Smart home hardware is often expensive and locked down. I wanted to prove that you can build a transparent, robust, and fully local sensor for a fraction of the commercial price.
I recently challenged myself to build a robust, "Made in Quebec" smart thermometer. The goal? It had to be cheap ($9), fast to assemble (20 minutes), and open source. The result is a device I now use everywhere—from monitoring outdoor Canadian winters to checking inside deep freezers.
The Hardware: Simplicity is Key
Commercial sensors are often locked down or require expensive hubs. For this project, I went back to basics with readily available, high-reliability components.
Bill of Materials:
- The Brains: Wemos D1 Mini (ESP8266) - Tiny, cheap, and WiFi-native.
- The Sensor: Waterproof DS18B20 stainless steel probe. Indestructible and accurate.
- Power: Standard USB charger block.
Total Cost: Approximately $9 USD.
The "Secret Sauce": AI-Driven Development
I am a developer, but I didn't want to spend hours looking up datasheets. I used Claude AI as my hardware consultant and firmware engineer.
- Component Selection: Claude recommended the DS18B20 for its digital accuracy and waterproof characteristics.
- Firmware Generation: The AI generated 90% of the C++ code for the ESP8266, handling the tricky parts of WiFi management and sensor logic.
Features & Tech Specs
Despite the low price, the software stack is premium:
- Zero-Code Setup: Plug it in, and it creates a WiFi Access Point. Connect to it to select your home network—no hardcoding credentials!
- Modern Web UI: Accessible via any browser
http://IP_ADDRESS. Shows temperature in Celsius/Fahrenheit with a clean design. - Developer Friendly:
- REST API: Returns data in JSON format for easy integration.
- Home Assistant: Native integration support.
Open Source & Community
I believe in the right to repair and build. Ideally, technology should be accessible, not a black box.
I have open-sourced the entire project firmware. Whether you are a home automation enthusiast or just want to track your beer fridge temperature, you can use this code as a base.
👉 Get the Code on GitHub: augustose/D1-Temperature
What's Next?
I have units running stably in harsh environments right now. The satisfaction of seeing a "Made in Quebec" device appear in my Home Assistant dashboard—built with my own hands for pennies—is unbeatable.
Have you built your own sensors? Let me know on Twitter or grab the code and try it this weekend.