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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42 views

Modification to Arduino 12V Detection Circuit

I'm upgrading the interior lights on an older model vehicle. The plan is to tap into the very simple lighting circuit (always hot with a switch for on-off-door) to detect each scenario. Light switch ...
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1answer
32 views

Unused pins on H6 Allwinner SoC

I am looking at a reference design for the allwinner H6 SoC. My question is pretty straightforward. Why does pin B3 need to be powered if the EPHY pins are unused. Additionally, pin B4 is being pulled ...
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51 views

LEDs flicker when I move my circuit

I'm building an LED driver circuit, CD4504B and TLC5916 controlled by a Raspberry Pi: simulate this circuit – Schematic created using CircuitLab I'm finding that sometimes when I move the ...
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Should I use a resistor between the gate driver and MOSFET (gate pin)?

I'm making a PWM driver for a DC motor. After some questions were answered in this post, I ended up with this schematic: And I have some new questions: Do I need a resistor between the gate and the ...
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2answers
48 views

Inverted high impedance / pull down circuit

I'm devising a circuit to control the shutdown input on an integrated circuit. The IC accepts a high impedance input (can't be pulled to any voltage) to enable operation, or it can be pulled down to ...
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1answer
216 views

Why would a USB-C adapter have a pull-up resistor?

I'm talking about a USB type-C male to USB type-A female adapter, the ones you need to connect a USB flash drive to the latest MacBooks. According to USB-C specification, this sort of adapter needs a ...
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0answers
67 views

Switching between outputs using irfz44n mosfet

In the circuit shown, the input voltage to the op-amp ua741 is 1V and the output will be 5.7V, which switches the bottom left irfz44n mosfet on and the off voltage irfz44n mosfet off. So i would ...
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3answers
18 views

On SN65HVD1780 are external pullup and pulldowns

On transceiver SN65HVD1780 are external pullup and pulldowns required on A,B,DE,RE,D,R lines? The datasheet mentions that the part has internal pullups and pulldowns but it's not clear if external ...
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1answer
32 views

Pull down for 74HCTXX series logic ICs

I am building an adder with standard 74HC/HCT series logic ICs. I see the result when input pins are left floating are erroneous. Shall I have to connect some pull down resistors. Thank you.
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93 views

Pull down resistor with 24v

What is a good value for a pull-down resistor, which when switched, connects to 24v? Is there a formula to derive this? This is effectively how it's drawn in the schematic (the inverter input's ...
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0answers
58 views

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
105 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
137 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
30 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 ...
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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
91 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
87 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
248 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
198 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
96 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
57 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
79 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 ...
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1answer
269 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
256 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
61 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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75 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
109 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
469 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
351 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
118 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
55 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
342 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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129 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 ...
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1answer
217 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
219 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 ...
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4answers
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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
174 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
152 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
50 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
130 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
772 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
941 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 ...
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1answer
507 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
118 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
2k 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
5k 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 ...