#149 — Voice Home Automation

Python speech recognition and a relay board — say "turn on lamp" and the relay clicks. No Alexa, no cloud, fully local.

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🧪 What Is It?

Alexa and Google Home are convenient but they send every word you say to corporate cloud servers. Build a voice-controlled home automation system that runs entirely on your local network. A Raspberry Pi with a USB microphone runs Vosk (offline speech recognition) — it listens for wake words and commands without ever connecting to the internet. When it hears "turn on the lamp," it triggers a relay that switches the lamp's power outlet. Add more relays for more devices: fan, heater, lights, TV, coffee maker. You get the convenience of voice control without the privacy invasion. Everything stays in your house.

🔨 Build Steps

1. Set up offline speech recognition. Install Vosk on the Pi: pip install vosk. Download a language model (English small model is ~50MB). Write a Python script that captures audio from the USB mic and feeds it through the Vosk recognizer. Test that it correctly transcribes speech without internet connection.
2. Define your command vocabulary. Create a dictionary of commands and their actions: "turn on lamp" -> relay 1 on, "turn off lamp" -> relay 1 off, "fan on" -> relay 2 on, etc. Keep commands short and distinct. Vosk can be configured with a limited vocabulary for better accuracy.
3. Implement wake word detection. Add a wake word ("Hey computer," "Hey house," or something custom) before commands are processed. The system ignores speech until the wake word is detected, then listens for a command within a 5-second window. This prevents accidental activations.
4. Wire the relay module. Connect relay control pins to the Pi's GPIO. Test each relay by toggling the GPIO pin — you should hear the relay click and see the LED indicator change. Keep the relay module close to the Pi for clean wiring.
5. Wire the relay to mains power. THIS IS THE DANGEROUS STEP. Wire each relay's normally-open contacts in series with one conductor (hot wire) of the device's power cord. When the relay closes, the circuit completes and the device powers on. Use a proper junction box and wire nuts. If you're uncomfortable with mains wiring, use relay-controlled smart plugs instead.
6. Add voice feedback. Install pyttsx3 (offline text-to-speech) and a speaker. The Pi confirms commands: "Turning on the lamp." "Fan is now off." Feedback confirms the system heard correctly before acting.
7. Add status tracking. Keep track of each relay's state (on/off). Respond to queries: "Is the lamp on?" -> "The lamp is currently on." Add a "turn off everything" command for convenience.
8. Build a web dashboard (optional). A Flask web app shows all devices and their states. Toggle devices from your phone on the local network as a backup to voice control.

⚠️ Safety Notes

• Relays switching mains voltage (120V/240V) can kill you. If you are not confident wiring mains electricity, use pre-made relay-controlled smart plugs instead of wiring directly into outlets. All mains wiring should be inside an approved junction box with proper strain relief.
• Never exceed the relay's current rating. A standard 10A relay can handle lamps and fans but NOT space heaters, air conditioners, or other high-draw appliances. Check the relay's rating and the device's current draw before connecting.
• The Pi and relay module must be kept away from water and mounted in a location where they won't be bumped or knocked into. A relay that's physically jostled while switching mains power is a shock and fire hazard.

🔗 See Also

• Sentiment Room Lighting
• Pi-hole Ad Blocker