555

Do you mean the 555 timer IC? If yes, here’s a quick refresher and a couple of practice problems.

Key configurations

• Astable (free-running oscillator): no external trigger. Output toggles high/low continuously.
  • t_high = 0.693 (R_A + R_B) C
  • t_low = 0.693 R_B C
  • f ≈ 1.44 / ((R_A + 2R_B) C)
  • Duty cycle = t_high / (t_high + t_low)
• Monostable (one-shot): output goes high for a period after a trigger.
  • t = 1.1 R C (R is the timing resistor, C is the timing capacitor)
• Bistable (flip-flop): output latches; triggered by pins 2/6 and reset pin.

Example problems

1. Astable example

• R_A = 1 kΩ, R_B = 2 kΩ, C = 100 nF
• t_high = 0.693 × (1k + 2k) × 100 nF = 0.693 × 3,000 × 100e-9 ≈ 0.000208 s
• t_low = 0.693 × 2k × 100 nF = 0.693 × 2,000 × 100e-9 ≈ 0.000139 s
• Period ≈ 0.000346 s → f ≈ 1 / 0.000346 ≈ 2.88 kHz
• Duty cycle ≈ 0.208 / 0.346 ≈ 60%

2. Monostable example

• R = 10 kΩ, C = 100 nF
• t ≈ 1.1 × 10,000 × 100e-9 = 1.1 ms

If you’re studying for a specific course or have a problem from a homework/test, tell me the exact circuit values and I’ll solve it step-by-step. Want quick practice questions or a printable cheatsheet of formulas?