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.

Filter by
Sorted by
Tagged with
8
votes
7answers
6k views

Does this design smell bad? Can I pull a pin simultaneously down and up?

I am building a simple circuit using PT7C4511 PLL Clock Multiplier. This chip has an OE pin that stops the output when LOW. By default (with no external signal driving it) it stays HIGH because of a ...
0
votes
6answers
113 views

Is a floating pin equivalent to a very weak pull down?

I know that if a MCU pin is configured as "input" and it is not connected to any pull up/ pull down resistor, it is said to be floating. In this situation, we could say that the pin is in series with ...
0
votes
3answers
50 views

what does pull-up resistor and pull-down resistor mean? How do I implement them in my circuit?

I am trying to understand the basics of electronics and I often come across the terms pull-up and pull-down resistors. From what I understand these resistors help the switching logic devices like ...
1
vote
0answers
43 views

Using pull-down resistor, but driving pin high by connecting to Vcc directly

I have a device that I know very little about. I have access to Vcc and Gnd pin there, and it operates on +5V. I need to drive its input pin high or low depending on a switch, that's UART RX input. ...
0
votes
3answers
93 views

Fail safe led circuit

My question is about how to turn on a led before the GPIO pin has been initiated. When the IC has just been powered on and has not yet been initiated the GPIO pins remains in state HI-Z. In Circuit-1 ...
2
votes
2answers
442 views

Purpose of a Pull-Down resistor [duplicate]

Being just a beginner I'm really getting confused of pull-down resistors. Please have a look at the diagram below. Here there is a 10k pull down resistor is connected to ground and the pin 2 of ...
13
votes
6answers
5k views

Is a pull up/down resistor really necessary?

Logical reading (1 or 0) of a micro-controller input GPIO pin may float if it is neither connected to VCC nor GND; someone said it is because of surrounding RF interference. When a floating GPIO ...
0
votes
1answer
152 views

Weird behavior on a pull-down resistor in my design

I am using a 74LS173 D Flip Flop that has some control lines that may be floating at times before they are asserted. To avoid the control line from doing something I don’t want it to do doing this ...
1
vote
2answers
64 views

Is it correct to place the base to emitter resistor in a BJT circuit as follows?

This is a follow up Question to What is use of R41 (base to emitter) resistor in Transistor Relay Circuit? My doubt is can we connect the resistor R41 between emitter of optocouler and GND? The ...
2
votes
1answer
58 views

3.3V I2C Logic on 1.8V Device

I have designed a board with the ICM-20789, but am having trouble keeping stable voltage values on the I2C bus. Datasheet I have followed the schematic that was listed inside the datasheet, and that ...
2
votes
2answers
65 views

TPS63050 Enable Pin Pull-down Resistor

I'm using the TPS63050 buck/boost converter in a design. The datasheet basically just says "don't leave it floating" in the table on page 4. I want this enable pin to be under the control of an ...
0
votes
2answers
105 views

Logic DIP switch console breadboard

I want to use a single breadboard slice to build a console for a mini-computer project. It will have 28 or more parallel control and data lines, each with the following features: state indicator LED ...
0
votes
1answer
46 views

OP-Amp 564 Output Shutdown

I need to build a controllable output shutdown for the OPA 564 so I can force the amp to shut down. The solution in the datasheet uses an optocoupler but I rather use it with some pull-down resistor. ...
1
vote
1answer
215 views

Pull down through LED

I've built my own version of 8-bit computer based on various examples in the Internet. Once built I started to face some issue with unpredictable memory changes when it was not supposed to. After I'd ...
1
vote
0answers
62 views

Using internal pullup, pulldown resistors to find floating IOs

I want to find at runtime if a GPIO is floating (nothing connected to it). I assumed I'd find tons of answers on Google, but maybe I'm searching wrong. My approach has been to: enable the internal ...
0
votes
0answers
34 views

pulled down io protection from overvoltage

I need to protect my IC's io form overvoltage(default is 5v). The pin has the capability to source 10 mA and sink 25mA I tought of using a tvs diode(between pin and gnd) and a resistor(330r from pin ...
11
votes
4answers
2k views

Is there a more efficient alternative to pull down resistors?

I am building a LED spinner circuit and I am at the point of optimizing it. The whole circuit itself only draws about 10-20mA max. I was today looking at this part of the circuit: Now as you can see, ...
1
vote
1answer
124 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 ...
0
votes
1answer
44 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 ...
0
votes
1answer
56 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 ...
6
votes
5answers
2k views

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 ...
0
votes
2answers
64 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 ...
4
votes
1answer
994 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 ...
1
vote
0answers
98 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 ...
0
votes
3answers
20 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 ...
1
vote
1answer
36 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.
0
votes
1answer
213 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 ...
0
votes
0answers
74 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 ...
1
vote
1answer
150 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 ...
-3
votes
1answer
139 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 ...
0
votes
1answer
36 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
votes
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 ...
1
vote
2answers
158 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
votes
1answer
48 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
votes
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 ...
0
votes
1answer
342 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
vote
1answer
326 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
votes
1answer
104 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
vote
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 ...
0
votes
1answer
102 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 ...
-3
votes
2answers
69 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
331 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
votes
1answer
57 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
votes
1answer
363 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
votes
0answers
69 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
votes
0answers
92 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
vote
1answer
118 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
votes
2answers
577 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
votes
2answers
487 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
150 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 ...