A 555 monostable pulse

Give one press a timed response

IC means Integrated Circuit: many electronic components on one chip. The 555 timer IC can work as a monostable, with one resting state and one timed pulse after a trigger. A trigger starts the pulse. µF is microfarad, one millionth of a farad of capacitance; ms is millisecond, one thousandth of a second.

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EXPERIMENT BENCH

Change the circuit settings, predict the readings, then check a challenge. These are learning models, with the assumptions explained in each lesson.

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How it works

One ideal trigger at time zero, fixed 5 V supply. The elapsed-time slider selects a sample; it is not a live clock. No retriggering, contact bounce or actual 555 limits. This model is not hardware tested.

Pulse duration T = ln(3) × R × C ≈ 1.099RC. R is timing resistance, C timing capacitance; ln is the natural logarithm. The capacitor charges toward 5 V. At 2/3 of supply, the pulse ends; this model then resets capacitor voltage to zero.

Difficulty

Build · Observe
Power on at 10 kΩ, 10 µF and elapsed time 50 ms. Read output 5 V and pulse duration about 109.861 ms.
Need a hint?
10 kΩ; 10 µF; 50 ms → 5 V; 109.861 ms
Explore · Adjust
Keep 10 kΩ and 10 µF; choose elapsed time at least 120 ms. Obtain output 0 V.
Need a hint?
10 kΩ; 10 µF; 120 ms → 0 V
Solve it · Discover the limit
Design a pulse of 950–1050 ms and choose elapsed time 500 ms so output remains 5 V.
Need a hint?
10 kΩ; 91 µF; 500 ms → 999.737 ms; 5 V

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