Author Topic: Pull down resistor question  (Read 1117 times)

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Offline AlfganTopic starter

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Pull down resistor question
« 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?

« Last Edit: August 27, 2019, 05:34:29 pm by Alfgan »
 

Offline boffin

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Re: Pull down resistor question
« Reply #1 on: August 27, 2019, 05:37:07 pm »
Hello everyone!
Should I place pull down resistor near button? And if I should, what nominal it should be?

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.

 
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Offline AlfganTopic starter

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Re: Pull down resistor question
« Reply #2 on: August 27, 2019, 05:47:15 pm »
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.
« Last Edit: August 27, 2019, 05:50:59 pm by Alfgan »
 

Offline Audioguru again

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Re: Pull down resistor question
« Reply #3 on: August 27, 2019, 06:01:40 pm »
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.
 
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Offline AlfganTopic starter

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Re: Pull down resistor question
« Reply #4 on: August 27, 2019, 06:22:09 pm »
Oh thank you very much.
 

Offline Damianos

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Re: Pull down resistor question
« Reply #5 on: August 28, 2019, 09:10:03 am »
The circuit operates with the resistance of a finger, that when touches the wires charges (partially) the capacitor and produces random results. If a button is used, then the capacitor will always be charged immediately to the battery voltage and the result will be more or less predicted.
 
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Offline AlfganTopic starter

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Re: Pull down resistor question
« Reply #6 on: August 29, 2019, 09:29:56 am »
Ooo oh okey thank you.
So if I made a PCB with a button, should I just solder wire in the button footprint place?
« Last Edit: August 29, 2019, 09:32:20 am by Alfgan »
 

Offline Damianos

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Re: Pull down resistor question
« Reply #7 on: August 30, 2019, 06:48:27 am »
If you use the PCB alone, make two pads that can be easily touched by a finger. If you will use a box for the circuit, bring two wires with the "naked" ends attached to the outside, in a way that the sharp ends do not harm a finger.
 


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