LiFi Prototype

Description

Experimental Li-Fi system using Arduino for optical wireless data transmission.

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Materials

• 2 Arduino boards — one for transmitter, one for receiver
• 2 Breadboards
• Transmitter: Super bright white LEDs
• Receiver: Solar panel
• Wires

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Protocol

• Default state: HIGH
• Threshold: Set dynamically at startup based on ambient lighting
• Setup: Delay at the beginning to ignore setup noise

Encoding schemes:

• Non-Return-to-Zero (NRZ): HIGH = 1, LOW = 0
• Manchester Encoding: HIGH → LOW = 1, LOW → HIGH = 0

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Experiments

1. Arduino-LED-Solar NRZ

• Transmitter: 3 white LEDs
• Receiver: Solar panel
• Protocol: NRZ on-off
  • Sample in the middle (sampling time * 1.5)
• Setup: Threshold 150; box 25cm × 17cm; transmitter and receiver diagonally placed, 20cm apart
• Performance: Smallest reliable sampling time: 4ms; 3ms works with some errors

2. Arduino-LED-Solar Manchester

• Setup: Same as above
• Protocol: Manchester
  • 1: HIGH → LOW (first half of bit)
  • 0: LOW → HIGH (first half of bit)
  • Receiver samples after < sampling time * 1.5
• Threshold: ~0.6 × LDR value when LED is ON
  • More LEDs → larger optimal threshold range
• Performance: Smallest reliable sampling time: 2ms

3. Arduino-LED-Solar 4B/5B

• Setup: Without box

• Protocol: 4B/5B encoding + NRZ

  • 4-bit nibbles mapped to 5-bit codes (see table below)

  4B Data	5B Code
  0000	11110
  0001	01001
  0010	10100
  0011	10101
  0100	01010
  0101	01011
  0110	01110
  0111	01111
  1000	10010
  1001	10011
  1010	10110
  1011	10111
  1100	11010
  1101	11011
  1110	11100
  1111	11101

• Threshold: Use adaptive rate to adjust threshold dynamically while receiving

  • Able to handle background light changes (e.g., turning on/off room light)
  • Max distance depends on room light intensity

• Performance: Smallest reliable sampling time: 2ms

• TODO: Implement NRZI and use control signals

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TODO

• Implement error detection/correction (e.g., parity bits, checksums)
• Explore other signal encoding methods: color, brightness, timing, on-off combinations
• Transmitter improvements:
  • Use laser
  • Different colors and brightness levels
• Receiver improvements:
  • Replace solar panel with phototransistor for higher sensitivity
• Optimize threshold calculation and sampling time for new setups

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References

• https://charliegerard.dev/blog/lifi-sending-data-light/
• https://www.irjet.net/archives/V12/i4/IRJET-V12I4197.pdf
• https://electronicsworkshops.com/2024/02/09/data-transmission-through-li-fi-using-arduino/#google_vignette
• https://www.instructables.com/LiFi-Experiment-Audio-Transmission-Through-Light/
• https://ieeexplore.ieee.org/document/7916619
• https://www.scirp.org/journal/paperinformation?paperid=80019