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I have a question about the wiring a 555 Timer in Monostable Mode? Answered

Hey all I am relatively new to the world of electronics. I have been learning about the different modes of the 555 timer chip because I would like to incorporate it into an upcoming project. I made a circuit and did the calculation so that once a button was pushed, an led would stay on for 5 seconds and then go off (a one shot timer). Everything worked ok accept I noticed that when hooked the battery up to the bread board (my last step of the build) the LED would turn on stay on for 5 seconds then shut off.  Is there a way to wire it so that when power is initially applied to the circuit it doesn’t trigger the timer? In other words the only thing I want to trigger the chip is a push of the button, nothing else! please let me know if this make sense. Thanks!

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Josehf Murchison

3 years ago

Yea the 555 timer will do that on power up when used as a oneshot if your button goes to ground. Try a oneshot circuit where the button goes to vcc.

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steveastrouk

3 years ago

Usually because pin 2 isn't pulled up, put a 4.7k resistor to the supply and pin 2.

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Mpc1055steveastrouk

Answer 3 years ago

Steve, This is the schematic I am using, shouldn't the 10K resistor due the job that the 4.7K that you are calling for do?

Oneshot.JPG
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Mpc1055steveastrouk

Answer 3 years ago

I do have on on there, I must have wired it wrong! Thanks for the advice!!!!!