Pull up resistor and power supply to controLler

• Nov 17, 2016

• #1

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venkates2218

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In my project i used 1K resistor as pullup resistor for pic microcontroller on PORTB and enabled internal pullup resistor also...

is 1k is suitbale for pullup operation..?
Or i need to change the value...?

 

• Nov 17, 2016

• #2

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Okada

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Pullup resistor for what ? Button circuit ? You can use 1k. I use 4.7k to 22k.

 

• Nov 17, 2016

• #3

andre_luis

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venkates2218 said:

is 1k is suitbale for pullup operation..?

Click to expand...

Pullup operation for what ?

To drive a minimum idle current to some power device (e.g LED ) ?
To set a default state to a high impedance input (e.g MOS logic gate ) ?
etc...

 

• Nov 17, 2016

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venkates2218

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For push button

 

• Nov 17, 2016

• #5

Easyrider83

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For battey powered device you should care about leakege current. For other causes use Ohm's law, please.

 

• Nov 18, 2016

• #6

alexxx

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i used 1K resistor as pullup resistor for pic microcontroller on PORTB and enabled internal pullup resistor also...

Click to expand...

In this way you are parallelizing to resistors. Doesn't make sense. The internal pull-up should be sufficient.

 

• Nov 22, 2016

• #7

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venkates2218

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for battery powered circuits alone..?
Or we have to care leakage current in all forum power supply circuits..?

 

• Nov 22, 2016

• #8

KlausST

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Hi,

how is your "pull up" resistor related to "power supply" circuits?
It isn´t clear to me.

A simple drawing could clarify.

Klaus

 

• Nov 23, 2016

• #9

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venkates2218

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i dono know about it..?
Easyrider83 mentioned liked below,so i'm asking is their any relationship between the pull-up resistors and type of power supply..?
For battey powered device you should care about leakege current. For other causes use Ohm's law, please.

 

• Nov 23, 2016

• #10

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Okada

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You should save more energy in battery powered devices.

 

• Nov 23, 2016

• #11

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venkates2218

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sorry i can't understand your answer OKADA...
Can you explain it please..?

- - - Updated - - -

i'm going to use 7A DC 12V battery as power supply...
Is any problem will created due to pull-up resistors to battery..?

 

• Nov 23, 2016

• #12

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Okada

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Use 22k resistor in battery powered devices for pull-up resistor. When higher value pullups are used very less current flows. This saves battery current. If battery 150 mAh then you nned to save more current.

Say current will be flowing in the internal circuit. If 1k resistor is used with 5V then 5V/1k = 0.005A flows. If 22k resistor is used then 2.27 * 10^-4 A current flows.

I thought Li-Ion battery stacked to get 5V.

Assuming some current flows in the internal circuitary of MCU when button is not pressed and internal resistance is 0 and only pull-up resistance is considered.

Image 2. Assume the meters are inside the MCU.


1k resistor and 5V

current = 5 mA

Power in resistor = 0.025W

22k resistor and 5V


current = 227 uA

power in resistor = 0.001134W

 

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Last edited: Nov 23, 2016

• Nov 23, 2016

• #13

KlausST

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Hi,

i'm going to use 7A DC 12V battery as power supply...Is any problem will created due to pull-up resistors to battery..?

Click to expand...

even more confusing.

Is your pullup resistor connected to 12V battery? .. Or why do you mention battery voltage?

I don´t like guessing. If you are interested in an answer, then post a simple circuit drawing....

Klaus

 

• Nov 24, 2016

• #14

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venkates2218

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normal citcuit using pic micocontroller...
In that i'm using pull-up resistor for push button ..
If battery is used as powersupply means it will affect the battery life or something else...
Because by using pullup resistor we are shorting positive and negative power supply when the button is pressed....

 

• Nov 24, 2016

• #15

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Okada

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Pullup resistor value decides the current drawn from the battery. High resistance, lesser current and more battery life.

 

• Nov 24, 2016

• #16

alexxx

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Use the internal pull-up. It is tenths of KOhms. No external resisitor is required. Even for low power. External or internal, there will be power loss. But someone will press it for a couple of seconds and then he will release it. So it is not a big deal.