CHAPTER 3 ■ COMMUNICATION PROTOCOLS
The sensor will act as a publisher and publish a new message to the codifythings/
intrusionDetected topic on the MQTT broker as soon as an intrusion is detected. The
MQTT broker will add this message to the topic. The mobile app will be a subscriber of
the codifythings/intrusionDetected topic. Whenever a new message is published to the
topic, it will get notified. This will result in the mobile app creating a notification for the app
user. You will build this system in Chapter 6.
Remote Lighting Control
Another great usage of MQTT is developing mobile apps that act as remote controls for
various types of devices, such as a lighting control app. As shown in Figure 3-6 , a remote
control app will also consist of three components, but compared to the previous example
the order of first two components is reversed. That means the first component is a
mobile app that lets the user switch the lights on or off, the second component is a device
connected to lights, and the third component is a topic on an MQTT broker.
Figure 3-6. Components of the remote lighting control
Mobile app users interact with the app to turn the lights on or off, whatever selection
is made the mobile app will publish a new message to the codifythings/lightsControl
topic on the MQTT broker. The MQTT broker will add this message to the topic. The
device that is connected to the physical lights will be a subscriber of the codifythings/
lightsControl topic. Whenever a new message is published to the topic it will get
notified; the device as a result will turn the lights on or off. You will build this remote
control in Chapter 8.
■ Note For hardware and software requirements and circuit instructions, refer to the
“Arduino Uno Wireless Connectivity (WiFi)” section in Chapter 2.