555

Do you mean the 555 timer IC or the number 555? I can give you a quick cheat sheet for electronics, or math facts for the number. Here are both so you can pick:

If you mean the 555 timer IC (common in exams):

• What it is: An 8-pin timer used in monostable, astable (oscillator), and bistable configurations.
• Pinout (8-pin DIP):
  • Pin 1 = GND
  • Pin 2 = Trigger
  • Pin 3 = Output
  • Pin 4 = Reset
  • Pin 5 = Control Voltage (often with a 10 nF cap to ground)
  • Pin 6 = Threshold
  • Pin 7 = Discharge
  • Pin 8 = Vcc
• Modes and basics:
  • Monostable: One-shot pulse when triggered. Pulse width t = 1.1 R C.
  • Astable: Free-running oscillator. Frequency f ≈ 1.44 / ((R1 + 2R2) C). On-time t_on ≈ 0.693 (R1 + R2) C; Off-time t_off ≈ 0.693 R2 C.
  • Bistable: Latch/flip-flop operation (set/reset via inputs).
• Quick formulas you’ll reuse:
  • Astable: f = 1.44 / ((R1 + 2R2) C)
  • Astable pulses: t_on = 0.693 (R1 + R2) C, t_off = 0.693 R2 C
  • Monostable: t = 1.1 R C
• Tips:
  • Diode across R2 in astable can give a wider duty cycle range.
  • Use a small capacitor on control voltage (Pin 5) for stability.
  • Vcc range and component choice depend on the version (NE555, LMC555, etc.).
• Common variants: NE555, LM555, CMOS 7555 (lower current, higher impedance).

If you mean the number 555 (math facts):

• Decimal value: 555
• Prime factorization: 3 × 5 × 37
• Binary: 1000101011
• Hexadecimal: 0x22B
• Roman numeral: DLV
• Other quick notes: 555 is divisible by 5, ends with 5 so it's a multiple of 5.

Which would you like to dive into (practice problems, example circuits, or more math problems)?