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Electronic circuits that use the 555 Timer

555 Timer Circuits

555 Timers are fun and a great way to start learning electronics

555 Timer Calculator


This page is very useful when creating 555 timer circuits. it will allow you to calculate the frequency and duty cycle.

Astable 555 Square Wave Calculator

In an astable circuit, the output continually switches state between high and low without any intervention from the user. The duration of the high and low states are based on what values you choose for R1, R2 and C1.

The formulas used are:
Time High (secs) = 0.693 * (R1 + R2) * C1
Time Low (secs) = 0.693 * R2 * C1
Frequency = 1.44 / ((R1 + R2 + R2) * C1)
Duty Cycle Percentage = (Th / (Th + Tl)) * 100

Resistor (R1) Ohms
Resistor (R2) Ohms
Capacitor (C1) Farads
Enter R1, R2 and C1, then press Calculate


Monostable 555 Timeout Calculator

This calculator is designed to give the timeout value (D) for a Monostable 555 Timer Circuit. When power is applied to a monostable circuit the output is low until the delay time has elapsed, the output then goes high and remains high.

The formula used is:
Time Out Delay (secs) = 1.1 * R1 * C1

To use this calculator simply enter values for R1 and C1, then press Calculate.

Resistor (R1) Ohms
Capacitor (C1) Farads
Enter R1 and C1, then press Calculate


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Common Mistakes
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Using the Output of a 555 Timer