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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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Help understanding simple Arduino circuit from a datasheet example

I'm trying to use a water sensor in a new design, and I don't understand the example circuit that is given in the datasheet, even though it looks very very simple. I must be missing something. Any ...
Open_Hamster3337's user avatar
2 votes
2 answers
345 views

How long is it okay for pin to be floating during MCU startup?

I’m using an ESP32-S3 to communicate with a 5V-only LCD module with an i8080 parallel bus interface. To shift the levels, I’m using the SN74LVC8T245 bidirectional level shifter. This means I can both ...
Emil Eriksson's user avatar
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How to bias an input AC signal for active high-pass filter?

I have been trying to design a 2-way active crossover, with low-pass and high-pass channels. So far I got the desired frequency response but the transient response is not up to mark. Here is the ...
Sajil's user avatar
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Weird I2C Problems

So, currently we are having problems with the I2C Communications on our cabinet Each row on the cabinet has 5 boards which have 2 16bit io expanders each board has 32 devices and there are 4 boards in ...
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GPIO trigger and correct pull-up/-down resistors? Internal pullup deviates from recommended value

I have these devices: Sensor Keyence FS-N41P Camera Flir Blackfly S Controller Teknic Clearcore The sensor triggers the camera and the controller. The controller supplies 24V to the sensor. This is ...
Martin Henne's user avatar
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What types of outputs apart from Open Drain/Open Collector exist?

I am trying to grasp the idea of an Open Circuit/Open Drain, but I haven't been able to find, which other types of outputs exist ("Closed Circuits", so to speak). It would be helpful, if you ...
Andrew's Quest's user avatar
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How should I select the ohm values for pull-up and pull-down resistors in a device with a USB Type-C connector used solely for power

Good morning, everyone. I am exploring the transition of the receptacle from a micro USB connector to a USB Type-C. Initially, my plan included implementing both sink and source capacity. However, ...
condor12's user avatar
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Replace micro USB tablet connector with USB C

I'm considering upgrading my dad's old tablet, which currently has a micro USB connector. The issue arises from his habit of frequently misplacing the charger, and I'd prefer not to rely on an ...
condor12's user avatar
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3 votes
2 answers
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PNP transistor not pulling up completely : what is wrong in my schematic?

I cannot seem to make the schematic below work. As you will plainly see, the idea is to use the PNP as a switching device for a PhotoMOS (TLP354x). By switching SW1, Q1's base goes to the ground ...
VoltsAndNuts's user avatar
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ESP32 Boot Mode

I am using ESP32-S3-WROOM-1-N16R2 in my design. In ESP32-S3 development board schematic they connect boot pin GPIO0 with external switch. The reference image of dev board link is below: https://dl....
Kuralmozhi's user avatar
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SCL line Pulled Low all the time

I have made a custom PCB with nRF52840 and Three slave Devices(IAM-20380 Gyro), (ADXL372 Accelerometer), (VCNL4040 Proximity ) Sensors. All slaves are connected to one I2C Bus When I plug only power ...
Zunuran Nasrullah's user avatar
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2 answers
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How to calculate pull up resistor for Power Good Pin?

I am learning to design buck converter. And using LM70880-Q1 buck. There is power good pin is available. I want to make use of this pin. It is a open collector output that goes low if the Vout is ...
Virtualworld 's user avatar
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3 answers
176 views

Clarification about leakage current in IC

Datasheets usually specific pin leakage current for digital inputs in the Electrical Characteristics, which is generally in microamperes (µA) range. I understood from different SE posts that the ...
LoveEnigma's user avatar
7 votes
2 answers
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Why do the I2C pullup resistors in the datasheet differ so much from my calculations?

I´m using the LSM6DSR accelerometer/gyroscope from ST on a project. Looking into the application hints, it suggests using a 10k resistor as pullup for SDA AND SCL: Since I´m using another slave (...
DMinatto's user avatar
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Ground detection circuit

I'm designing a circuit containing a button with a pull-up/pull-down logic depending on whether I'm grounding a header. The button triggers a GPIO that will detect if the header is grounded thanks to ...
Bibibou's user avatar
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Does my GPIO Expander have a floating pin? [Button and pull-up resistor]

I am using GPIO expanders (MCP23017) for an array of buttons. Each button is connected between GND and an input pin of the expander. I've enabled the 100k internal pull-up resistor on the MCP23017 (...
Nate.Olson's user avatar
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PIC reset pullup

I'm trying to repair a "Flexineb E2" veterinary nebuliser for somebody, it holds a charge and works plausibly well if the battery connection is briefly interrupted but will not power-on if ...
Mark Morgan Lloyd's user avatar
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Does this design cause floating input?

I started investigating this circuit. The circuit is used to detect another PCBA when it is plugged in as the signal IN# and sends the signal IN#_BUF to the microcontroller. The issue is sometimes the ...
WUP's user avatar
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2 answers
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How do I use a pull-up resistor to trigger a relay?

I have a 12v automotive electrical system that has a pressure switch that switches at 40psi. It is normally closed to ground (low pressure), and goes open when switched (high pressure). The switch ...
Chris S's user avatar
2 votes
2 answers
228 views

How big a pull-up resistor is needed to pull up an internally pulled-down GPIO (ESP32-C6)?

I'm feeding a BCD diode matrix of switches with Vcc at 3.3 V and running the BCD outputs into GPIOs on the ESP32-C6. The plan is to set each GPIO input to internal pull-down so I can pull it up ...
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Alternative to pull-up resistor

I am building this AND gate, and I managed to get it to work properly. However, I had to increase the value of the pull-up resistor to 3 megohms which is too big for what I need. However if I don't ...
Jake's user avatar
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3 votes
3 answers
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Multiple NAND gates built with transistors linked together

I am trying to build a full adder with NAND gates. I have a transistor implementation: I am getting the wrong output voltages for Cout and S; is there a way to fix this? Is it my resistors that have ...
Jake's user avatar
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Connecting an open-collector output to a transistor base using a single pull-up resistor

I have a Hall-effect sensor with an open-collector output rated for max. 25 mA. This sensor will be used to switch an NPN transistor powering a 12 V LED strip. The load is 300 mA. Could I get away ...
Joshua Dotson's user avatar
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1 answer
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Esp32 INPUT-pullup

I have an enable pin that i want to drive high always except when a limit switch is closed, and at the same time I want to monitor the state of the limit switch So is that possible with input_pull-up ...
hjeij2000's user avatar
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1 answer
104 views

Do I need pullup resistors for a voltage level shifter driven by a push-pull GPIO output?

I need to shift a 3.3V, push-pull SPI bus from my STM32F3 controller up to 5V to drive a MAX7219 LED controller. To do this, I aim to use an NVT2022 level shifter, datasheet here. The first paragraph ...
kiryakov's user avatar
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2 answers
222 views

ECP5: Determining max current an FPGA pin can sink from datasheet

I have a circuit where I want to drive the CS# input on a SPI flash chip from an output pad on an FPGA. The flash IC's datasheet recommends putting an external ...
jemalloc's user avatar
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3 votes
4 answers
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How can I read the value of an open drain pin connected to an LED

I'm developing a circuit with a charger inside. The charger has 2 STAT pins that indicate the functionality of the board (charging, standby, fault, etc.) As the datasheet suggests, I've connected two ...
Filo_Gold's user avatar
1 vote
1 answer
195 views

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 ...
AlphaBob's user avatar
4 votes
2 answers
291 views

What causes a negative voltage dip on the collector of common emitter NPN circuit at turn-off?

Circuit diagram: simulate this circuit – Schematic created using CircuitLab Observed waveforms: (Yellow: 3.3V square wave in, Magenta: Collector output) When the input square wave goes low and ...
Unimportant's user avatar
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2 votes
4 answers
384 views

Pull-down resistors and ground

Please help me something that I don't understand: Why is there a need for pull-down resistors in the circuit below with push button if the ground has already zero voltage? This is the only thing I ...
Voloo's user avatar
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0 votes
0 answers
22 views

Power sequencing: enable signal hold below threshold if asserted after supply

Short version: When I power my PCB and the SYS_EN signals at the same time, all voltage rails turn on. If I first power the PCB, then pull high the SYS_EN signal, the 3.3V and 1.8V rails don't turn on....
Sandro's user avatar
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1 vote
1 answer
114 views

Custom i2c with Arduino UNO

For educational purposes, I would like to write my own i2c protocol. Is it possible to write a custom i2c library to communicate using regular ports, or should I use the SCL and SDA ports? Can I mimic ...
Anton Tsvayer's user avatar
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1 answer
526 views

MAX3362 RS485 IC connection with ESP32

I am using MAX3362 RS485 serial data transfer IC with ESP32. Marked pins 1, 2 and 3 are connected to GPIOs of ESP32. Do I need to add any additional pull-up resistors or some termination resistors or ...
Zunuran Nasrullah's user avatar
2 votes
3 answers
407 views

Why AP331A comparator doesn't work without pullup?

I was designing a PCB and had to include some kind of analogue signal peak detector, so I used comparator to get +3.3V when signal is above 2V and 0 when signal is bellow 2 V. I chose AP331AWG ...
Dominykas's user avatar
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2 answers
152 views

Can a voltage divider be used to safely lower pull-up voltage?

I'm working with an LTC2950 pushbutton on/off chip that's meant to toggle the enable pins of voltage regulators based presses from a momentary pushbutton. The LTC's enable pin is open drain and is ...
E.HP.S's user avatar
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1 vote
2 answers
131 views

Thoroughly confused about open drain

I've been reading a tutorial on open drain and I'm thoroughly confused. First, the terminology makes little sense. How can a resistor pull up or pull down current when its job is to resist current? ...
user148298's user avatar
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3 votes
1 answer
391 views

Datasheet says pull up/down resistors are not necessary, but application of part uses resistors?

I am using a TPS2546 in a USB charging hub, and I'm basing it on a preexisting design I found online (link to writeup for design). In the schematic for the hub design the ILIM_SEL, EN, CTL1, CTL2, and ...
Cole Morrel's user avatar
4 votes
2 answers
847 views

MAX485 module, pull ups for RX and TX

I recently bought the below RS485 module. I see from the schematic they use pull-ups on pins 1 and 4 (TX and RX), can someone explain why are those pull-up resistors needed (R1 and R4)? Secondly, pins ...
JoeyB's user avatar
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2 votes
4 answers
2k views

What are pull-up resistors for and how are their values calculated?

I have some questions related to pull-up resistors. Just trying to understand in depth here. Why do we use pull-up resistors on the input pins of a microcontroller? Can I directly connect GPIO input ...
Wajahatulla Sharif's user avatar
3 votes
1 answer
195 views

A pull-up resistor increases the low side of a signal, how can I counteract it?

I have an ebike computer that has two inputs that accept square wave signals. The range is 0-5V. One of the inputs has no pull-up/down resistors on it. When I hook up a device producing signal, the ...
Nicolay Doytchev's user avatar
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0 answers
103 views

Need help with MAX31865

I am trying to program an ESP32-S3 microcontroller to write and read the registers of a MAX31865 IC over SPI, but I cannot get anything meaningful out of the device. The following image shows the ...
Marcell Juhász's user avatar
5 votes
3 answers
1k views

When you have a pullup resistor, does the system consume power?

If you have a pullup resistor setup: Image Source: Sparkfun - Pull-up Resistors If the button is open, is voltage and current constantly being drawn through the input pin or does the high impedance ...
Thomas Stokes's user avatar
0 votes
3 answers
214 views

Do I have to use pull up/down resistor with switch with common terminal?

I have seen some examples why we need to use pull up/down resistors, but do I need to use it if I use switch with common terminal? If I have the schema like so, do I need to use the pull up/down ...
krystof18's user avatar
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1 vote
3 answers
213 views

Pull-up resistor is running slowly (inverting MOSFET circuit)

There's a problem with my fan control circuit. It works well, but when I first power up the circuit, the fan runs for about 0.2 seconds. The reason seems to be the time until the pull-up resistor is ...
KimJiHoon's user avatar
4 votes
7 answers
2k views

How can I control PNP and NPN transistors together from one pin?

I'm trying to understand how it is possible to control a PNP and a NPN transistor simultaneously from one controlling pin. My issue is that when the INPUT pin is left floating, the transistors drive ...
AKTanara's user avatar
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0 votes
1 answer
71 views

Battery isolation circuit with inverted logic

I asked a question some time ago in regards to preventing back charging my back-up battery question. I was just using a diode, but a circuit was suggested for more protection. It doesn't lend itself ...
Feynman137's user avatar
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2 votes
5 answers
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"Pull-up" and "pull-down" or "push" and "pull"?

I thought about this question when I read an interesting comment by @Simon Fitch in his answer. In the complementary amplifier stage, in total there are three "pulling" elements - Q2 is a &...
Circuit fantasist's user avatar
1 vote
1 answer
357 views

How to choose pull-up resistor values for level shifting circuitry for serial communications

I recently joined a new project where two ESP32-WROOM-32UE modules on separate circuit boards talk to each other via the UART pins. The distance between the two boards is roughly 1 meter of cable ...
user2218339's user avatar
1 vote
1 answer
62 views

Confused by i/o expander datasheet note re internal pull-ups

The inputs on the NXP PCAL6524 i/o expander can be configured with internal pull-up or pull-down resistors. The datasheet states, "External resistors are required for inputs... that may float. If ...
Slothrop's user avatar
2 votes
2 answers
152 views

Debugging a problematic old TTL pull-up that's not pulling up

I am trying to bring back into operation a late-70s disk controller board (all 74xx TTL). I'm stuck trying to figure out why a small pull-up network is resulting in a far out of spec voltage not doing ...
BZo's user avatar
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