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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Mosfet Gate Pull-Down and Gate Resistor Failure
I'm trying to make an inverter which has a dc bus of 350V and output of 220V(spwm). The problem is I've run the circuit two times and in the first one the gate resistors explode and in the second one ...
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1answer
51 views
Pulldown for zener voltage shifter
I would like to know whether R24 has been correctly applied to pulldown the EN pin when none of the diodes are switched on.
The idea here is that voltages higher than 3.3V may be applied from any of ...
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1answer
136 views
How MCU pin reads whether it is being pulled up or pulled down?
I am a beginner in electronics. I searched on the web about Pull up and Pull down concepts. As far as I know,
1) When an MCU pin is pulled up, a small amount of current pass through the pull-up ...
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1answer
29 views
How to properly use a shut pin in audio connector to prevent floating pins when disconnected
I'd like to use this RCA jack in a project that detects roughly the volume level on an RCA audio source. The circuit filters out the DC line voltage, amplifies it with a PNP transistor and then shifts ...
6
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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 ...
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2answers
66 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 ...
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1answer
47 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 ...
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2answers
82 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 ...
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1answer
172 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 ...
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1answer
118 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. ...
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1answer
84 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 ...
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1answer
52 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 ...
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1answer
65 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
68 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
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1answer
203 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 ...
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1answer
55 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 ...
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1answer
153 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 ...
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0answers
52 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.
...
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0answers
55 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 ...
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1answer
94 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 ...
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2answers
310 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 ...
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2answers
275 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 ...
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1answer
87 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 ...
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1answer
47 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 ...
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2answers
291 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
104 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
...
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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 ...
-1
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1answer
179 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
183 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
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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: ...
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1answer
137 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 ...
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1answer
133 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 ...
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1answer
47 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 ...
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3answers
105 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 ...
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3answers
633 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 ...
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4answers
843 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
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1answer
365 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-...
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1answer
99 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....
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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. ...
20
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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 ...
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3answers
3k 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 ...
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1answer
176 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
79 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 ...
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1answer
140 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 ...
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2answers
512 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 ...
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2answers
168 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 ...
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3answers
420 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
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2answers
1k 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
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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
256 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. ...
