555

Not sure what you want about 555. Here are a few common exam contexts. Tell me which one (or something else) you mean and your level, and I’ll tailor it.

• Math (number 555)

  • 555 = 3 × 5 × 37 (odd composite)
  • Divisible by 3 and 5; also by 15; 555 ÷ 15 = 37
  • Roman numeral: DLV
  • Binary: 1000101011₂
  • Octal: 1053₈
  • Hex: 0x22B

• Electronics (555 timer IC)

  • A versatile timer used in monostable and astable modes
  • Key formulas (approx):
    • Astable frequency: f ≈ 1.44 / ((R1 + 2R2) C)
    • Duty cycle: D ≈ (R1 + R2) / (R1 + 2R2)
    • Monostable pulse width: t ≈ 1.1 × R × C
  • Pins: Trigger, Threshold, Discharge, Output, Control voltage, Vcc, GND

• Thai/online slang

  • 555 = laughter (5 pronounced “ha” in Thai)

If you pick one, I’ll give you a concise explanation, key formulas, and a couple of practice problems.