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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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5answers
2k views

Reasons for having MCU pin-states default to pull-up/down out of reset

On many MCUs, pin-states default to tri-stated (a.k.a. analog inputs) when the MCU resets so as to not affect the circuits they are connected to until software configures the pins. The tri-stated ...
0
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2answers
56 views

Where to connect unused 555 timer ICs pins?

simulate this circuit – Schematic created using CircuitLab This question might not have a close answer since I think it heavily depends on the considered pin and IC. However, consider, for the ...
0
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1answer
46 views

Circuit MOSFET Pulldown Circuitry

Now, I have already made some progress, I have figured out what the W/L should be and made most of the circuit. Though I am not sure how I should put the MOSFETs ...
2
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2answers
79 views

Unusual behavior when controlling a Button Matrix

I have a 4x4 matrix for 16 buttons. Each row/column is directly connected to the pins of an unknown microcontroller. When I connect the pins directly to each other, the microcontroller behaves ...
0
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1answer
119 views

5V to 3.3V for bluetooth module - Is a voltage divider ok?

So I purchased the JDY-10 BLE 4.0 module and a very small MCU which only is capable of feeding 5v. Since I'm not an electrical engineer, I've been reading a bit on the internet, and so far, I ...
1
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1answer
89 views

Noninverting optocoupler with a pulldown resistor

I am using a power MOSFET to switch a solenoid valve. The MOSFET is driven with a optocoupler (LTV-847) to isolate the 12V required to switch the valve from the 3.3V used by the microcontroller. ...
0
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1answer
81 views

I2C Pulldown Resistor

Usually pullup resistors are needed for i2c but if I have pullups in master and hosts devices and when I add another one device to I2C bus then bus stop working. I cann't remove pullups. Does it make ...
1
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1answer
50 views

What to do with internally unused pins on a non-programmable device?

I'm designing a board for using the FLIR Lepton 2.0 LWIF camera (datasheet at https://www.flir.com/globalassets/imported-assets/document/lepton-engineering-datasheet---without-radiometry.pdf), and ...
0
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1answer
57 views

Debouncing IC input resistor?

I've recently been working on a breadboard compatible compact debouncing PCB. I found the MAX6816, a debouncing IC - check the spreadsheet here. I made the below simple circuit as per the "Typical ...
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2answers
67 views

My pulldown resistors don't work when connected to my battery pack

As I'm relatively new to Arduino and electronics, in general, I'm having some issues. I have a project that uses 6 analog pins. However, when testing the pins I would get random voltages. I researched ...
3
votes
1answer
163 views

How to “Pull Down” LVDS input in FPGA

One of my hardware modules uses a state machine which is triggered when the input signal IN is HI (that's an LVDS pair on Microsemi proASIC FPGA). The problem arises when nothing is connected to the ...
0
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1answer
54 views

Base resistor configurations, are there any differences?

Sorry for the noob question. From my understanding, R1s acts as pull down resistors for the base and R2 will limit the current flow to the base. I have seen both configurations, but couldn't work out ...
0
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1answer
123 views

Problems with input leakage current in a microcontroller

I'm trying to build a system in which a microcontroller receives (through one of its input pins) a logic 1 if a switch is pressed and a logic 0 if it's not. For that purpose, I want to implement a ...
0
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0answers
47 views

Behavior of an ECU Digital Output (0-24V) to another ECU (pull-up i guess) input

Recently i had to control a functionality of an ECU using a separate system (another ECU). ECU "A" provides an input pin which if measured in open circuit shows 12V, so i guess it is a pull-up input. ...
0
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0answers
47 views

How to switch off from headphone jack insertion

I am trying to control a boost converter - I want it on when headphone jack inserted and off otherwise. It is on when it's EN pin is >1V and off when EN pin<0.2V. I would also like to be able to ...
1
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1answer
85 views

Pull up/down a pin on a PCA9536 does not register?

Quite a obscure question here, concerning a very specific I2C expander IC, however I believe that this example can be replicated with most expander bus ICs. I am using a PCA9536 to switch the 4 pins ...
0
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2answers
215 views

Do you need a Pull down resistor when the line has an LED connected?

basically, since the LED is a diode that is tied to GND via a Resitor, does that mean it can double as Pull-down resitor for that line? simulate this circuit – Schematic created using ...
0
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2answers
223 views

Pulldown to prevent floating input pins for multiplexer

I'm designing a multiplexer shield for Arduino, by which it will (hopefully be possible to read up to 64 analog inputs such as potentiometers etc.. Schematics of rev.0.1 can be found here. I'm using ...
2
votes
1answer
77 views

Why does a Pull down resistor not affect AC

I've been reading up and trying to learn about Guitar Pedal circuits. I have a very basic question about how a Pull Down resistor is used at the beginning and end of a circuit to avoid a popping ...
0
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1answer
42 views

Pulling voltage on a “pull-up” input down to match voltage of voltage output from another device

I have a large lithium (LiFePO4) battery pack composed of 16 cells in series. It is monitored by a BMS (Battery Management System) which is interfaced to a battery charger (Victron Quattro). The BMS ...
0
votes
2answers
259 views

pull up or pull down resistor for optocoupler

I tried to make a PWM AC dimmer circuit which found in instructables.com as below: but the 100k 1W resistor got hot. Could using a pull up (or maybe pull down) resistor for optocoupler solve the ...
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2answers
94 views

Read state from LED in another circuit

For a current project, I have to read the state of an LED in another circuit with a Raspberry Pi. My current schematic is this: simulate this circuit – Schematic created using CircuitLab ...
0
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1answer
26 views

Replace Switch to power AV Receiver

How to close a circuit using a 5V power signal? Essentially the goal is turn on an AV receiver, using the internal power ON/OFF switch, to activate using a 5V control signal. The receiver now uses a ...
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1answer
164 views

What is the functionality of the pull down resistor in mosfet circuits? [closed]

I would be appreciative if the functionality of the pull-down resistor connected to the output of a mosfet circuit could be explained thoroughly. Is it mandatory to have the resistor and also the ...
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3answers
170 views

Are Pull Down Resistors too Slow to read Encoder Counts? [closed]

I'm planning on using the LPC1768's QEI module for reading a motor's encoder (which has a high resolution - http://encoder.com/literature/datasheet-770.pdf). I've read some people have hooked up ...
10
votes
4answers
4k views

What is the purpose of the 10kΩ resistor in this circuit? [duplicate]

Below is a simple circuit involving an Arduino, a push-button, and an LED. However, I don't quite understand what the purpose of the resistor is. Wouldn't the circuit function without it? Note: ...
0
votes
1answer
123 views

Using a transistor to control a pull-down switch

simulate this circuit – Schematic created using CircuitLab I have a Runcam 2 video camera. It uses a temporary switch to turn on/off and start/stop recording. I would like to control these ...
0
votes
1answer
123 views

Arduino Nano pins are always high

i started to build an infrared transmitter (commander). I use 4 pushbuttons for left, right, up, down. These buttons are pulling down when pressed. I used internal pullup resistors. My prboblem is ...
0
votes
1answer
46 views

Protecting reset pin from overvoltage

I'm designing a board with a control port. The control port allows an external controller to reboot the system by pulling the BRD_RESET low, effectively restarting ...
0
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3answers
93 views

Choosing pulldown resistor for 74LS86

I am trying to build a half adder using a 74LS86 XOR gate. Initially I connected both input pins that I am using (9 & 10) on the 74LS86 to the ground rail using 10K ohm resistors. I then connected ...
0
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3answers
545 views

Pull-down resistor confusion

I can't seem to find decent information on this topic as all articles only explain general concepts of pull-ups and pull-downs or only cover pull-ups in greater depth. I understand the general ...
3
votes
4answers
785 views

Pull-up or pull-down when building an LED ROM for 74HC logic levels?

I want to build a LED ROM (a diode-ROM, but using LEDs). The LEDs will be driven from the outputs of a 74HC138 or similar. They will drop 1.6 - 1.7 V (red). The ROM will have eight words of ...
2
votes
1answer
311 views

DDR4 pull-up resistors and decoupling clock lines

I am trying to understand the layout of a DDR4 chip connected to a FPGA. The schematic follows: I tried to look for datasheets from the memory manufacturer explaining how to properly pull-up or pull-...
0
votes
1answer
74 views

Pull down resistor and voltage on DO

I am currently having an issue with DO's on an Arduino in a constant state of high with a pull down resistor attached to a ground plane. Voltage being measured on the DO is 3v. Pull down resistor is 2....
0
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1answer
1k views

BOOT0 circuit design in STM32f446

I'm designing STM32f446 chip in PCB in a project. It will be programmed through SWD. but I'm stuck with (BOOT0) pin. I want it to be (0) as recommended. The thing is that there is no enough info. ...
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7answers
4k views

Why I2C designed to work with pull-up resistors and not pull-down ones?

I understand that in I2C, SCL and SDA lines use pull-up resistors and the pin drivers are open collector NPN devices which can drive pins to ground. This gives I2C an advantage that the same bus now ...
15
votes
3answers
2k views

Why do we need external pulling resistors when microcontrollers have internal pulling resistors?

Microcontrollers do have internal pull up-pull down resistors yet most of the circuits have external pulling resistors. I looked on Google for answers and a few sites said that those resistors are ...
0
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1answer
152 views

Pull-Down / Pull-Up Resistor value for minimum current leakage

I'm using a step-up converter (MT3608) to convert 3.3V to 5V Output. However, because I don't need the 5V all the time and my device is battery powered, I want to turn off the MT3608 IC through its EN ...
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2answers
77 views

Why we don't use pull down resistors for implementing I2C protocol ? And why resistance value varies in I2C depending on its speed?

I have read that we have to pull-up the SDA and SCK lines because the lines are open drain/open collector. But I don't understand why can't we use pull-down? Secondly why the value of resistance ...
1
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1answer
130 views

Does this schematic represent the fritzing circuit properly and can you explain how pulled low works in this IR sensor?

I'm attempting to represent the following fritzing diagram* as a schematic (using circuitlab). *from https://learn.adafruit.com/ir-sensor/testing-an-ir-sensor Here's my representation of the circuit ...
0
votes
2answers
458 views

Given a pull-up network, draw the complimentary pull-down network (CMOS gates)

this is for my computer organization class (I am a CS major), but I figured this post belongs better here than on stackoverflow. I am asked to draw out the complimentary pull down network for the ...
0
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2answers
150 views

When to use pull up/down resistors on IC inputs

In a very general sense: When should you use pull up or down resistors on IC inputs and when should you connect the pin directly to Vcc/GND? Particularly if no impedance is mentioned for the pin. Or ...
0
votes
3answers
372 views

Pull-up vs Pull-down for contact switch?

I am designing a simple contact switch(tactile, which conducts when you pushes, and springs back to not-conducting when released) interface with a microcontroller. It's GPIO has option for both ...
7
votes
2answers
898 views

Why does 10k ohm pull down resistor not work for pushbutton with NOT logic gate?

I made the following circuit on a breadboard using a 10k resistor, 100 ohm resistor, LED, and 74LS04 NOT gate. I expected this to work since the input of the NOT gate is at 0 volts when the switch ...
6
votes
7answers
2k views

Getting two (or, one and a half) outputs from a single pin

I am doing a project with an ATtiny85 and of course I'm short on I/O pins. One idea I had was to use a single pin for two outputs (let's call them EN and DATA). simulate this circuit – ...
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2answers
236 views

Pull down resistor value in debouncer circuit

I am from computer background and have made debouncer circuit (SR) using NOR gate IC HD74LS02P as a part of digital electronics project. I have used pull down resistor at all inputs of the gates used. ...
0
votes
1answer
34 views

How to decide pulling low on an IC?

I am using MAX1484 chip for communicating thru RS485. It is a two way communications with Receiver and Driver built in. If I am to use only the receiver part and I want to disable the driver part, I ...
0
votes
2answers
133 views

MSP430G2553 and LDO ADP162: Is an external pull-down necessary?

I need to control the 'IN' (enable) pin of this LDO Voltage regulator (ADP162) with a microcontroller (MSP430G2553). In the datasheet of the LDO, I couldn't find whether or not it has an internal pull-...
0
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2answers
346 views

I2C - Certain Slaves not Pulling the Lines down fully

I have a large number of boards deployed with a TI CC3200 microcontroller and a variety of sensors for an industrial monitoring application. I have been having an issue for some time now, on some of ...
0
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1answer
125 views

Difference between pull up, pull down input high and low current

I want to ask about the difference between the following when I was reading through a datasheet: ...