network restoration, do not unexpectedly start the compressor merely because an old command was replayed. If an ESP8266 resets when the compressor starts, or wiring becomes hot, arcs, buzzes, or behaves erratically, stop testing and address the power, interference, isolation, or installation problem before continuing.
When a different solution makes more sense
If the goal is voice control rather than an electronics project, a manufacturer-supported connected AC or a purpose-built IR controller may be more practical than opening the appliance. A smart plug is suitable only where the AC manufacturer permits the operating pattern, the unit resumes to the desired state, and the switch is rated for the actual compressor load. For a DIY build that needs room-temperature automation as well as voice commands, an IR-based controller paired with a local hub is usually the least invasive starting point.
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