555

Could you clarify what you mean by "555"? It could refer to different exam topics. Here are quick notes for the two most common:

• Math (the number 555)

  • Factorization: 555 = 3 × 5 × 37
  • Divisibility: divisible by 3 and by 5; not by 9
  • Base representations:
    • Binary: 555 = 1000101011₂
    • Hexadecimal: 555 = 0x22B
  • Other small facts: sum of digits = 15; digital root = 6

• Electronics (555 timer IC)

  • Modes:
    • Astable: produces a continuous square wave
      • f ≈ 1.44 / ((RA + 2 RB) C)
      • Th ≈ 0.693 (RA + RB) C, Tl ≈ 0.693 RB C
      • Duty cycle ≈ (RA + RB) / (RA + 2 RB)
    • Monostable: one-shot pulse when triggered
      • t ≈ 1.1 RC
  • Pins: VCC, GND, OUT, TRIG, THR, DIS, CTRL (pin 5)
  • Tips: use decoupling capacitor on CTRL pin; tolerances in R, C affect timing

If you tell me which subject and what you need (a quick summary, formulas, worked examples, practice problems), I can tailor a practice sheet or walk you through a problem step-by-step.