Arduino Bicycle Speedometer — Kyoto Award 2019

One-liner. LCD speed & trip distance (0–45 km/h), analog servo needle, Hall pulses, and LDR/CDS-based night LEDs for safer cycling. Awarded Excellence in Electronics (Kyoto, 2019).

Demo ↓ (GIF / MP4)

▶ Full demo video (MP4)

---

Features

• Live speed (km/h) and trip distance (km) on a 16×2 I²C LCD.
• Analog needle: servo angle linearly maps to speed (0–45 km/h).
• Night mode: when ambient light drops below a threshold (LDR/CDS), front and rear LEDs turn on automatically.
• Simple build: reproducible wiring; wheel circumference is fully configurable.

---

Hardware (BOM)

• MCU: Arduino Uno or Nano (Nano recommended for compact installs).
• Speed sensing: Hall-effect sensor (e.g., A3144) + neodymium spoke magnet.
• Display: 16×2 LCD with I²C backpack (PCF8574).
• Servo: SG90 (9 g).
• Lighting: 2× LEDs (white = front, red = rear) + 220–330 Ω series resistors.
• Ambient light: LDR/CDS + 10 kΩ resistor (voltage divider).
• Power: regulated 5 V (buck from Li-ion 18650 / power bank) or 4×AA via a 5 V regulator.
• Misc: hookup wire, heat-shrink, zip ties, 3M pads/brackets for the sensor and magnet.

Optional: driver transistors or a dedicated LED module for brighter headlights; EEPROM buttons for on-bike wheel calibration.

---

Wiring / Schematic

Fritzing files

• PNG: hardware/fritzing/diagram.png
• Source: hardware/fritzing/diagram.fzz

Default pinout (Arduino Uno/Nano):

Module	Arduino Pin	Notes
Hall sensor (A3144)	D2 (INT0)	Interrupt on edge; use INPUT_PULLUP.
Servo SG90	D9 (PWM)	Power from 5 V; share common GND.
LCD 16×2 (I²C)	SDA=A4, SCL=A5	Typical I²C address 0x27 or 0x3F.
LDR (divider)	A0	Second leg: 10 kΩ to GND.
Front LED	D3 (PWM)	220–330 Ω in series with the anode.
Rear LED	D5 (PWM)	220–330 Ω in series with the anode.

Pins are configurable in the sketch’s config block.

---

How it works (math)

• Wheel circumference: C = π · D (meters).
  Example: 700×25C → 2.096 m (≈ 2096 mm).
• Hall pulses: 1 magnet = 1 pulse = 1 revolution (or set PULSES_PER_REV if different).
• Speed:
  speed_kmh = (pulses_per_second / PULSES_PER_REV) * C_m * 3.6
• Trip distance:
  trip_km += (pulses * C_m) / 1000

---

Firmware

Dependencies

• Arduino IDE 1.8+ or 2.x
• Libraries:
  • LiquidCrystal_I2C (any compatible fork)
  • Servo (built-in)
  • (optional) EEPROM for persisting calibration

Certificate — Kyoto 2019

Award: Excellence in Electronics, KIT Summer School (Kyoto, 2019)

_{Click the image for the full-resolution PDF}