The Internet of Things, or IoT for short, focuses on the various ways in which devices can be connected to a network so that they can communicate with one another and send and receive data and commands. This is arguably the most important aspect of the IoT itself. There are already technologies like Bluetooth, WiFi, NFC, etc. that can help with last-mile connectivity, but most of them are hard to set up and often need extra hardware like a local control server or appliance. In this project, I show you how to build and set up a simple standalone board that, with the help of a wifi network, can send environmental data to the internet and receive commands to turn on/off a switch. This project, which costs less than 10 or 15 US dollars to build, does the following: Send readings from a DHT11 sensor about temperature and humidity to a MQTT broker and a Thingspeak channel. Listen for MQTT messages and use ESP8266 to turn on or off a relay.

Check a Thingspeak channel every so often, and if the field has changed, turn on or off a relay. In simple terms, this is a temperature/humidity sensor and relay that can connect to the internet. The relay can be used to turn on or off any AC appliance that is connected to it. The parts needed cost less than 15 US dollars, and you don't need any other hardware. All of the software used is open source, and to connect the board to the internet, only free online

services were used. It is assumed that there is a WiFi network that the board can connect to that works. Even though there are already a few projects that show how to set up an ESP8266 module to send data to the internet, I have not seen a solution that also lets you use the internet to control a device that is connected to the ESP8266 module. This project shows how simple it is to do that.

1. ESP8266 ESP-01 module 2. DHT11 or DHT22 sensor 3. 5v relay 4. LM1117 3.3v LDO voltage regulator 5. N2222A transistor 6. 1 x 470 uF capacitor 7. 2 x 10 uF Tantalum capacitor 8. 2 x 1K resistor

10. male breakaway headers 11. PCB Board 12. FTDI USB to TTL adapter cable

You can order the ESP8266 module, the DHT11/22 sensor, and the USB to TTL cable from ebay.com. Buying all three should not cost more than $9. The rest of the parts can be bought for a few dollars at any store that sells electronics. The ESP8266 module should be able to connect to a working WiFi access point and know how to log in to it. The circuit is pretty simple. The board

can be powered either by the USB cable alone or by a 5v DC supply plugged into the power socket at the top. A LM1117-3.3 LDO is used to give the ESP8266 module the 3.3v it needs. On the GPIO2 pin of the ESP8266, there is a DHT11 sensor. Depending on where the jumper is, the GPIO0 pin can be linked to either the ground or the relay. The temperature and humidity readings, as well as the relay state, are sent from the board to: MQTT broker: Any MQTT broker can be used (http://mqtt.org/). In my case, I used www.cloudmqtt.com, which has a free online broker. You'd need to make both an account and an instance. And put the details of the instance in the user config.h file. Using an online broker is helpful because you can access it from any network. If a local broker is used, like one that runs on a Raspberry Pi, it may be hard to connect to it from outside the home network because ISPs usually block incoming ports. Thingspeak.com: On Thingspeak.com, you need to set up an account. Also, a channel with these three channels needs to be made and the details of that

field1 - relay state field2 - temperature field3 - humidity Even though, in its current state, the board needs to be connected to both cloudmqtt and Thingspeak for all functions to work, the code can be easily changed to use only one of these options.