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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2 answers
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Pull up resistor why is it low when switch is pressed

When the switch in a pull up resistor is pressed why would the voltage in the pin be read as low? wouldn't closing the switch also connect VCC to the ground? wouldn't that mean that the voltage at the ...
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5 votes
1 answer
473 views

Why do we connect unused (always low pins) pins to GND through a resistor instead of connecting it directly to GND?

I have been reading the datasheet of RV-3028-C7. Everytime it talks about a pin that might be unused in a certain scenario (should be logic low), it instructs to connect the pin to ground through a ...
0 votes
0 answers
51 views

Maximum resistance on P-MOSFET gate pull-up

I have a P-MOSFET between my lithium battery and load. The P-MOSFET will only conduct if the battery's voltage is above a certain threshold to prevent over-discharging. The circuit is as shown below: ...
1 vote
0 answers
32 views

Cannot handle open collector output

I have a sensor powered at 24VDC which has an open collector output The output of the sensor (it is a PIR sensor), goes from 15Vdc when nothing is detected, and 0.7 Vdc when it detects some movement. ...
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1 vote
6 answers
172 views

Why are Arduino pins configured as inputs more like a source than a sink?

I've been using Arduinos for years but one thing I have just taken for granted without understanding is why, for example, in a simple button circuit using the internal pullup, you connect the button ...
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0 votes
3 answers
114 views

Problem with SN7407 output

I'm carrying out an experiment using an SN7407, which is an open-collector output buffer. The use of this IC is to make the pulses (PWM) coming from a DSP (~3.3 V) be sent to a gate-driver circuit (~...
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2 votes
1 answer
129 views

How does a pull-up resistor affect an RC low pass filter? Are two resistors necessary?

I'm using a low pass filter and a Schmitt trigger buffer to filter the output of a rotary encoder. I have included the manufacturer's suggested circuit as well as my copy of it for sake of referencing ...
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1 vote
3 answers
112 views

GPIO with no pullups or pulldowns

I have a SPDT switch connected to a GPIO pin on an nRF52810 microcontroller. The switch has two positions: Shorts the GPIO to GND Shorts the GPIO to V+ The switch is used to toggle a software ...
3 votes
2 answers
367 views

What is the point of configuring an output as "push-pull" and "pull-down" at the same time?

In CubeMX, there is still "pull-up" and "pull-down" options listed for an output while that output is already configured as "push-pull". How does it make sense to ...
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1 vote
0 answers
43 views

Capacitance/length limitations when daisy-chaining microcontrollers

I'm doing a daisy-chain of microcontrollers, with a half-duplex bidirectional line going from DOUT/DIN ports. I was thinking of doing tristate for the ports, and have a pull-up resistor connected to ...
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2 votes
2 answers
228 views

What is the voltage at this pin when it is internally pulled high?

I am using a PHY that has internal pull-ups and pull-downs on certain pins. On this particular pin, there is a pullup that the datasheet says can range from 33 kΩ to 93 kΩ. For the entire range, I ...
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1 vote
4 answers
139 views

Understanding pull-up/down resistors for a GPIO pin

I'm a total beginner, trying to find my way through basic electronics... I went over some written material and YouTube courses, but there is something I don't think I get right. Consider my case - I ...
0 votes
4 answers
102 views

Which one is better to use for micro controller input mode? Pull-up or pull-down?

As you know it's better to keep micro controller in "Sink" mode instead of "Source" of energy because it keeps micro controller safe and stable. For the input mode of an AVR (or ...
1 vote
1 answer
91 views

Open-drain output using N-channel MOSFET in addition to pull-up resistor

I'm trying to understand a design in an evaluation board and I need some assistance. In the above schematic, the PG output pin is open-drain so it requires a pull-...
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0 answers
62 views

ESP 01M LED circuit

I designed a small LED board using an ESP 01M. At first, the 5mm LED was working as I wanted. Sometimes the processor was reset, so I plugged a capacitor into the inputs and outputs of the AMS1117 and ...
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2 votes
1 answer
134 views

Pull up and down resistors at the same time

I have an I2C circuit with a 4.7 kohm pull-up resistor for each line. I think it might be a too strong (too small in value) resistor and the data isn't read properly. The processor I'm using has the ...
3 votes
3 answers
629 views

Do I need a pull-up / pull-down resistor to sense 12 V on the 12V_IGN rail in an automobile?

I'd like to start / stop a piece of software running on an in-car computer depending on the 12V_IGN rail going on resp. off. This happens when the ignition switch goes in / resp. out of position RUN. ...
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0 votes
1 answer
65 views

Connecting Arduino to Keithley external trigger

I need to connect digital output pin of Arduino Uno to Keithley DAQ6510 digital multimeter external trigger input. Both are utilizing 5V TTL logic. Now when I measure the voltage on external trigger ...
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0 votes
0 answers
86 views

How to Use ESP32's Input Only Pins with Keypad Library

I am tring to use 1x4 keypad with ESP32. I am using this keypad and this ESP32 (30 pins) also I am using this keypad library I have only free those pins 14,15,34,36 (VN) ,39 (VP) on ESP32. the others ...
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0 votes
3 answers
100 views

Output level of LM311 comparator

I am simulating the circuit above in LT Spice, where a LM311 (a LT1011 is simulated, but should be largely equivalent) is used to transform a (noisy) sine wave signal into a square wave. Value of R5 ...
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4 votes
3 answers
173 views

What does a pull-up or pull-down resistor actually "pull"

What does a pull-up or pull-down resistor actually "pull"? What does "floating" value mean? What is "floating"? Eg. in this picture, if there is no 10K resistor then the ...
0 votes
2 answers
28 views

explain high and low state

I have a TP4056 module (datasheet: https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf). It charges a 18650 cell. According to the datasheet : (Pin6): Open Drain Charge Status ...
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3 votes
1 answer
217 views

I2C maximum value of pull-up resistor (explanation)

This is more of mathematical problem, but I think there is an electrotechnical engineer that can help me. So I was reading about I2C pull-up values in the Texas Instruments SLVA689 I2C Bus Pullup ...
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0 votes
1 answer
50 views

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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0 votes
0 answers
101 views

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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0 votes
2 answers
67 views

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 ...
0 votes
3 answers
144 views

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 ...
0 votes
1 answer
61 views

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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1 answer
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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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-1 votes
1 answer
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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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4 votes
4 answers
843 views

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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-1 votes
1 answer
53 views

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 ...
11 votes
3 answers
1k views

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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0 votes
0 answers
62 views

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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1 vote
2 answers
116 views

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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1 vote
0 answers
76 views

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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0 votes
2 answers
133 views

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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1 vote
1 answer
71 views

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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3 votes
3 answers
505 views

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 ...
0 votes
2 answers
748 views

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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1 vote
2 answers
179 views

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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5 votes
2 answers
568 views

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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0 votes
1 answer
51 views

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
1k views

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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0 votes
1 answer
112 views

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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1 vote
2 answers
60 views

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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0 votes
2 answers
137 views

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 ...
0 votes
4 answers
145 views

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 ...
0 votes
2 answers
134 views

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 ...
1 vote
1 answer
97 views

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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