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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1answer
35 views

Can i tie the enable pins directly to the rails?

i am having trouble with the spaces on my circuit and removing the two pull-up/down resistor on the enable pins would solve my problem ( if of course it doesnt cause other problems). I was wondering ...
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1answer
72 views

Can I share a single pull resistor on multiple enable pins to save space?

I am using this Schmidt trigger IC SN74HCS125 which has 4 channels I would like to save some board space by hopefully using only one resistor to pull down the enable pins of each channel. I do not ...
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Choosing the proper value for a pulldown resistor in a logic circuit

I am designing a logic circuit where the inputs are some switches and also some digital inputs are needed, below is an example of the circuit used to enhance the switches as digital inputs. I am ...
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3answers
69 views

How does a pull-down prevent a “false 1” in a pin?

yesterday I asked a question about pull-ups and pull-downs and resistance in an input pin, but I feel that the question that invaded me today is different from my yesterday's post so this is why I'm ...
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4answers
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Do microcontrollers have a big resistance?

Well, it maybe seems a very basic question, but I have this question because I'm trying to understand the 0 weak and 1 weak on pull-ups and pull-dows, for example: Here, when the button is not ...
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3answers
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Microcontroller Unused pins Configuration

I am having this microcontroller - S32K142 64 pin 5V core voltage I have a few pins which I don't want to use. While checking the datasheet of the Microcontroller, I couldn't find any information ...
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3answers
75 views

do we only use pull-up resistor or pull-down resistors when dealing with switches?

I have heard people state that if your micro controller is not reading the signal properly, then we need to use a pull-up resistor. Which I don't get? It makes sense when switch is involved because ...
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0answers
75 views

How can I use pull up and pull down resistors in an H-bridge?

I have to build an H bridge out of the following components 2 PNP transistors 2 NPN transistors battery 9V 4 resistors for the transistors a DC motor I connected the above equipment but, I also ...
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3answers
64 views

Choosing Resistor Values

I am going through analog electronics. I have seen many designs but I have a few questions below : My Questions : I understand that resistors are used to limit current in some places. And in other ...
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1answer
51 views

How to know the maximum pull up/down resistor of a specific logic pin of an IC?

I am designing a circuit and needs to place some pull downs on the address pins of PCA9546 and usually my go to resistor values for these kind of situations is either 10k ohms or 100k ohms. These ...
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3answers
56 views

Pull-up/ pull-down resistors in CMOS gates

Can someone help me with understanding why the next two circuits have those outputs? My initial schematic contains only one inverter, and the signal is 5V for output high state, and 0V for low. Now, ...
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3answers
498 views

MCU with ultra low energy gpio input [duplicate]

I am working on a project with an energy friendly MCU from Silicon Labs. The EFR32BG1B132F256GM32 to be exact. My goal is to use as little power as possible to maximize the lifespan of the CR2032 ...
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223 views

RS485 Pull-up, Pull-down and single termination resistor

Currently I use for Modbus RTU via RS485 with a shielded cable length of about 5 meters and a bitrate of 19.200 bit/s. Wired are 680 Ohm pull-up (A->+5V) and pull-down (B->GND) resistors near to the ...
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1answer
55 views

Pullup resistors value of STM32F103C8T6 GPIOs too weak, why not more flexible?

I'm trying to get a keypad to work, writing my own library (just because I want to learn it, and later use the keypad). For the columns I need pullup resistors, and I initially selected the internal ...
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7answers
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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 ...
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6answers
128 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 ...
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3answers
69 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 ...
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0answers
44 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. I ...
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3answers
100 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 ...
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2answers
518 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 ...
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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 ...
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1answer
176 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 ...
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2answers
81 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 ...
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1answer
165 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 ...
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2answers
93 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 ...
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2answers
167 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 ...
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1answer
56 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. ...
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1answer
224 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 ...
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0answers
66 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 ...
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0answers
41 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 ...
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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, ...
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1answer
246 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
57 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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1answer
63 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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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 ...
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2answers
82 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
3k 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
134 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
21 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
39 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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1answer
403 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
98 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
213 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
140 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
54 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
274 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
52 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
93 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
452 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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