Nest thermostats are certainly popular, and are likely one of the most influential products in the still-burgeoning internet of things market. The technology in a Nest, however, is actually pretty straightforward. It can be programmed for heating and cooling schedules, is smart enough to adapt to your use, and can be remotely controlled. But, Nest thermostats are overpriced at more than $200. For just 1/20th of that cost, you can create your own DIY smart thermostat.
This hack comes to us from Mat at Not Enough Tech, and relies on the Sonoff Basichome automation device. The Sonoff device is essentially just an ESP8266 with a relay added, and it can be used to wirelessly control whatever you want, just like you would with any other IoT device. It only costs $5, so even with another $5 spent on the DHT11 temperature sensor, your total cost should only be $10.
Most basic thermostats work exactly the same: the have either a mechanical or digital means of determining the temperature, and then they toggle your HVAC system when it surpasses what you have set. There are usually just 3 wires running from the thermostat to your HVAC, with one for ground, one for mains power, and one for signal. When the signal wire and live wire are connected, the HVAC turns on — easy enough to do with a relay. However, it may be slightly more complicated if your thermostat controls the air conditioner as well.
To follow this guide, you’ll need to install the Tasmota firmware on your Sonoff device, which gives you more control over its functionality. Then connect the temperature sensor and the thermostat wires. Next, you can use Mat’s Node-RED to control the Sonoff relay, which switches the heater on or off in this case. All you need to do is set the temperature range you prefer, and the Sonoff will turn on your heater anytime it gets colder than that.