555

Could mean a few things. Which one do you want to focus on?

• 555 timer IC (electrical engineering): quick refresher and formulas

  • Modes: astable, monostable, bistable
  • Astable: f = 1.44 / ((R_A + 2R_B) C)
    • High time Th = 0.693 (R_A + R_B) C
    • Low time Tl = 0.693 R_B C
    • Duty cycle D = (R_A + R_B) / (R_A + 2R_B)
  • Monostable: pulse width t = 1.1 R C
  • Key notes: trigger input (low), thresholds at 2/3 Vcc and 1/3 Vcc, output related to discharge transistor
  • Want a worked example or a problem you’re stuck on?

• Math problem involving the number 555

  • Prime factorization: 555 = 3 × 5 × 37
  • Divisibility, modular arithmetic, digit sums, etc.

• Something else (e.g., meme “555” in Thai): explain or summarize

Tell me which topic and what level (intro, intermediate, exam-style problem), and I’ll tailor a clear explanation or walk you through a solved example.