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Questions tagged [pulldown]

A pull-down resistor brings a line down to a voltage (typically ground potential) when the line isn't being driven to a specific voltage. It prevents the line from "floating" with an unknown voltage on it.

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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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1 answer
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Question about DC pin in USB C module. Is it possible to connect two USB C and Micro USB connectors in parallel to charge the same battery?

Good morning everyone, I received help from several members of this page regarding my goal of adding a USB-C connector to a tablet that already has a micro USB connector for charging. After ...
condor12's user avatar
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Are the data pins necessary on a mini USB connector used only for charging a tablet? Is the ID pin used for OTG?

I have an older tablet, and I plan to replace the charging-only micro USB connector (which does not transmit data) with a USB-C connector. However, upon examining the pinout, I noticed that the two ...
condor12's user avatar
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0 answers
49 views

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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1 vote
1 answer
148 views

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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33 views

Why is pull-down resistor on low-pulse triggered relay input not working?

I have a low-pulse triggered latching relay board (datasheet for individual relays, link to board). Whenever I plug-in, or un-plug my Arduino Nano's USB cable the relay changes state (sometimes ...
Goulash's user avatar
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1 answer
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Inverting Op amp do i need a pull down resistor

So im currently working on a circuit and im not too familiar with inverting Op amps and therefore am asking for some help below is my circuit its the latter half of the circuit and just wondering if i ...
jarred coles's user avatar
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31 views

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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35 views

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
0 votes
3 answers
158 views

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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1 answer
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Loop in Arduino LED circuit, with push-button for mode switching, stuck when moving to Mode 3

I have been working on an Arduino project: 4 LEDs connected on a breadboard, with series-parallel circuits, that are being controlled by push button. The desired behavior is to start in OFF mode, and ...
Dio B.'s user avatar
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2 votes
2 answers
226 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 ...
KJ7LNW's user avatar
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0 votes
1 answer
130 views

Combining voltage divider, pull-down resistor and low-pass filter in analog sensor signal

I am integrating a KP236N6165 analog absolute pressure sensor from Infineon. They recommend the following circuit : My microprocessor which receives the signal uses 3.3V logic and is not 5V tolerant ...
Tommy95's user avatar
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1 vote
1 answer
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TC4420 MOSFET Driver Output Latching Behavior

The TC4420 push-pull MOSFET driver seems to latch its output on if the low input signal isn’t pulled to ground. The signal I am using for the input is purely an on-off signal where the off part of the ...
ElectronicsNoob's user avatar
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2 answers
95 views

Pull-down resistor with LED on a logic input

Imagine I have the following circuit: A register (74LS377N) has the inputs connected to a bus. In the picture, BUS0 is pulled down with a 10k resistor, so if nobody outputs to it the register will ...
Elerium115's user avatar
1 vote
1 answer
181 views

Configuring LM35 to read below 0 degrees C

I read online that the LM35 has a temperature range of -55°C to 150°C, but when testing I found that it was unable to go below 0°C. This is the code I've written to read from the temperature sensor. I ...
Shane Holmes's user avatar
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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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
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205 views

TP4056 power cutoff circuit using PFET

I want to understand this and also to make sure this will work. This is a TP4056 USB-C charging circuit. The circuit is almost the same as the regular one you'll find ordering from China. The only ...
Domenico's user avatar
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6 votes
1 answer
258 views

Active pull-down in LSTTL totem-pole output

The lower totem-pole transistor of a LSTTL IC frequently has an active pull-down from base to emitter (ground). Here is an example from TI's SN74LS93 datasheet. I was curious how this active pull ...
Math Keeps Me Busy's user avatar
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1 answer
79 views

Pulldown resistor between ICs?

I'm building a 24hr clock out of discrete logic, and I forgot to include pulldown resistors, so I'm going back and adding them. I know to put pulldown resistors on the switch inputs, but do I also ...
Nicholas Bos's user avatar
1 vote
1 answer
131 views

How is a "smart pull-down" implemented

Some devices have a smart pull-down resistor. It is active until the user drives the pin, and as soon as a threshold is reached, the pull-down is deactivated. How is this implemented, e.g. if I wanted ...
trevor's user avatar
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0 answers
128 views

Calculating the lowest value MOSFET pull-down resistor

I am using the AO3415 to do high-side switching. My aim is to reduce power consumption as this low-power device should run for ages on a single battery. System quiescent current is less than 5 μA. (...
UnknownDagger's user avatar
0 votes
3 answers
211 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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0 votes
2 answers
118 views

Why is this variable not updated during the loop?

I`m trying to obtain a PWM signal from RA4 a PWM signal when a button is pressed (button connected to RA2) using a PIC12F1572. I'm in trouble with code because run as follow: Start simulation via ...
SkePsis's user avatar
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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
2k views

"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
0 votes
1 answer
55 views

Configuring S32K148 Microcontroller 144pins LQFP pin no 113(PTA1) as pull down

I am using S32K for current measurement purpose. Using pin no 113 as ADC input. I can see in the datasheet that ,we can configure this pin as pull down or pullup. May I know is this possible to set ...
Confused's user avatar
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0 votes
1 answer
48 views

L6924U output status pins in the datasheet description are open-collector, but schematic shows a MOSFET

The battery charger L6924U has two status pins, ST1 and ST2, to tell what is happening inside the charger: charge in progress, charging done, stand-by mode, etc. In the datasheet STM always writes ...
Lyoner's user avatar
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0 votes
1 answer
95 views

MOSFET + voltage regulator usage, pull downs, common ground, schematics

As a continuation of my previous question about what type of part I'd need to control a circuit with a higher voltage, I put together schematics for what I hope would achieve what I am looking for ...
klaasbob's user avatar
1 vote
2 answers
268 views

Floating ttl input and ground short without pulldown

A pulldown resistor seems to always be used for configurations where when the switch is open the normal state is low. For example The reasons always given are to avoid a short between voltage and ...
Daniel's user avatar
  • 167
3 votes
1 answer
481 views

USB-C pulldown resistors before or after common-mode choke?

I'm designing a board with a USB-C upstream-facing port (UFP) for power only (no data). I've included a common-mode choke, as well as a ferrite bead filter in pi configuration. Since I'm presenting as ...
TypeIA's user avatar
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5 votes
1 answer
1k 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 ...
Mora's user avatar
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0 votes
1 answer
419 views

"Pull-Down Resistor" in AC circuit

Background I have an Fridland AC doorbell that I am about to make "smart". My approach is to connect a device named a shelly uni inside the doorbell that ...
Philip Johansson's user avatar
1 vote
3 answers
865 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 ...
Chris Fernandez's user avatar
3 votes
2 answers
1k 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 ...
ceremcem's user avatar
  • 1,426
0 votes
2 answers
169 views

How to calculate the pull down resistor value for an input pin in a 74HC273 flip flop?

An old circuit I'm checking was built using a philips 74HC273 (CMOS dev) datasheet in a card that is receiving reset and other signals from another card. In that other card, reset signal comes from a ...
Suvi_Eu's user avatar
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0 votes
4 answers
575 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 ...
Golamraj's user avatar
0 votes
1 answer
52 views

MCU Built-in Pull Down

I'm using a Microchip PIC24FJ1024GA606. I have two versions of my PCB and I am using a pin to identify the hardware revisions. On Version 1, the pin is unused and on version 2, the pin is connected to ...
t3ddftw's user avatar
  • 515
2 votes
1 answer
204 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 ...
Eyal Porat's user avatar
3 votes
3 answers
1k 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. ...
Neppomuk's user avatar
  • 575
0 votes
1 answer
338 views

Do I need a pull-down resistor with this MOSFET-based motor driver?

I'm using the circuit in the picture to control a 12 V DC motor with an ESP32. Do I need an extra pull-down resistor between the microcontroler pin and ground to avoid my pin floating and maybe ...
Fer P's user avatar
  • 5
8 votes
3 answers
1k 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 ...
Manu Chadha's user avatar
0 votes
2 answers
93 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 ...
Musa's user avatar
  • 298
1 vote
4 answers
394 views

Pull Down resistors value for unused pin for MCU

According to the datasheet, it is preferred to have MCU's unused pins connected to GND. That's the only thing suggested in the datasheet. I think it would not be a wise decision to directly connect ...
Z0iS's user avatar
  • 21
0 votes
1 answer
123 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 ...
Collins's user avatar
  • 21
0 votes
1 answer
124 views

Adjusting the drive strength of level-sensitive interrupt signal

In my current environment, the interrupt source comes from an FPGA on a daughter board and connects to a GPIO pin on an EVB: daughter board (interrupt output signal from SD controller)--> EVB(GPIO ...
bruin's user avatar
  • 465
1 vote
3 answers
647 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 ...
aquagremlin's user avatar

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