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Circuits / 555 and op-amps

555 astable blinking an LED

C1 charges through R1 + R2 and discharges through R2: f ≈ 1.44 / ((R1 + 2·R2) · C1)

555 astable blinking an LED, simulated on a breadboard

Tap a part to see its voltages and currents. It is a model, not a measurement.

Predict, measure, explain

  1. Predict How many times a second will the LED blink?
  2. Measure Count the blinks. Then change R2 to 4.7 kΩ.
  3. Explain
    Show the answerHide the answer

    About 6.7 times: R1, R2 and the 10 µF capacitor set the time. With 4.7 kΩ the capacitor charges faster and it blinks about 13 times a second.

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