555

Do you want help with 555 in math, electronics, or something else? Here are quick notes for the two most common:

• Math basics

  • 555 = 3 × 5 × 37
  • Not prime; divisible by 3, 5, and 15
  • Roman numeral: DLV (500 + 50 + 5)

• Electronics (555 timer IC)

  • Configurations: astable (oscillator) and monostable (one-shot)
  • Astable:
    • f ≈ 1.44 / [(RA + 2 RB) C]
    • Th ≈ 0.693 (RA + RB) C
    • Tl ≈ 0.693 RB C
  • Monostable:
    • Pulse width t ≈ 1.1 R C
  • Typical usage: timing pulses, PWM-ish waveforms, etc.

If you tell me your exam subject and level (e.g., “Intro electronics” or “Intro number theory”), I can tailor a quick problem set or go through a worked example.