Meet the Devices

Let’s look at what’s actually in that room. We have a device with a temperature sensor. Maybe it also has a fan. Let’s break down what each part does.

Sensor: Reading the World

A sensor reads something from the physical world. In our story, it’s a temperature sensor.

What it does:

• Measures temperature
• Outputs a number (like 23.4°C)
• Does this automatically, on a schedule

Other examples:

• Motion sensor: detects movement (true/false)
• Light sensor: measures brightness (a number)
• Humidity sensor: measures moisture (a percentage)

Key point: Sensors only read. They don’t change anything.

Actuator: Changing the World

An actuator changes something in the physical world. In our story, we might have a fan.

What it does:

• Turns the fan on or off
• Can control speed (low, medium, high)
• Responds to commands from the device

Other examples:

• Light: turns on/off, dims
• Relay: switches power to other devices
• Motor: moves something

Key point: Actuators only act. They don’t read anything.

Device/Node: The Small Computer

The device (also called a “node”) is the small computer that owns the sensor and actuator.

What it does:

• Reads from sensors
• Controls actuators
• Runs code (your program)
• Connects to the network
• Sends data to the cloud

What’s inside:

• CPU (processor)
• Memory (RAM)
• Storage (flash memory)
• Network interface (Wi-Fi chip, Ethernet port, etc.)
• GPIO pins (connect sensors and actuators)

In our story:

• One temperature sensor connected
• One fan connected (optional)
• Wi-Fi for network connection
• Code that reads sensor every 10 seconds

Gateway: The Bridge (Optional)

A gateway bridges your local network to the internet. Not all systems need one.

When you need it:

• Devices use a different protocol (like Zigbee or Bluetooth)
• Devices can’t connect directly to Wi-Fi
• You want to manage many devices locally first

What it does:

• Receives data from local devices
• Translates between protocols
• Sends data to the cloud
• Can buffer data if cloud is offline

In our story:

• We don’t need a gateway
• Device connects directly to Wi-Fi
• Goes straight to the cloud

Our Device Setup

For this tutorial, we have:

Device (MCU - Microcontroller Unit)

• Small computer board
• Runs our code
• Has Wi-Fi

Temperature Sensor

• Connected to the device
• Reads temperature every 10 seconds
• Sends value to device

Fan (Optional)

• Connected to the device
• Can be turned on/off
• Controlled by device code

Network Connection

• Wi-Fi connection
• Device talks directly to cloud
• No gateway needed

Visual Breakdown

Here’s how the components connect:

Quick Check

Which part talks to the cloud?

• The device. It reads from the sensor, creates a message, and sends it over Wi-Fi.

Which part touches the physical world?

• The sensor (reads temperature) and the actuator (controls fan). The device itself is just a computer.

What’s the difference between sensor and actuator?

• Sensor reads (input). Actuator acts (output). One measures, the other changes.

Real-World Examples

Smart Thermostat

• Sensor: temperature
• Actuator: HVAC system control
• Device: the thermostat itself

Smart Light

• Sensor: motion (optional)
• Actuator: the light bulb
• Device: smart switch or bulb

Security Camera

• Sensor: camera (captures images)
• Actuator: none (or LED indicator)
• Device: the camera unit

What’s Next?

Now that you know what the device is, let’s see what happens when it reads the sensor. In the next page, we’ll turn that raw temperature reading into a message that can travel to the cloud.