Simple 555 Oscilator

Exe I When the output at pin 3 is HIGH, the capacitor charges up through the resistor. When the voltage across the capacitor reaches 2/3Vcc, pin 6 causes the output at pin 3 to change state and goes LOW. The capacitor now discharges back through the same resistor until pin 2 reaches 1/3Vcc causing the output to change state once again. The capacitor continually charges and discharges between 2/3Vcc and 1/3Vcc back and forth through the same resistor creating a HIGH and LOW state at the output, pin 3. As the capacitor charges and discharges through the same resistor, the duty cycle of this basic arrangement is very close to 50% or 1:1. The series of square wave output pulses produced have a cycle time (T) equal to approximately 2(0.693)*RC or 2lin(2)*RC. The output waveform frequency (ƒ) is therefore equal to: 0.722/RC. So for example, if we want to generate a 1kHz output square-wave waveform, then R = 3.3kΩ and C = 220nF using preferred component values.

published 3 years ago