Blinking an LED (555 Timer)

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

• 555 Timer
• R1 1500 Ohm resistor
• R2 820 Ohm resistor
• R3,R4 180 Ohm current limiting resistors
• Two LEDs
• C 68 µF capacitor
• 0.01 µF capacitor
• Batteries or other DC 4.5 volt power source

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 V_CC 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.

References

• http://en.wikipedia.org/wiki/555_timer_IC
• http://www.horrorseek.com/home/halloween/wolfstone/TechBase/com555_555TimerCalc.html

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