555

Do you mean the number 555 or the 555 timer IC? Here are quick notes for both. Tell me which you want and your syllabus if you’d like more depth.

• As a number (555)

  • Prime factors: 3 × 5 × 37
  • Repdigit and palindrome
  • Roman numerals: DLV

• 555 timer IC (common in exams on electronics)

  • 8-pin DIP: 1 GND, 2 TRIG, 3 OUT, 4 RESET, 5 CONTROL, 6 THR, 7 DISCH, 8 VCC
  • Modes:
    • Monostable (one-shot): t ≈ 1.1 R C
    • Astable (oscillator): f ≈ 1.44 / ((R1 + 2R2) C); Duty cycle D = (R1 + R2) / (R1 + 2R2)
  • Variants: NE555, LM555; typical Vcc 4.5–15 V; outputs can source/sink current
  • Example problem starter: If R = 10 kΩ and C = 100 nF in monostable mode, t ≈ 1.1 × 10k × 100nF = 1.1 ms

Want a worked example, or notes tailored to your course (electrical engineering, number theory, etc.)?