Questions tagged [pulldown]

A Pulldown Resistor brings a line down to a voltage (Typically Ground Potential), when no drivers are controlling the line. It prevents the line from 'floating' with an unknown voltage on it.

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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 ...
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3 votes
3 answers
577 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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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 ...
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4 votes
3 answers
123 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 ...
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2 answers
27 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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4 answers
72 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 ...
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1 answer
46 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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1 answer
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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 ...
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3 answers
113 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 ...
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1 answer
81 views

Analog sound data

I tried to make my own sound sensor on a PCB. I wanted to take analog sound data for my project. I used an ADC pin from a STM32G474, but I maded mistake while I designing. I took a KY-038 reference ...
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4 votes
1 answer
48 views

Unclocked NOR gate SR latch not latching [closed]

I am starting to learn computer architecture and decided to try building an SR latch using NOR gates and without a clock (basically copying this video) on a breadboard. My circuit is pictured, it is ...
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-1 votes
1 answer
101 views

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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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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1 answer
55 views

Pull output down if either of multiple pins are pulled down

(Sorry in case I used the wrong terminology, let me explain.) Context I have a relay board I'm controlling. It has 8 relays, and 8 low level triggering pins for control. 7 of the relays I want to ...
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3 votes
3 answers
502 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 ...
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1 vote
2 answers
98 views

Reduce current through a pull-down resistor when chip power is removed

For a battery-powered application, I'm trying to reduce the current draw of a chip when its voltage rail is removed. What is the current through the enable pin's pull-down resistor when the 5V USB-...
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0 answers
58 views

Find Vout with voltage divider + pull-down resistor

I have to calculate Vin (~5 V). After using the voltage divider formula the Vout value is pretty close to the value measured by a multimeter, but a little bit low. The question is, what is the formula ...
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2 votes
3 answers
933 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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4 answers
112 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 ...
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0 votes
2 answers
122 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 ...
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0 votes
3 answers
88 views

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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-4 votes
5 answers
428 views

Why is pull down resistor path of least resistance for the "floating" noise?

This question often pops up from people learning about pull up/pull down resistors. Why people ask it, is easy to see, it is a logical question to ask. If the pull-down resistor is bypassed at logic ...
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1 vote
1 answer
111 views

"Hardware shut off" pumps when water leak is detected

I did a lot of research but cannot find a clear solution to my problem - maybe that's also because of a lack of understanding proposed solutions, of course. After all I read, I feel confident enough ...
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1 answer
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Can pull-down resistor be connected before the gate resistor?

I noticed I have made a mistake in one of my PCBs and have connected the pull-down resistor of a MOSFET before its gate resistor (point A), rather than to the gate directly (point B, see schematic) as ...
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1 vote
2 answers
74 views

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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2 votes
1 answer
108 views

Calculation for Resistor in Phototransistor Emitter

I decided to ask here for help, I am still new at electronics, I have been trying to figure out the definitions and graphs of this phototransistor, the PT1302 (datasheet here), my doubt is how can I ...
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2 votes
1 answer
212 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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0 votes
1 answer
117 views

Saving a picture to MicroSD while streaming video upon motion detection

I am using an esp32-cam to stream video. As it is steaming I want to take a picture and save it to a micro SD card when motion is detected. Hardware: ESP8266-12e, ESP32-CAM, EKMC2604112K panasonic ...
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1 vote
0 answers
56 views

MUX Pulldown resistor Questions

I have a precision application where I am demodulating two sine waves using an analog mux (ADG613) and then Low pass filter to measure it's amplitude. The ADG613 is a 1:4 MUX made into a DPDT (chosen ...
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-1 votes
2 answers
575 views

4x4 keyboard matrix - why no pull down resistors?

I found many schematics out there for a 4x4 keyboard/switch matrix, both with and without diodes. Yet I don't get it. If one doesn't add pull-down resistors, rows 1 to 4 will all be floating. Can ...
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1 vote
1 answer
150 views

Resistor Value for controlling 5V relay

Regarding the post from: https://www.bambusekd.cz/dev/raspberry-control-5V-relay Hi I create raspberry pi project for fun and I followed this post for controlling my relay. What formula is used to ...
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-2 votes
1 answer
116 views

How to tell correctly if a circuit is pull-high type or pull-low type?

I have been giving this assignment working with Arduino that would light up a 7-segment component, when a push button is pressed. Is there an intuitive way of looking at the circuit and recognize ...
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1 vote
2 answers
961 views

Is it necessary to use a pull down resistor with this BTS7960?

I have an Arduino Nano controlling a BTS7960 that is 10 meters away. I have one 24V power supply. Both the Arduino and the BTS7960 get 5V through a an LM2596 step down converter. The BTS7960 "...
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1 vote
1 answer
96 views

Interfacing a 3.3 V pulled up output to 5 V input

I have a TIC834 stepper motor controller (https://www.pololu.com/product/3133) which works great for my stepper motor. It's however a 5 V based system. And my stepper motor includes a 3.3 V limit ...
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3 votes
3 answers
420 views

Understanding pull down resistor current flow

I'm working on an introduction to Arduino and circuits course and I've run into a stumbling block. Everything works the way the course says that it should - I just don't understand WHY it works. Here'...
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1 answer
98 views

Does this require a larger series resistor?

I am connecting a switch to an input pin on a Nexys A7-100T FPGA development board, like shown in the below image: The circuit has a 10K pull down resistor (R1 on drawing above) to ground and the ...
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0 votes
3 answers
172 views

Configuring the unused pin in CPU

I have just started designing the embedded systems. While designing the CPU and thinking from the reliability point of view I actually had few curiosities For the unused pins which are tied up to Vcc ...
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4 votes
1 answer
106 views

DAC/ADC Precision & Noise: PD Resistor/Capacitor effect

I'm developing a device that utilizes both ADC and DAC, and I have realized that my DAC output, which is fed into the op amp, is de-facto almost floating, since op amp has high input impedance. Both ...
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0 votes
1 answer
168 views

MAX3485 pull-up pull-down resistors

I want to use the following MAX3485 chip: https://datasheet.lcsc.com/szlcsc/2006181334_UMW-Youtai-Semiconductor-Co-Ltd-MAX3485ESA_C668204.pdf I do not speak any chinese, but my question is more in a ...
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0 votes
1 answer
234 views

STM32 Input Pin not working

i try to implement an input which is reacting on an high impedance 3.3V on PC14. My Configuration looks like this. ...
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0 votes
1 answer
98 views

Is there any more subtle convention for GPIO pin labelling between overlines, asterisks, and/or inverter symbols?

As a firmware developer, I've been given an old schematic that seems to have an inconsistency between pin naming conventions. Some of the signal lines from the microcontroller are labeled with an ...
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0 votes
2 answers
128 views

Am I calculating a pull-down resistor correctly?

I'm working on a board with a MAX3221. I chose this device because you can disable the DOUT-RS232 output and the RIN-RS232 input which is very important, and critical, for my application. In order to ...
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0 votes
1 answer
238 views

How to choose resistors(RD & RL) for optocoupler circuit

I am working on a project in which I am driving 6 ultrasonic sensor 4 of them are NPN (NC) and 2 of them are NPN (NO) ,for safety of the MCU I am using optocoupler EL817 for isolation between ...
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1 vote
0 answers
38 views

Single Fault Pulls up Both AND Gate Inputs

I have a situation where I have 2 inputs to an AND gate coming from 2 sensors (passing through a comparator before). If both signals exceed some predetermined value (let's say 2.5 V for sensor 1, and ...
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0 votes
1 answer
106 views

Sensor Signal Open-Circuit/Short-Circuit Faults -- Trigger Shutdown Circuit

I am working on a project where I use the signal from 2 sensors in order to determine whether I want to trigger a timer circuit that then propagates a signal to latch an LED. The sensors give voltage ...
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0 votes
2 answers
75 views

Eliminating humming from switched audio jack

I'm using a simple DPDT 3.5 audio jack to attempt to switch between two audio outputs - speakers with a built in amplifier and headphones. The speakers work just fine, but when the headphones are ...
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-1 votes
3 answers
356 views

Reading a switch without a pull-up/pull-down resistor, for input into a script

The standard way to read a switch seems to be using a pull up/down resistor. I don't have one handy (I'm doing a one-off Raspberry Pi project while travelling and don't want to buy 100 resistors) - is ...
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0 votes
1 answer
486 views

Why is my pullup resistor more noise immune than a pull down?

I have a circuit that appears to have some noise problems related to stepper motors I'm driving. When I changed some switches to use pull up instead of pull down resistors, I get better results. Why? ...
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0 votes
1 answer
815 views

Correct way to wire USB 2.0 Type C connector?

I'm playing around with building a simple keyboard, that will have just few buttons, nothing complex. I have decided to use USB 2.0 Type C connector, like this or this. Now when following USB 3.0 ...
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  • 103
0 votes
2 answers
680 views

Turn ON/OFF a LM2596 based buck converter with microcontroller

I want to turn ON and OFF a LM2596 based buck converter with a microcontroller GPIO pin. 5th pin of the LM2596 can be used to for that purpose. Please have a look on the schematic. My question is ...
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