555

Do you want notes on 555 for math, electronics (555 timer), or something else? Here are quick cheats for the two most common contexts.

Math (number 555)

• Factorization: 555 = 3 × 5 × 37
• Digits sum: 5+5+5 = 15, so 555 is divisible by 3 and by 5.
• Basic representations:
  • Decimal: 555
  • Roman numerals: DLV
  • Binary: 1000101011 (since 2^9 + 2^5 + 2^3 + 2^1 + 2^0 = 512 + 32 + 8 + 2 + 1 = 555)
• Other quick facts:
  • 555 is not prime; it’s a product of small primes.
  • 555 is 15 × 37, with 15 and 37 coprime.

Electronics (555 timer IC)

• Pinout (385 miniplan): 1 GND, 2 Trigger, 3 Output, 4 Reset, 5 Control, 6 Threshold, 7 Discharge, 8 Vcc.
• Astable mode (free-running):
  • t_high = 0.693 × (R_A + R_B) × C
  • t_low = 0.693 × R_B × C
  • Frequency: f ≈ 1.44 / [(R_A + 2R_B) × C]
• Monostable mode (one-shot):
  • Triggered by a negative pulse on pin 2.
  • Output stays high for t = 1.1 × R × C (using the timing resistor R and capacitor C).
• Key notes:
  • Control pin (pin 5) can be used to modulate the threshold with a capacitor or external reference.
  • Typical components: choose C for desired timing, then pick R to set f or t.
• Common uses: timers, pulse-width modulation (PWM) with astable configurations, simple delay circuits.

If you tell me which context you’re studying (math, electronics, or something else), I can tailor more detailed examples or practice problems.