Overview of Physical Works in IoT

This blog will provide an overview of the physical layer of IoT devices and how microcontrollers interact with hardware components via GPIO.

Table of contents

What is GPIO?

• GPIO stands for General Purpose Input/Output.
• Standard hardware pins on microcontrollers used to interface with external hardware or communication protocols.
• Provides connections for Power (3.3V / 5V), Ground (0V), and Programmable Pins (Analog / Digital).
• Typically dedicated to one device per set of pins unless using a shared bus protocol (e.g., I2C, SPI).

GPIO Digital Pins

Digital Input (Reading Signals)

Microcontrollers read external voltages relative to Ground to determine binary states:

• HIGH (Bit 1): External voltage is ~3.3V (or 5V, above Ground) → Microcontroller interprets as 1 (HIGH).
• LOW (Bit 0): External voltage is ~0V (equal to Ground) → Microcontroller interprets as 0 (LOW).

Digital Output (Controlling Components)

The microcontroller actively drives voltage at the pin based on your code to control connected components (e.g., turning on an LED, triggering a relay, or sounding a buzzer):

• HIGH (Bit 1): Connects the pin to the internal power rail → Outputs 3.3V (or 5V).
• LOW (Bit 0): Connects the pin directly to Ground → Returns to 0V.

GPIO Analog Pins

• Analog pins can send or receive a range of voltages from 0 to 3.3/5V.
• Input pins use an ADC to convert to a 10-bit number.
• Output pins use an DAC to convert from a 10-bit number.

Hardware Communication Protocols

Microcontrollers use serial protocols to communicate with sensors, displays, and peripheral chips. Here are the 3 main protocols in IoT:

1. I²C (Inter-Integrated Circuit)

• What it is: A 2-wire synchronous bus protocol for connecting multiple low-speed sensors over shared lines.
• Signal Wires (2):
  • SDA (Serial Data): Carries bidirectional data packets.
  • SCL (Serial Clock): Clock signal driven by the controller.
• Key Advantage: Uses unique 7-bit addresses so up to 127 devices can share just 2 signal pins.

2. UART (Universal Asynchronous Receiver-Transmitter)

• What it is: A 2-wire asynchronous protocol used for direct 1-to-1 communication between two devices.
• Signal Wires (2):
  • TX (Transmit): Sends data → connects to RX on the receiving device.
  • RX (Receive): Receives data → connects to TX on the transmitting device.
• Key Advantage: No clock line required; both devices simply agree on a fixed baud rate (speed).

3. SPI (Serial Peripheral Interface)

• What it is: A synchronous protocol designed for ultra-high-speed data transfers across multiple peripherals using dedicated Chip Select lines.
• Signal Wires (4+):
  • COPI (Controller Out Peripheral In): Controller sends data to peripheral (formerly MOSI).
  • CIPO (Controller In Peripheral Out): Peripheral sends data to controller (formerly MISO).
  • SCLK (Serial Clock): Clock signal driven by the controller to synchronize data transfer.
  • CS / CS1, CS2… (Chip Select): Dedicated enable lines used by the controller to select and talk to specific target peripherals on the bus.
• Key Advantage: Extremely fast full-duplex communication (ideal for LCD screens, SD cards, and high-speed flash memory).

4. Wireless Protocols

• IoT devices can also communicate over wireless.
• BLE, WiFi, LoRa, Zigbee and 5G are common wireless protocols used in IoT.

⚡ Quick Protocol Comparison

📖 Series Navigation

👈 Back to Part 4: Connect your device to the Internet
👉 Continue to Part 6: Getting Started with PlatformIO

📚 Complete IoT Getting Started Series

1. Part 1: Introduction to Internet of Things (IoT)
2. Part 2: Deeper Dive into Internet of Things (IoT)
3. Part 3: Sensors and Actuators in Internet of Things (IoT)
4. Part 4: Connect your device to the Internet
5. Part 5: Overview of Physical Works in IoT
6. Part 6: Getting Started with PlatformIO