Questions tagged [pullup]

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

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Pull up / pull down resistor value

Wanting to calculate the value of the pull down resistor for a 555 trigger. For the formula should I use the typical or max trigger current (typ = 0.5 Max = 0.9 μA). I want the calculated value not an ...
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IMVP9 Controller VID/SVID protocol PU resistors

I'm using MP2940 IMVP9 Controller for VCCIN (CPU Power Rail) and VCCIN_AUX (PCH Power Rail) for a motherboard that includes Intel Tiger Lake UP3 Processor. VCCIN Controller uses SVID protocol and ...
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Should I use a resistor in series when connecting a pin to logic level high?

I'm trying to design a circuit with MAX8934AETI+. I'm confused about how to connect a pin to logic level high. For example, pin 6 in the picture below is meant to be connected to logic level high to ...
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Do circuits with pull up resistors waste more electricity than circuits with pull down resistors?

A pull up resistor provides a constant voltage (and therefore some current) to an input pin on arduino. https://learn.sparkfun.com/tutorials/pull-up-resistors/all A pull down resistor connects an ...
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Is a pull-up on open drain required when output is not used?

On a LTC3886-1 I can read this: I see that all open-drain outputs are tied to VDD on the following application schematics: Is there a reason why pull-ups seem required when the output is not used?
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Can I use a very large gate resistor to open an N-MOSFET?

I can turn on/off an AO3400 even across my body by touching the gate with my hand and the +/- pole of a 3V battery with the other, and it stays on even if I leave my finger by the gate capacitence. ...
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Op-amp burns out [closed]

On my PCB the input of the op-amp is shorted to VCC (28 V) or GND when the op-amp burns out (it happens a lot). In addition I want to add protection components on the input of the op-amp; if the op-...
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Switches with internal pull up at microcontroller

I'm trying to design a circuit that will detect if the normally closed switch is opened. The internal pull-up resistors in the microcontroller will pull the signal high, so the signal pin will always ...
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How to connect multiple dev-boards through I2C communication [closed]

Hi I am trying to build the circuitry having the devboards for the sensors like AHT21, GY521, DS3231 but the main problem is Each one of them has their own I2C Pull-up resistors if I connected them ...
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Pull-up and pull-down resistor on one trace

Does it ever make sense to have both a pull-up and a pull-down resistor on the same trace? Background: I'm designing a backplane to follow the OpenVPX guidelines and I saw this rule Rule 7-20: The ...
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How can I suppress transient HIGH signals in an opto-isolated digital circuit with pullup resistor

simulate this circuit – Schematic created using CircuitLab I am recording an opto-isolated signal using the opto-isolated output described here: http://softwareservices.flir.com/BFS-U3-04S2/...
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MCU GPIOs internal pull-ups with external voltage divider

I am designing a board based on STM32F7 with a dozen of Digital inputs that need to be 12V tolerant. On the first design, I was using a voltage divider to have the right logical high detection when ...
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Erratic pull-up on ESP8266 UART

I have a logic-level UART connection between an STM8 and an ESP8266. The STM8 Tx goes to the ESP Rx through a 1 kΩ resistor, so that I can override the STM8 signal when I want to program the ESP8266. ...
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I2C slave pulls down SCL while doing nothing

I have an MCU (Texas Instruments tm4c123gh6pm) in which I have configured an I2C slave device. I have taken 3.3V from the MCU pin that provides them and connect them to two 4.7 kOhm resistors (to make ...
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I2C SCL goes low if using MCU GPIOs as pull-ups

I have an MCU (tm4c123gh6pm) in which I have configured an I2C slave device. At the moment I don't have resistors to wire the required pull-ups, so I want to use two of the MCU's GPIOs for this ...
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Why would a digital input require a pulldown instead of a direct connection to the input voltage?

I've seen datasheets for certain ICs recommend using a 100 kOhm (or so) pulldowns or pullups for setting configuration inputs. What could be a typical reason for this? Normally I would just tie the ...
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USB pull-up in STM32F103 (D+)

I've got pretty quick question as a beginner in STM32 MCUs. I design my own PCB board for STM32F103C8T6 uC with a couple sensors (connecting via SPI and I2C). I want to include also an USB connector ...
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SD card socket just need to wire with pull-up resistors?

I have a question about Micro SD card and STM32F446RE wiring issues. I saw this schematic from ST forum. I would like to ask, when I wiring STM32F446RE with SD card socket (I mean connection part), ...
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2 answers
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Pull-up resistors on I2C port

Hi everyone, I am confuse about I2C pull-up resistors. I use 4 I2C sensors. I am not sure is it true that pull-up resistors count. I use every sensors for pull-up resistors. If I use just one I2C port ...
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Why is the push button state taking too long to in the program?

I wired up the circuit using a pull down resistor of 10KOhm according the schematic provided. I'm using Jetson Nano (MCU).The push button (DF Robot PB) has three wires, +ve,-ve, and signal, pin 1,pin ...
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2 votes
3 answers
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Do you need a current limiting resistor on an enable pin?

I am using MCP16312-E/MS buck regulator and need the component to always be on. I am therefore connecting the enable pin to the Vin supply. Do you need a current limiting resistor? Whilst the resistor ...
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GPIO is too senstivie

I've encountered a weird problem and I'm not sure whether it's actually a problem or everything's ok. But going straight to the point. I've got Raspberry Pi Zero W, one of its pins is configured as ...
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Reading the input from a relay's NO output over 12 meters

I want to read the input from my driveway gate beam using an Atmega32. I know the gate beam is powered with 12V DC which I get from the driveway gate motor's battery. The beam also has three outputs, ...
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How does a pull up resistor change a voltage divider calculation?

I am using this proximity sensor with a raspberry pi. the sensor outputs a 24V signal when triggered, which I need to step down to 3.3V using a voltage divider so as to not blow out the pi. The ...
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Buttons in parallel - short circuit? [closed]

I encountered a problem while trying to use 21 buttons at the same time. Initially, I did not take into consideration that they could be pressed all at once. And while measuring the resistance I ...
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Are pull up and pull down resistors required?

I am trying to design PCB with a W5500 and an RP2040. I have some questions. I read the W5500's datasheet. In this photo, it says pull-down and pull-up for some pins but in the example design they ...
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1 answer
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How to interface MCU with open-collector output?

I have a 3.3VDC microcontroller (based on Nordic nRF52840) with digital inputs which I need to interface to a device that outputs slow pulses (1 second) via an "open collector output". The ...
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2 votes
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Powering an ATtiny85 from the pull-up resistor of another device

I have an interesting design challenge. Reed switch S1 is feeding pulses at a maximum of five per second into a 3.3 V microcontroller input. I want to halve the pulse rate. I don't have access to the ...
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On what factors does the I2C pull up resistor values depend upon

I was reading this Article regarding the pull up resistor calculation. I understood that the value of the pull up resistors depend upon the currents, the supply voltage and the Logic Level voltages ...
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Using shared pull-down resistor or providing pull-down for each mosfet

There are some P channel and N channel mosfets which operate as swiches in figure 1. Also, there is a pull-down resistor for each mosfet which prevents the mosfet's gate being float when the VCC is ...
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Why does the TCA8418E datasheet ask to connect all pins to Vcc using a pullup resistor?

I am trying to use the TCA8418E I2C Controlled Keypad Scan IC With Integrated ESD Protection. On page 3 in the pin functions table it says to connect SDA and SCL to Vcc using a pullup resistor. Do I ...
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2 votes
3 answers
553 views

I2C pull-up resistors and voltage

I have a sensor that I'm trying to read via I2C, but I have some issues with the pull-up resistors and what voltage they would be set to. My host computer is the Arduino Nano Every while my sensor is ...
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2 answers
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Why are pull-up inductors biasing the power amplifier output of radio transmitters chips needed?

I have seen many designs where the antenna/PA output is fed DC voltage through an inductor. Why not leave it out and feed the DC bias directly? It is L1a in the diagram below: There are some values ...
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Will a blocking diode in series with pull-up resistors negatively affect the I2C bus?

I'm using an I2C EEPROM IC in a project to store configuration and settings for a Teensy Microcontroller, and I'm currently trying to work out how to achieve reprogramming of the settings. I plan on ...
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Using a pull-up resistor and considering rise time for IC input

I have a FPGA based design in which the FPGA is interfaced with several ICs. The I/Os of the FPGA and most of the ICs are 3.3V, except from one where the I/Os are 1.8V. While there is no problem for ...
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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 ...
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Can a pullup be placed on the LED input of an Optocoupler?

The diagram is a minimum example R1 is the series resistor for the optocoupler's LED. R2 is a pullup that's absolutely required there for other components. Will the pullup be overcome by the ground ...
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BNO055 No Sensor Data but Address Can Be Found

Hello I'm trying to use the BNO055 sensor in my project. It's hard for me to get the sensor as a seperate IC so I buy BNO055 modules and take the IC's from the modules by heating with hot air. In my ...
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I2C Level Shifter pull up Calculation

I am using PC9306(https://www.ti.com/product/PCA9306) for one of my project with Vrfe2=5v and Vref1=1.8V.Below is the block diagram. My CLK is running at 100Khz. I got the equations for pull up ...
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Connecting 1-Wire DS1820 with 5VDD - needs voltage divider?

I am trying to use a DS1820 Temperature Sensor on 5V VDD with an ESP32. Now I have read on different websites that I need a pull-up (4k7) for the data line but some state that it's fine to put the ...
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Should a pull resistor be on the main MOSFET or at the driver?

I want my MOSFET to be initially "off" by default. I can’t decide whether to place the pull resistor on M1 or M2 (pull up at M1 and pull down at M2). My typical instinct would tell to ...
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Half of voltage on GPIO when using external pull-up

I added a pull-up resistor to GPIO in order to use the reed switch. You can see the wiring in the picture I attached. It works but I'm confused why when I wire multimeter to PB0 and GND it shows about ...
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3 votes
2 answers
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Math behind pull-up resistors

I have a question about the the math behind of pull-up resistors and how they work. I don't have any experience in the Electric Engineering field so it's probably a basic question. I saw many ...
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2 votes
3 answers
501 views

10 resistors from VCC to data [duplicate]

I realise that this has been asked elsewhere, specifically: That's actually a wiring diagram (and some of the folks around here call them cartoons) but it will suffice as the schema can be seen since ...
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How do open-drain I/O pins work on a PIC16 microcontroller?

I'm trying to understand how to operate an open-drain I/O port on an older PIC (PIC16F1718.) My goal is to use it for bit-banged bidirectional open-drain I2C communication. I know how to enable and ...
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LS7220 passcode IC

I bought the LS7220 IC which is designed to check passcodes. For some reason, the pin 8 Lock Status Output does not illuminate the LED when I connect the power, and when I bridge the VCC in sequence ...
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Pull up resistor in SPI Flash?

while going through one schematics , I found that we are using Pull up resistor for MISO, MOSI, CS in SPI connection between IC and Flash? Why we are using pull up for SPI connections? Is it any ...
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Pull-Up resistor for a 74LVC1G06 Inverter

As part of dual mode display port design, Pin13 goes to 74LVC1G06 inverter input (see U89): in case where I want to choose only HDMI I need to connect a pull-up to DP_0_PIN13. from wikipedia : "...
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2 answers
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Confused about pull-up resistor

I'm a software guy trying to implement a 1-wire interface. I have modified a USB-to-UART device as indicated here, but I don't understand the "pull up" resistor concept. Googling "open-...
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2 votes
1 answer
193 views

How stable is Pull-up / Pull-down resistance in newer microcontrollers like SAM D21?

I'm working on a low power design using SAM D21 microcontroller (Adafruit Feather M0). I would like to take advantage of configurable I/O and have it normally in high impedance state, but reconfigure ...
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