555

Do you mean something about the number 555, the 555 timer IC, or something else? Here are quick notes for a few common contexts. Tell me which you want to study.

• Math (555 as a number)

  • Prime factorization: 555 = 3 × 5 × 37
  • Divisible by: 3 and 5 (digit sum = 15)
  • Number of divisors: (1+1)(1+1)(1+1) = 8
  • Roman numeral: DLV
  • Binary: 1000101011
  • Hex: 0x22B

• Electronics (555 timer IC)

  • Modes: astable and monostable
  • Pinout (8-pin): GND, Vcc, Trigger, Output, Reset, Discharge, Threshold, Control
  • Astable frequency: f ≈ 1.44 / [(R1 + 2R2) C]
  • Astable high/low times: tH = 0.693 (R1 + R2) C, tL = 0.693 R2 C
  • Monostable pulse width: t = 1.1 R C
  • Common uses: oscillators, timers, PWM-like pulses

• Other contexts

  • 555 as a fictitious phone prefix in media
  • In other bases or representations (e.g., base-10 to base-n conversions)

Which one would you like to dive into? If you have a specific exam problem, paste it and I’ll help you solve it.