Home Automation with Alexa

31 31-03:00 dezembro 31-03:00 2020 — 1 Comentário

A few years ago, I have explored here, how to use Alexa, an intelligent personal assistant made popular by the Amazon Echo and Echo-Dot, in Home Automation projects:

When IoT Meets AI: Home Automation With Alexa and NodeMCU and

Alexa – NodeMCU: WeMo Emulation Made Simple

Alexa is capable of voice interaction, music playback, making to-do lists, setting alarms, streaming podcasts, playing audiobooks, and providing weather, traffic, and other real time information. Alexa can also control several smart devices using itself as a home automation hub. We will use on this project, the “Echo Dot”, that allows users to activate the device using a wake-word, such as “Alexa” or “Computer”, as in “Star Trek!.

In the home automation space, Alexa can interact with several different devices as Philips Hue, Belkin Wemo, Sonoff, etc. On previous projects, we emulated WeMo devices, using the fauxmoESP library, that seems to be outdated and not properly maintained nowadays. Here we will use Espalexa, an easy to use Arduino library compatible with both ESP8266 and ESP32.

The below block diagram shows what will be developed on our project:

The below video, shows how the project will look like at the end:

1. Bill of Material (BoM)

(All values are referenced in USD)

2. Install ESP boards

At Arduino IDE Preferences –> Additional boards Manager URLs enter with:

https://dl.espressif.com/dl/package_esp32_index.json, http://arduino.esp8266.com/stable/package_esp8266com_index.json

Next, at Arduino IDE Tools/Boards Manager, Install boards:

Boards Manager.png

On this project, we will use the NodeMCU, but the code could be easily adapted to also work with ESP32. So, let’s also install it:

Boards Manager.png

The ESP8266 NodeMCU Pinout:


3. The Espalexa Library

Espalexa allows you to set a ranged value (e.g. Brightness, Temperature) and optionally a color, additionally to standard on/off control. For example, you can say — “Alexa, turn the light to 75% “.

Espalexa emulates parts of the SSDP protocol and the Philips hue API, just enough so it can be discovered and controlled by Alexa.

By default, it’s possible to add up to a total of 10 devices because each device “slot” occupies memory, even if no device is initialized. You can change the maximum number of devices by adding for example:


before calling the library:

#include <Espalexa.h>

It is recommend setting MAXDEVICES to the exact number of devices you want to add to optimize memory usage.To install the library, go to Arduino IDE Tools/Manage Libraries, and enter with espalexa:

Library Manager.png

4. Home Automation prototype

Our Home Automation project will be created having 4 smart devices working that can be individually remotely controlled. But suppose that we want to group our devices to be used on our home. What should be done?

For example, suppose that our home has 2 rooms:

  • Bed Room
  • Living Room

Now, suppose that you want to have one lamp and one outlet in each room. So, let’s group our 4 devices as shown at the introduction block diagram:

Bed Room

  • Light 2
  • Outlet 1 (Fan)

Living Room

  • Light1
  • Outlet 2 (Buzzer)

Ou Home Automation Project will be more or less like this:

5. Assembling the HW for testing

For testing purposes, 4 color LEDs will be used as “IoT devices”. They should be installed as shown at diagram and listed below:

==> Red LED (Light1) ==> NodeMCU D1 (GPIO5) – Living Room

==> Green LED (Outlet1) ==> NodeMCU D2 (GPIO4) – Living Room

==> Blue LED (Light2) ==> NodeMCU D5 (GPIO14) – Bed Room

==> Yellow LED (Outlet2) ==> NodeMCU D6 (GPIO12) – Bed Room

The LEDs red and green, will simulate the devices to be installed on “Living Room” and LEDs blue and yellow will simulate the ones installed on “Bed Room”


6. Creating our IoT Devices on Arduino IDE

First, we must call the libraries:

#include <ESP8266WiFi.h>
#include <Espalexa.h>

Following for NodeMCU pins definitions to be connected to devices (at test phase will be LEDs and at final project, Relays inputs):

#define RelayPin1 5  //D1
#define RelayPin2 4  //D2
#define RelayPin3 14 //D5
#define RelayPin4 12 //D6

Once we have 4 devices, at least 4 direct callback functions should be defined:

void device1Changed(uint8_t brightness);
void device2Changed(uint8_t brightness);
void device3Changed(uint8_t brightness);
void device4Changed(uint8_t brightness);

The brightness parameter contains the new device state (0:off, 255:on, 1-254:dimmed) that will be sent by Alexa when that callback function is called.But the callback function can be in fact any function to be executed under Alexa command, so we will define here 3 additional special functions to be called that will handle multiple IoT devices:

void devFunc1Changed(uint8_t brightness);
void devFunc2Changed(uint8_t brightness);
void devFunc3Changed(uint8_t brightness);

The above callback functions will be associated to:

  • All Home Devices (Light1, Light2, Outlet1 and Outlet2)
  • Living Room (Light1 and Outlet1)
  • Bed Room (Light2 and Outlet2)

So, Alexa will in fact handle 7 “IoT devices”. For each one of them, we must define a unique name to be called by Alexa:

// device names
String Device_1_Name = "Red light";
String Device_2_Name = "Green light";
String Device_3_Name = "Blue light";
String Device_4_Name = "Yellow light";

// device_function names
String Dev_Func_1_Name = "Living Room";
String Dev_Func_2_Name = "Bed Room";
String Dev_Func_3_Name = "All Home Devices";

During testing phase, we will call the LEDs by “{its color} Light”. On our final project we can changed those variables by its final name (“Light 1”, “Outlet2”, etc).The last but not least, we should declare the variables to be used by espalexa:

Espalexa espalexa;

and for communication:

boolean connectWifi();
boolean wifiConnected = false;
const char* ssid = "YOUR SSID HERE";
const char* password = "YOUR PASSWORD HERE";

On Setup phase, you should besides the usual pin and serial bald-rate definitions and communication start procedures, have each one of the IoT devices with its name properly associated and espalexa started:

// Define your devices here.
espalexa.addDevice(Device_1_Name, device1Changed);
espalexa.addDevice(Device_2_Name, device2Changed);
espalexa.addDevice(Device_3_Name, device3Changed);
espalexa.addDevice(Device_4_Name, device4Changed);

// Define your devices functions here.
espalexa.addDevice(Dev_Func_1_Name, devFunc1Changed);
espalexa.addDevice(Dev_Func_2_Name, devFunc2Changed);
espalexa.addDevice(Dev_Func_3_Name, devFunc3Changed);


The loop function should be very simple:

void loop()

The last procedure will be the creation of callback functions, or better, what must be done when Alexa sent a command.The below callback function could be adapted for all 4 IoT devices:

void deviceNChanged(uint8_t brightness)
  //Control the device 
  if (brightness == 255)
      digitalWrite(RelayPinN, HIGH);
      Serial.println("DeviceN ON");
    digitalWrite(RelayPinN, LOW);
    Serial.println("DeviceN OFF");

Changing “N” on above code by 1, 2 3 and 4, you will have the 4 direct callback functions. Remember that brightness parameter sent by Alexa, contains the new device state that will be: 0 ==> OFF; 255 ==> ON, and 1-254 for “dimmed light”.

So, we can expand the above simple ON-OFF function for a special function where a light intensity can be controlled. We will do this for device1 (the Red LED):

void device1Changed(uint8_t brightness){
//Control the device
if (brightness == 255)
  digitalWrite(RelayPin1, HIGH);
  Serial.println("Device1 ON");
else if (brightness == 0)
  digitalWrite(RelayPin1, LOW);
  Serial.println("Device1 OFF");
  int brigh_perc = (brightness/255.)*100;
  analogWrite(RelayPin1, brightness);
  Serial.print("Device1 Brightness: ");

Remember that the NodeMCU has PWM outputs that can be used with Arduino analogWrite() function. If an ESP32 is used, the PWM function should be created once the analogWrite() is not available.

The complete code can be downloaded from my GitHub: Alexa_NodeMCU_Home_Automation

Do not forget to change the dummy wifi credentials, with your own.

Once you compile the code on Arduino IDE and upload it to the NodeMCU, on the Serial monitor you can see the messages exchanged. Once the NodeMCU is connected to your wifi, a similar message (you your network data), should appear:


We are taking in consideration that you already have an Alexa properly installed on the same network where your NodeMcu is connected.Now, let’s ask to Alexa to find your devices. There are 2 methods to do it:

  • Using the Alexa App in your Smartphone
  • Asking Alexa to do it directly using voice command, like: “Alexa,discovery devices“.

After 45 seconds, you should receive Alexa confirmation that 7 devices were found. You can see than on the App “Light tab” as below:


Once Alexa has discovery your devices, you can give her voice commands as shown below:

The below screenshot shows the Serial monitor response.


7. Assembling the Complete HW

Instead of LEDs and resistors, the Outputs GPIOs of should be connected to 4-Channel Relay model as below:


Do not power the Relay-Module directly from the NodeMcu 5V output pin. Use instead an external Power supply for that. A 1A Power Supply should be enough. Confirm with the Relay-Module manufacturer if another version is used. Do not forget to connect the GNDs all together.

In principle, the same code developed for testing can be used, BUT you must confirm the logic used by the Relay-Module. In the above module, for example, you should keep the inputs “Open” or HIGH, changing to LOW to activate the Relay output. So, the code must be changed accordantly.

  • During setup() phase, define GPIOs outputs as HIGH
  • On CallBack functions change HIGH for LOW and vice-versa

You can confirm that relays are working properly by both, the sound of output relay closing and fr a red led in the module.

Once everything is correctly working is the time for complete installation of our “smart devices”, that are 2 fixed “Lamps” and 2 “general Outlets”, let’s rename them properly:

  • Light One
  • Light Two
  • Outlet One
  • Outlet Two
// device names
String Device_1_Name = "Light One"; 
String Device_2_Name = "Light Two";
String Device_3_Name = "Outlet One";
String Device_4_Name = "Outlet Two";

To complete our project as shown on the video at start of this tutorial, connect some devices to be controlled by relays. In my case I use two LEDs as lamps and connect a fan on outlet 1 and a buzzer on outlet 2 (to simulate a device as a radio for example). Below diagram show the appliances installed.

Final diagram.png

Note that once the relays are real, you can install real Lamps and appliances to be controlled using Alexa.


As always, I hope this project can help others find their way in the exciting world of electronics and IoT!

Please visit my GitHub for updated files: Alexa_NodeMCU_Home_Automation

Saludos from the south of the world!

See you at my next tutorial!

Thank you


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