Blinking an LED (555 Timer)
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This Module is part of the grouping: Blinking LED


Blinking an LED is a simple project that illustrates how to use the 555 Timer in it's astable configuration. You could also buy a stand alone blinking LED but then it would not be a project anymore!

Bill Of Materials

Astable mode


In astable mode, the '555 timer ' puts out a continuous stream of rectangular pulses having a specified frequency. Resistor R1 is connected between VCC and the discharge pin (pin 7) and another resistor (R2) is connected between the discharge pin (pin 7), and the trigger (pin 2) and threshold (pin 6) pins that share a common node. Hence the capacitor is charged through R1 and R2, and discharged only through R2, since pin 7 has low impedance to ground during output low intervals of the cycle, therefore discharging the capacitor.

In the astable mode, the frequency of the pulse stream depends on the values of R1, R2 and C:

f = 1/(ln(2) * C * (R1 + 2R2))

The high time from each pulse is given by

high = ln(2) * (R1 + R2) * C

and the low time from each pulse is given by

low = ln(2) * R2 * C

where R1 and R2 are the values of the resistors in ohms and C is the value of the capacitor in farads.


This page is a Module on bildr. Modules are how-to pages on the creation of objects designed to be expanded upon.

NOTE: All information contained within this article is pure opinion. Although this article is intended to help people, it may contain faulty or misleading information. This article is not to be considered professional opinion or advice, and is in no way a replacement for reading all safety/instructional documentation. Always remember to protect yourself when handling/using hazardous materials, as well as test new techniques before using them on projects/work intended to be handed in or used.

bildr and its contributers take NO responsibility for the information contained within.