555

Do you mean the 555 timer IC (electronics) or the number 555 in math? If you’re prepping for exams, tell me the topic and I’ll tailor it. In the meantime, here are quick notes for both:

If you mean the 555 timer IC:

• Pinout (DIP): 1 GND, 2 Trigger, 3 Output, 4 Reset, 5 Control, 6 Threshold, 7 Discharge, 8 Vcc
• Monostable mode:
  • Trigger input pulls low; output goes high for t = 1.1 × R × C (seconds if R in ohms and C in farads)
• Astable mode:
  • t_high = 0.693 × (RA + RB) × C
  • t_low = 0.693 × RB × C
  • Frequency f = 1 / (t_high + t_low) = 1 / [0.693 × (RA + 2RB) × C] ≈ 1.44 / [(RA + 2RB) × C]
  • Duty cycle D = t_high / (t_high + t_low) = (RA + RB) / (RA + 2RB)
• Typical supply: 3–15 V (check datasheet)
• Applications: oscillators, timers, PWM, debouncing, etc.

If you mean the number 555 (math):

• Factorization: 555 = 3 × 5 × 37
• Divisible by 3 and 5 (sum of digits = 15)
• Decimal representation is a repdigit (555)
• In Roman numerals: DLV
• Binary: 555 = 1000101011₂

Tell me which one you want, or share the exact exam topic, and I’ll tailor a concise study guide or example problems.