Based on a budget WIFI module ESP8266 you can easily and quickly develop IoT devices. Examples of such devices can be wireless sensors of temperature, humidity, pressure, illumination. To do this, just update the firmware of the module and connect the corresponding sensors. Additional microcontrollers are not needed.
The firmware currently supports reading sensors DHT11/22 BMP085/180, BH1750, DS18B20, AM2321 and others. There is a function of transmitting testimonies to the site of popular monitoring, to the metering service ThingSpeak.com, MQTT server, to the MajorDoMo smart home system, to Benux computer control system. It is possible to control the state of free GPIOs to control loads (relays), read the status of GPIO inputs, display data on an LCD or OLED screen, and many other functions.
An example of a sensor connection scheme for evaluating the ease of assembly of a device is shown in Figure 1.
Figure 1 – An example of connecting sensors to ESP8266
The actual and correct connection diagram may differ (for example, it is advisable to supply 5V for the DHT22 sensor). It is also not recommended to use ESP-01. Recommended modules ESP-07 and ESP-12 and others, with the maximum derived GPIO. For a more complete use of the firmware, modules with a flash memory of 1 megabyte or more are recommended, a re-soldering of the memory chip is possible.
Let’s take a closer look at an example of connecting a company temperature sensor DALLAS DS18B20 (рис.2) to ESP8266 to create an IoT device Wi-Fi thermometer.
Figure 2 – Appearance of the sensor DS18B20
We connect power to the ESP8266. We also give a plus to the contact CH_PD. Attention! If you are not using ESP-01, you must file GPIO15 – GND; GPIO2 -3.3V. ESP-01 has already done this. We connect RX and TX to the USB-TTL converter for flashing and debugging the code (Fig. 3).
Figure 3 – ESP8266 firmware using a converter
We connect the DS18B20 to the ESP8266. If you look at the markings: left – ground, middle – signal (GPIO12 on ESP-03), if you have ESP-01, connect to GPIO0, right – power (3.3V). Between the power and the signal line, it is desirable to connect a 4.7 kOhm resistor (Fig. 4).
Figure 4 – Connection DS18B20 to ESP8266
Register at https://thingspeak.com/, create a channel, copy the 16-character key from there. We need it to send temperature data to the cloud.
firmware of NodeMCU
NodeMCU (https://github.com/nodemcu/nodemcu-firmware) – is a firmware that allows you to run Lua scripts on ESP8266. Download the latest NodeMCU Flasher (https://github.com/nodemcu/nodemcu-flasher) and run it.
Connect GPIO0 to ground. We select the desired COM port and the speed is 74880 or 115200. Press Flash and distort the power to the ESP8266. If the firmware does not start, we check the correctness of the RX, TX connection by starting PuTTY at a speed of 74880. At the moment of power supply to the console, a line like “
ets Jan 8 2013, rst cause: 1, boot mode: (1,0)“. After the correct firmware, disconnect GPIO0 from the ground.
Figure 5 – Firmware of ESP8266
Pouring Lua scripts and launch
Download and run LuaLoader (http://benlo.com/esp8266/index.html#LuaLoader). We select the COM port and speed 9600, if there is no connection, we try to distort the power supply of the ESP8266 module. Check the connection by clicking on the ChipID button. The chip identifier should be displayed in the console
We fill in the necessary files (button UploadFile):
1. ds18b20.lua – library for interacting with DS18B20;
2. httpsender.lua – our script that reads temperature data and sends it to thingspeak.com. Do not forget to replace YOURAPIKEY on your own key.
gpio = 6 – when connecting the sensor to GPIO12, in case GPIO0 – gpio = 3 (table – https://github.com/nodemcu/nodemcu-firmware/blob/master/README.md):
gpio = 6
-- conection to thingspeak.com
print("Sending data to thingspeak.com")
conn:on("receive", function(conn, payload)
-- api.thingspeak.com 22.214.171.124
conn:send("GET /update?key=YOURAPIKEY&field1="..t.." HTTP/1.1\r\n") conn:send("Host: api.thingspeak.com\r\n")
conn:send("User-Agent: Mozilla/4.0 (compatible; esp8266 Lua; Windows NT 5.1)\r\n")
-- send data every 60000 ms to thing speak
tmr.alarm(0, 60000, 1, function() sendData() end )
3. init.lua – script, initializes Wi-Fi and launches httpsender.lua. Do not forget to set your SSID and password for Wi-Fi:
print("Setting up WIFI...")
--modify according your wireless router settings wifi.sta.config("SSID","SSIDPASSWD")
tmr.alarm(1, 1000, 1, function()
if wifi.sta.getip()== nil then
print("IP unavaiable, Waiting...")
print("Config done, IP is "..wifi.sta.getip())
As result we have the following: