IC 555 Monostable Circuit

An introduction to IC 555 timer circuits.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Parts

IC 555

1K -2

100K -1




9v DC

Step 2: Diagram



    • Indoor Lighting Contest

      Indoor Lighting Contest
    • Make It Fly Challenge

      Make It Fly Challenge
    • Growing Beyond Earth Maker Contest

      Growing Beyond Earth Maker Contest

    4 Discussions


    O.K., you're off to a good start, now it is helpful to explain what this circuit does, and also post your images of the build process.

    3 replies

    Since the author has not replied anything I will give you an explanation of the circuit.
    This is a monostable circuit based on 555 timer IC. The 555 timer basically has two modes of operation: astable and monostable.

    This particular circuit is a monostable, not retriggable. After the pushbutton is pressed and pin 2 (trigger) set to ground, output of the circuit (pin 3) goes to high logic state. The voltage of the high logic state equals to voltage supplied to Vcc pin (pin 8). Duration of the pulse produced on the output is given by an equation:

    t = 1.1 * R * C

    In this schematic it is resistor R3 (100k ohms) and capacitor C2 (100 uF), that are connected between pins 7 (discharge) and 6 (threshold).

    In this particular schematic, output pulse has duration of 11 seconds.

    After 11 seconds the output goes back to low.

    Since it is a nonretrigerrable monostable, the pulse cannot be prolonged by pushing the button again.

    Hope it makes sense to you. Have a nice day. :)

    Thank you for the kind of detail that was lacking, the 555 is truly timeless (no pun intended ;-)), an amazing bit of engineering since it's inception going back to the last century.