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Pull down resistor question

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Alfgan:
Hello everyone!

Should I place pull down resistor near button? And if I should, what nominal it should be?

boffin:

--- Quote from: Alfgan on August 27, 2019, 05:27:03 pm ---Hello everyone!
Should I place pull down resistor near button? And if I should, what nominal it should be?

--- End quote ---

Yes, perhaps, and maybe.  Depends on what you're using it for.

In some cases you don't need a resistor at all as what you're feeding may already have a pullup (or pulldown) resistor. 
Case in point, the Atmel processors used in an Arduino, have a pullup you can enable with INPUT_PULLUP(aka pinMode(2,INPUT_PULLUP); to enable the pull up resistor.  The only thing thing is you'll be hooking your switch from pin to ground instead, and your reading will show 0 when pressed and 1 when released, but that's easy in software.

Alfgan:
Thank you for information :)

So in the situation above I do not need pull down or pull up resistor?
This is a 555 dice and I want the dice to start when I press the button. I am not using arduino there.

Audioguru again:
It is obvious that a pulldown resistor parallel with the pushbutton would keep the circuit acting like the pushbutton was continually pressed. Then the 555 would keep the LEDs spinning continuously.
The transistor already has a pullup resistor (3.3M) that helps to turn it off as the 1uf capacitor discharges after the pushbutton is released.

Alfgan:
Oh thank you very much.

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