Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [pullup]

A Pullup Resistor brings a line up to a voltage (Typically VCC), while allowing the line to be pulled low.

A Pullup Resistor brings a line up to a voltage (Typically Vcc), while allowing the line to be pulled low. Encountered in Open-Drain or Open-Collector systems, including I2C.

Threads with useful reading

A question on pull up resistors (switch with a pull-up resistor)
How do I calculate the required value for a pull-up resistor?
Is there a correct resistance value for I2C pull-up resistors?

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Pull-up resistor clarification

I'm quite new to electronics and I'm having a hard time understanding the "pull-up resistor" principle. I have read a lot of articles about that, and I think I've got it but I'm not 100% sure so I have a question. In this article, after the first…
ssougnez
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Why do we need a pull-up resistor if we can just make a short to the power source?

I saw the term pull-up resistor being mentioned everywhere, but I haven't grasp the reasoning behind its use. For example, I saw one in the book Practical Electronics for Inventors, in this schematic for 555 timer arranged for monostable operation.…
Andree
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Pullup resistor value based on current sinking capabilities

Actually a lot simpler question than the title would suggest. I'm planning on using a SN74AHCT125 quad buffer as a logic-level converter from 3.3V to 5V. I only need two of the four inputs. As per the function table, when \$\overline{OE}\$? input…
CircularRecursion
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Why are pull-up resistors not drawn this way?

So, I've always been using a pull-up resistor in the configuration that usually appears in textbooks but I can't tell why it isn't drawn in another way. So, basically a pull-up resistor is usually used to prevent a direct connection between ground…
medwatt
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Identifying the 4 pins on a 4-pin connector - Is this the correct approach?

Identifying the 4 pins on a 4-pin connector Is it possible (and safe for the electronics with the power OFF) to identify the 2 signal pins on a 4-pin connector, located on a mother board, by checking resistance between the suspected signal pins and…
AlphaBob
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Are pull-up resistors necessary for the TUSB320HA's EN pin if it's never set low?

The TUSB320HA IC has a pin named EN that needs to be set high to enable the chip. According to the datasheet: VIH_EN, the voltage needed to set EN high, should be between 1.05V and 3.65V IIH, the high-level input current, should be between -20uA…
ide
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Calculating pull-up resistor value for CD4078

How can I determine the proper value for a pull-up resistor that's being used as an input to a CD4078 when the datasheet doesn't mention anything about input impedance? I'm trying to minimize power usage since my circuit will be powered by a…
Joe Sylve
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Pull up to 5V on a wire that may occasionally see 60V

I have a wire that either floats - that's when I want to pull it up to 5V - or it may see up/down to +/-60V applied to it - and that's when I really don't want it to be connected to the 5V rail. Problem is that I can't figure out how to make a…
avg
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A question on pull up resistors

I'm wondering why pull up resistors in text books are told such that they pull up the voltage to \$V_{CC}\$. Here is a diagram: When the button is open what will be the input voltage to the micro controller? \$V_{CC}\$? No voltage drop at \$R_1\$?
user16307
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LM311 Pull Up Resistor

If I use an LM311 Comparator, then we are required to connect a pull up resistor at the output. Does the square wave output depends on the value of the voltage the resistor pulls up to? Would it be that if i had a 5V on the pull up, then the output…
Sherby
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The role of pull-up resistor to allow inverted logic high/low voltage without wasting electric current?

Logic input in logic circuits can be on, off, or disconnect. In the last case, there is "floating logic" issue, inductance and electromagnetic noise causes current in logic parts that may be missintepreted as "on". For this reason, logic circuits…
LearningBasicComputerScience
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THVD1550 Transceiver

I got this IC in my circuit and I'm wondering if I could hook up a pull-up network to it, in the following way: Since it's an RS485 transceiver, the input to it is differential. I need to know if I can input a non-differential voltage as an input to…
Daniel Korbin
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CMOS Output Sensor with a pull up resistor

The MH251 Hall Effect Switch has a CMOS output, which doesn't need a pull-up resistor. The typical application circuit on the datasheet is as shown: Since the same design will also be used by other sensors that require pull-up resistors. I am…
RoastDuck
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I2C pullup resistors interfere

I have two modules that uses I2C and both connected to an Arduino. one of them have two 10K pullup resistors. The other one is an 16X2 LCD I2C: I couldn't find an schematic for this module but tracked the connection with DMM. Connecting the LCD I2C…
ElectronSurf
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Are external pullup resistors required D I/O pins on RN4870/71?

Are external pull-up resistors required on RN4870/71 for pins like "P1_1"? The datasheet mentions D I/O pins being "pulled-high", is it pulled high with internal resistors or programmatically from the microcontroller it's connected to or are…
be-ee
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