555

Could you clarify what you mean by "555"? It can refer to a few different things. Here are the most common possibilities:

1. 555 timer IC (electronics)

• Pinout (8 pins): 1 GND, 2 Trigger, 3 Output, 4 Reset, 5 Control, 6 Threshold, 7 Discharge, 8 Vcc
• Modes: Astable (oscillator), Monostable (one-shot), Bistable (flip-flop)
• Key formulas (approximate):
  • Astable: f ≈ 1.44 / ((R1 + 2R2) C) T_high ≈ 0.693 (R1 + R2) C T_low ≈ 0.693 R2 C
  • Monostable: T ≈ 1.1 R C
• Quick example: If R1 = 1 kΩ, R2 = 10 kΩ, C = 100 nF, f ≈ 1.44 / ((1k + 20k) × 100 nF) ≈ 680 Hz

2. The number 555 (math)

• Decimal value: 555
• Prime factorization: 3 × 5 × 37
• Divisibility: divisible by 3 and 5 (and by 15, since 555 ÷ 15 = 37)
• Roman numeral: DLV
• Binary: 1000101011
• Hexadecimal: 0x22B

If you tell me which interpretation you want (or the exam topic), I can tailor a quick study sheet or walk you through practice problems.