Communication is the process of transferring information from one entity to another in a reliable and controlled manner.

In embedded systems, communication allows:

• Microcontrollers to talk to sensors
• Processors to talk to memory
• Devices to talk to other devices
• Systems to talk to cloud platforms
• Humans to talk to machines

Without communication, a microcontroller is just a calculator with no awareness of the outside world.

At the lowest level, communication is always:

Information → Encoding → Transmission → Decoding → Action

Now let’s formalize this using the basic communication model.

The Basic Communication Model

Every communication system contains three fundamental elements:

+----------+        Medium         +----------+
| Sender   | --------------------> | Receiver |
+----------+                       +----------+
        ^                                |
        |                                |
        +------------ Feedback -----------+

Components Explained

• Sender (Transmitter)

Generates the data.

• Medium (Channel)

Carries the signal (wire, air, fiber, etc.).

• Receiver

Interprets the signal and extracts information.

• Noise

Unwanted disturbance that corrupts data.

         Noise
           ↓
Sender → Channel → Receiver

In embedded systems, noise is a serious enemy:

• Electro Magnetic Interference (EMI)
• Crosstalk
• Voltage spikes
• Radio Frequency Interference (RFI)

Understanding this model leads us to the next important question:

How is the data physically represented?

Signals: Analog vs Digital

Before discussing wired or wireless, we must understand signal types.

Analog Signals

Continuous waveform.

Voltage
  |
  |     /¯\      /¯\       /¯\
  |    /   \    /   \     /   \
  |___/     \__/     \___/     \____ Time

Used in:

• Audio
• Radio
• Sensors (temperature, pressure)

Digital Signals

Discrete logic levels.

Voltage
  |
5V| ┌───────┐      ┌───────┐
  | │       │      │       │
0V└─┘       └──────┘       └──── Time

Used in:

• Microcontrollers
• Digital buses
• Computers

Digital communication dominates embedded systems because it is:

• Noise resistant
• Easy to process
• Reliable over distance (with proper design)

Now that we understand signals, we can divide communication into its two major physical categories.

Wired Communication

Wired communication uses a physical conductor to transmit signals.

MCU_A  ======= Copper/Fiber =======  MCU_B

The medium may be:

• Copper wire
• Twisted pair
• Coaxial cable
• Optical fiber

Advantages

• High reliability
• High speed
• Low latency
• Secure (harder to intercept physically)

Disadvantages

• Physical installation required
• Limited mobility
• Cable management complexity

Now let’s break wired communication further.

Wired Communication Types in Embedded Systems

Parallel Communication

Multiple data lines transmit bits simultaneously.

D0 ───────────────
D1 ───────────────
D2 ───────────────
D3 ───────────────
CLK───────────────

Used in:

• Old microprocessor buses
• External memory interfaces

Pros

• High speed

Cons

• Many pins
• Crosstalk
• PCB routing complexity

Because of these limitations, industry shifted toward serial communication.

Serial Communication

Bits are transmitted one after another on fewer wires.

Data: 1 0 1 1 0 0 1
Line: ──▁▔▔▁▁▔────

This reduces:

• Pin count
• PCB complexity
• EMI

Now let’s see real-world serial protocols.

UART (Universal Asynchronous Receiver Transmitter)

Point-to-point communication.

MCU_A TX ───────── RX MCU_B
MCU_A RX ───────── TX MCU_B
GND     ───────── GND

Characteristics:

• Asynchronous
• No clock line
• Uses baud rate agreement

Used in:

• Debug consoles
• GPS modules
• Bluetooth modules

SPI (Serial Peripheral Interface)

High-speed synchronous communication.

        Master
         |
   MOSI ──────────┐
   MISO ──────────┤
   SCLK ──────────┤
   CS   ──────┐   │
               │   │
            +-------+
            | Slave |
            +-------+

Characteristics:

• Full duplex
• High speed
• Short distance

Used in:

• Displays
• ADC/DAC
• Flash memory

I2C (Inter-Integrated Circuit)

Multi-device two-wire bus.

SDA ─────────┬────────┬────────
SCL ─────────┬────────┬────────
             |        |
           Slave1   Slave2

Characteristics:

• Address-based
• Multi-master possible
• Lower speed than SPI

Used in:

• Sensors
• EEPROM
• RTC

CAN (Controller Area Network)

Designed for automotive robustness.

MCU1 ----\
MCU2 ----- CAN_H / CAN_L ----- MCU3
MCU4 ----/

Features:

• Differential signaling
• Error detection
• Arbitration

Used in:

• Automotive ECUs
• Industrial systems

Now that we understand wired communication, let's transition naturally to wireless communication — where the medium is no longer copper, but air.

Wireless Communication

Wireless communication transmits data using electromagnetic waves.

Device A  )))))    AIR    (((((  Device B

Instead of voltage levels on wires, we transmit:

• Radio waves
• Infrared waves
• Microwave signals

Advantages

• Mobility
• No cabling
• Easy deployment

Disadvantages

• Interference
• Security risks
• Higher power consumption
• Regulatory constraints

Wireless communication requires modulation — encoding data into a radio carrier.

Data → Modulation → RF Signal → Antenna → Air

Now let's explore the common wireless technologies used in embedded systems.

Common Wireless Technologies in Embedded Systems

Wi-Fi

High data rate networking.

ESP32 )))))  Router  ((((( Cloud

Features:

• TCP/IP stack
• High bandwidth
• Higher power consumption

Used in:

• IoT devices
• Smart home systems

Bluetooth & BLE

Short-range communication.

Phone ))))   BLE   (((( Sensor

BLE is:

• Low energy
• Ideal for battery devices

Used in:

• Wearables
• Beacons
• Health monitors

Zigbee

Mesh-based low power communication.

Node1 )) Node2 )) Node3 )) Node4

Features:

• Mesh topology
• Low data rate
• Long battery life

Used in:

• Smart lighting
• Building automation

LoRa

Long-range low-power communication.

Sensor ))))))))  Gateway  ((((((( Cloud

Features:

• Kilometer range
• Very low data rate
• Extremely low power

Used in:

• Agriculture
• Smart metering
• Industrial IoT

Wired vs Wireless Comparison

Let’s summarize from a system design perspective.

Engineering Perspective: How to Choose

As a system architect, ask:

• Is mobility required?
• What is the power budget?
• What is the data rate?
• What is the environment (industrial? automotive? home?)?
• What is the security level required?

There is no “best protocol.”

There is only correct protocol for the system constraints.

Network Topology

_(How devices are connected logically)_

Topology defines who communicates with whom.

Star Topology

Used in:

• Bluetooth Low Energy
• Wi-Fi

Structure:

           Device A  
              |  
Device B --- Gateway --- Device C  
              |  
           Device D

All communication goes through a central node.

In BLE:

• Central = phone
• Peripheral = sensors

In Wi-Fi:

• Access Point = center
• Stations = clients

Advantages:

• Simple design
• Easy security control
• Low memory requirement
• Easy debugging

Disadvantages:

• Single point of failure
• Limited coverage
• Central node overload risk

Mesh Topology

Used in:

• Zigbee
• Thread

Structure:

A ---- B ---- C  
 \     |      |  
  \    |      |  
   ----D ---- E

Devices relay messages for others.

If A wants to talk to E:

A → D → E

Advantages:

• Large coverage
• Self-healing
• No single point of failure

Disadvantages:

• Complex routing
• More RAM/Flash required
• Higher power consumption (routers must stay awake)

Star vs Mesh — Embedded Engineering View

If you're building:

• Battery sensor → Star is safer
• Smart building → Mesh scales better