Overview of Digital SignalsBinary RepresentationHexadecimal NotationBit WidthSigned NumbersFloating Point NumbersBringing it TogetherPhysical Communication LayersKnowledge Check

Physical Communication Layers

⚡ RS-232 (Voltage Based)

  • Speed: Up to 115.2 kbps
  • Distance: Up to 15m
  • Signal: ±3V to ±15V
  • Wiring: 3-wire minimum (TX, RX, GND)
  • Pros: Simple, widely supported, point-to-point
  • Cons: Limited distance, susceptible to noise
  • Use case: Direct device connections, legacy equipment

🔄 RS-485 (Voltage Based)

  • Speed: Up to 10 Mbps
  • Distance: Up to 1200m
  • Signal: Differential ±5V
  • Wiring: 2-wire (A+, B-) or 4-wire
  • Pros: Long distance, noise immune, multi-drop
  • Cons: Requires termination, addressing
  • Use case: Industrial networks, Modbus RTU

🚗 CAN Bus (Current Based)

  • Speed: Up to 1 Mbps (30m) or 500 kbps (100m)
  • Distance: 30m-1000m (speed dependent)
  • Signal: Differential ±2V
  • Wiring: 2-wire (CAN-H, CAN-L)
  • Pros: Highly reliable, priority-based
  • Cons: Complex protocol, limited message size, requires termination, distance drops quickly with speed
  • Use case: Automotive, industrial control

🦷 Bluetooth

  • Speed: Up to 2 Mbps (BLE 5)
  • Distance: Up to 100m (Class 1)
  • Signal: 2.4GHz RF
  • Wiring: Wireless
  • Pros: Low power, widespread support
  • Cons: Limited range, interference prone
  • Use case: Personal devices, IoT peripherals

📶 Wi-Fi

  • Speed: Up to 9.6 Gbps (Wi-Fi 6)
  • Distance: Up to 100m (indoor)
  • Signal: 2.4GHz / 5GHz RF
  • Wiring: Wireless
  • Pros: No wiring, high bandwidth
  • Cons: Security concerns, interference
  • Use case: Office networks, IoT devices

📡 LoRa

  • Speed: 0.3-50 kbps
  • Distance: Up to 10km (urban), 40km (rural)
  • Signal: Sub-GHz RF
  • Wiring: Wireless
  • Pros: Long range, low power
  • Cons: Low bandwidth, latency
  • Use case: IoT sensors, remote monitoring

💡 Fiber Optic

  • Speed: Up to 100+ Gbps
  • Distance: Up to 100km+
  • Signal: Light pulses
  • Wiring: Fiber optic cable
  • Pros: Fastest, immune to EMI
  • Cons: Expensive, fragile
  • Use case: Backbone networks, long distance

⚡ Power Line Communication

  • Speed: Up to 200 Mbps
  • Distance: Up to 1km
  • Signal: High frequency over power lines
  • Wiring: Existing power lines
  • Pros: Uses existing infrastructure
  • Cons: Noise sensitive, variable performance
  • Use case: Smart meters, home automation
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Evolution of Digital Signaling

Single-Ended Voltage Signaling (RS-232)

Transmitter
Logic 1: -12V Logic 0: +12V
Single Wire + Ground Reference
Susceptible to Noise & Ground Shifts
Receiver
Threshold: >-3V = Logic 1 <+3V = Logic 0
  • ❌ Ground reference must be shared
  • ❌ Susceptible to electromagnetic interference
  • ❌ Limited distance due to voltage drop
  • ✓ Simple to implement

Differential Voltage Signaling (RS-485)

Transmitter
Logic 1: A=+2V, B=-2V Logic 0: A=-2V, B=+2V
Balanced Differential Pair
Common Mode Noise Cancellation
Noise affects both lines equally
Receiver
Logic determined by voltage difference: A-B > +200mV = 1 A-B < -200mV = 0
  • ✓ Excellent noise immunity
  • ✓ No shared ground required
  • ✓ Long distance capable
  • ❌ Requires two wires

Current-Based Signaling (CAN)

Transmitter
Dominant (0): CAN-H: Source +3.5V CAN-L: Sink to +1.5V
Recessive (1): Both lines: +2.5V
CAN-H and CAN-L Lines
Dominant State: 2V difference
Recessive State: 0V difference
Receiver
Differential voltage: >0.9V = Dominant (0) <0.5V = Recessive (1)
  • Immune to voltage drops
  • ✓ Excellent noise immunity
  • ✓ Built-in collision detection (dominant wins)
  • ✓ Wired-AND behavior enables arbitration
  • ❌ More complex transceivers

Signal States and Frame Structure:

  • Default Network State: Recessive (1)
    • • Network is naturally pulled to recessive state (2.5V on both lines)
    • • All nodes must actively drive the bus to achieve dominant state
    • • Makes error detection easier - dominant state requires energy
  • Start of Frame (SOF): Always Dominant (0)
    • • Transition from idle (1) to dominant (0) marks frame start
    • • All nodes synchronize on this falling edge
    • • Natural part of protocol - no special encoding needed
  • Signal States:
    • • Recessive (1): Both lines at ~2.5V (differential = 0V)
    • • Dominant (0): CAN-H = 3.5V, CAN-L = 1.5V (differential = 2V)
  • Arbitration: Dominant bits override recessive bits
    • • Multiple nodes can start transmitting at the same SOF
    • • Lower ID (more dominant bits) wins arbitration
    • • Losing nodes automatically become receivers

Wireless Network Topologies: WiFi vs LoRa

WiFi Mesh Network

📡💻📱🖨️📺

LoRa Point-to-Point Network

🔌📡📶🔋InverterLoRa TXLoRa RXMeter

Key Topology Differences:

WiFi (Area Coverage)
  • Forms interconnected mesh network
  • Devices can communicate peer-to-peer
  • Coverage extends through mesh nodes
  • Higher bandwidth enables media streaming
  • Better for dense device clusters
LoRa (Line Coverage)
  • Star topology with central gateway
  • All communication through gateway
  • Long-distance point-to-point links
  • Optimized for small data packets
  • Better for sparse sensor networks

Key Considerations for Physical Layer Selection

Environmental Factors

  • EMI/RFI interference levels
  • Temperature range
  • Moisture/dust exposure
  • Physical protection requirements

Performance Requirements

  • Required bandwidth
  • Maximum acceptable latency
  • Distance requirements
  • Number of nodes/devices