555

Could you clarify what you want about "555"? Here are the two most common exam topics:

• 555 timer IC (electronics)

  • Pinout: 1 GND, 2 Trigger, 3 Output, 4 Reset, 5 Control Voltage, 6 Threshold, 7 Discharge, 8 VCC
  • Modes:
    • Monostable (one-shot): t ≈ 1.1 · R · C
    • Astable (free-running): f ≈ 1.44 / [(R_A + 2R_B) · C], Duty cycle D ≈ (R_A + R_B) / (R_A + 2R_B)
  • Key tips: Reset active low, control voltage pin often tied to 2/3 VCC via a capacitor, can drive TTL/CMOS loads, typical supply 4.5–15 V.
  • Quick example problems you can practice now:
    • If R = 10 kΩ and C = 100 nF in monostable, t ≈ 1.1 × 10k × 100 nF = 1.1 ms.
    • If RA = 1 kΩ, RB = 10 kΩ, C = 100 nF in astable, f ≈ 1.44 / [(1k + 2×10k) × 100 nF] ≈ 685 Hz.

• Mathematics / number 555

  • Prime factorization: 555 = 3 × 5 × 37
  • Decimal/binary/hex/roman:
    • Binary: 555 = 1000101011₂
    • Hex: 0x22B
    • Roman numeral: DLV
  • Simple properties: sum of digits = 15; divisible by 3 and 5, not by 9 or 11
  • Quick base conversions you can practice (e.g., to octal, ternary)
  • A couple of quick problems you can try:
    • Find all divisors of 555.
    • Express 555 in base 8 (octal).

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