Third Eye Kit, Node A: Upper Ranging (Glasses)
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MICROCONTROLLER: Arduino Mini Pro (3.3V or 5V)

SENSOR WIRING (HC-SR04 Ultrasonic):
────────────────────────────────────
  Sensor Pin | Arduino Pin | Function
  ─────────────────────────────────────
  VCC        | +5V         | Power (5V)
  GND        | GND         | Ground
  TRIG       | D9          | Trigger pulse
  ECHO       | D10         | Echo measurement

AUDIO OUTPUT (3.5mm Headphone Jack):
──────────────────────────────────────
  Jack Pin   | Arduino Pin | Function
  ─────────────────────────────────────
  Left       | D11         | Audio signal (PWM)
  Right      | D11         | Audio signal (PWM)
  Ground     | GND         | Ground

OPTIONAL HAPTIC (Vibration Motor):
───────────────────────────────────
  Motor Pin  | Arduino Pin | Function
  ─────────────────────────────────────
  Positive   | D6          | Control signal
  Negative   | GND         | Ground

POWER:
──────
  Lithium cell (1.5V) or AA battery
  Connected to Arduino RAW pin or USB power during development

FIRMWARE CONFIGURATION (node_a.ino):
────────────────────────────────────
  #define TRIG_PIN  9      // Trigger pin
  #define ECHO_PIN  10     // Echo pin
  #define AUDIO_PIN 11     // Audio feedback (PWM)
  #define ALERT_CM  70     // Alert distance in cm (TUNE THIS PER USER)

TUNING NOTES:
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- ALERT_CM typically ranges 50 to 90 cm depending on user height and walking speed
- Start at 70 cm and adjust based on field testing
- Document final value in build log

TESTING:
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1. Upload firmware to Arduino Mini
2. Open Serial Monitor (9600 baud)
3. Slowly move obstacle (hand, book) across sensor cone
4. Verify audio tone plays when distance < ALERT_CM
5. Adjust ALERT_CM until feedback distance feels natural for user

TROUBLESHOOTING:
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- No audio output: Check headphone jack connection, verify D11 is PWM-capable
- Distance always 0: Check HC-SR04 power and pin connections
- Erratic readings: Sensor may be damaged; try spare HC-SR04