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Questions tagged [pullup]

A Pullup Resistor brings a line up to a voltage (Typically VCC), while allowing the line to be pulled low.

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52 views

Voltage divider with pull up resistors

I'm designing a peripheral circuit between a sensor (U1) and a MCU (U2). U1 has an open-drain output pin to indicate its status. This pin will be staying at either HIGH or LOW constantly (not ...
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1answer
70 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
37 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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1answer
47 views

Pull-up scheme for Hall effect sensors on a BLDC

I looked around on here, and used google, and couldn't find a direct answer to this question. Please forgive me if I overlooked something. I am working on a board to control a BLDC motor (BLWS231D-...
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1answer
30 views

Is the RESET signal in this LCD required pull-up resistor?

I'm designing a circuit which includes this LCD display. There is no information about an internal or external pull-up resistor for the RESET signal. the only thing that the datasheet says about the ...
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3answers
35 views

Current flow from pull-up resistor in MCU

According to the circuit diagram here, when the switch is on, the current directly flows to the ground, but shouldn’t it split at the junction and some of it go to the MCU, as well as the ground, if ...
3
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1answer
75 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
48 views

water level sensor wetting current

i would like to connect a water level sensor* to gnd+pin on an mcp23017. the pin need to be pulled-up with some resistor. the internal pullup of mcp23017 are 100k if i have read correctly the ...
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2answers
37 views

sn74lvc1t45 pullup on the DIR line

The part sn74lvc1t45 we are sing as an SPI translator. We usually use B -> A which means DIR goes to ground, however in a new design we are reversing this, and as a result, as per the DS it (being ...
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3answers
88 views

Can I use a Dupont cable with a resistor soldered in the middle as a pullup resistor for I2C comms?

The short question: is there a difference between using (on a breadboard) a standard through-hole 10K pullup resistor, versus using a modded Dupont cable with a 10K pullup resistor soldered in the ...
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2answers
35 views

Should analogue multivibrator and comparator pullup circuit have separate supplies?

I have managed to produce a design within the falstad circuit simulator for an analogue "LED chaser" using an analogue multivibrator and 3 comparators inspecting the voltage of one side of the ...
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26 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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3answers
127 views

Low power switch input with MCU wake-from-sleep interrupt?

Im trying to read the falling edge of digital logic input to wake up a microcontroller. Below is the circuit I have used. There is an RC filter to provide a ~5ms debounce time, and a 100K pullup so ...
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1answer
129 views

STM32 pulled up GPIO pins work stange after being connected to the ground

I use stm32_smart v2 development board and try make a cheap and reliable 7 bit input interface using 7 jumpers from GPIO to the ground. Internal pull up resistors are used. The first time I did not ...
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1answer
33 views

Higher Voltage = Improved Signal Strength

I'm using a reed switch to detect the state of my garage door. It's connected to an ESP8266 via twisted cables of 1.5m and each line has a pull-up as the signal floats too much otherwise. Well it ...
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0answers
61 views

Are pull-up resistors mandatory for inputs on modern parallel ports?

Here I go again testing more circuits on two computers with each reporting completely different data yet I feed the same data in. Now this time, the data coming back is all logic highs on my laptop ...
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32 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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0answers
32 views

Using internal pulldown to pull esp8266 logic pin low

I'm trying to design a linear actuator with limit switches that both deactivate the motor drive and also signal my micro-controller that the switch is active. I plan on using a DRV8871 motor ...
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2answers
152 views

GPIO push/pull and pull-up resistor?

I have a question regarding the behaviour of a MCU's GPIO pins when configured in a certain way in hardware and software. In this case I am using a dsPIC33EP, but I believe this question is generally ...
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1answer
58 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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3answers
90 views

Pull-up resistor circuit clarification

I'm new to electronics and I'm trying to understand pull-up resistors properly. I have a problem with the following schematic: I've redrawn the schematic into my following schematic for better ...
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3answers
70 views

Drive 24V input (active LOW) using 5V microcontroller

I have a device that is activated by grounding a pin that is pulled up to 24V. I want to control this using a microcontroller (ESP8266 which operates at 5V) using as little components as possible (no ...
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2answers
212 views

Measuring Rotary Encoder Signal with Multimeter

I'd like to measure the A and B signal of an encoder (https://www.amazon.co.uk/gp/product/B079H3C98M/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1) using my multimeter. I've tried testing the A ...
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1answer
110 views

MCP73833 and status to RaspberryPi

I want to use MCP73833 as a charger IC with the ability to route STAT1, STAT2, PG to RaspberryPi GPIO. Those are open-drain outputs and should be pull-up, according to datasheet. The datasheet also ...
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1answer
32 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
185 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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0answers
95 views

Minimum value I2C-pull up resistor for arduino

I'm trying to determine the minimum value of pull resistor for Arduino Uno The datasheets says; 0,4 Vol for 20 mA Iol. Let's assume VDD = 5V For formula is: Rmin=Vcc−0.4V/20mA = 4,6V / 20mA = 230 ...
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1answer
68 views

Pull-up resistor I2C value; R(min) formula approximation

For pull-up resistor of I2C, I have found formula to determine R(min). For a device with; 0,4 VOL(MAX) at 3mA IOL The calculation can be done for VDD = 5V: R(min) = (5V - 0,4) / 3mA = 1533 ohm. ...
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1answer
79 views

TCA9548A Reset Pullup Resistor

Is the pullup resistor on the reset pin of the TCA9548A multiplexer necessary if I do not intend to ever use the reset pin? The datasheet says to "Connect [RESET] to VCC... through a pull-up ...
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5answers
71 views

Indicator LED pulling up line

I have a simple circuit: (Note: RN4 is currently 180 ohms. The label got left off the image.) When the 339 is setting an output low, the output is only dropping to about 2.3v, and not 0. Not low ...
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0answers
60 views

Pullup/down works on breadboard but not on soldered pcb

I'm trying to solder a circuit done with my esp8266 on a common pcb taken on aliexpress. My pullup/down (software or not) doesn't work anymore after putting them on board. I've tested anything and I'm ...
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3answers
426 views

Can both internal and external pullup resistor be used on an MCU pin?

I am taking a microcontroller class in university and have the following problem: (Sorry for the poor image quality) Its fairly simple but here is my problem: In my solution I set the internal ...
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2answers
301 views

Removing pull-up resistors from breakout board

I use VL53L0X breakout boards for distance measurement on I2C, each with built-in level shifter and pull-up resistors (10kΩ, as measured). As I connect many of those on a single bus (5 and more), I ...
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1answer
129 views

Troublesome circuit with pull up resistors for smart power strip based on ESP8266

I'm making a WiFi power strip with a Wemos D1 mini v3 (ESP8266) microcontroller and a 4 mechanical relay board. 220v mains is converted to 5v 600mA using a HLK-PM01 which powers both the relay board ...
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1answer
99 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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2answers
1k views

Optional pull-up resistors for I²C

I need a circuit that would allow me to optionally add pull-up resistors to an I²C bus. One way would be to add two jumpers for each pull up resistor. But I thought of something like this: This way ...
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1answer
132 views

Can I pull up a 5V logic line to 12V without damaging anything? [closed]

What happens if I pull a 5V logic line (from a µC via a 74HCT245 level shifter) up to 12V with a, say, 10KΩ resistor? Is this going to damage anything? My goal is to have the logic line at the same ...
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2answers
134 views

Issues using an Ultrasonic Sensor with Raspberry Pi

I am conducting a project which needs to use a precise ultrasonic sensor but I am having trouble working it with the raspberry pi. The sensor I’m using is the Senscomp 600 series; the manual isn’t ...
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4answers
653 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
189 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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0answers
38 views

Analog to Digital convertor

I bought an analog to digital pulse module (Elster PR7) for a project for data logging of a flow meter (Elster H4000). I had following queries regarding its use and its datasheet: In the datasheet on ...
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2answers
188 views

Are internal pull-up resistors in microcontrollers connected to Vcc internally?

I'm partly on my way into my first project with the ATMega32U4 and Im trying to understand the internal pull-up resistor. After lots of research, Im struggling to find an outright answer to my ...
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1answer
852 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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2answers
592 views

How to properly pull up a single-relay module

I've previously discussed in this post how to drive the relay with an ESP8266, and eventually came up with this circuit: Problem is, the particular type of relay module used has an "active low" input: ...
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1answer
797 views

Pull up resistor on P-MOSFET gate. Not working

I am building a battery-powered datalogger that will communicate using cellular signal, based on the ATSAMD21 microcontroller and the SIM5320 cellular modem. To save power, an outside timer ...
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2answers
111 views

Pullup resistor value based on current sinking capabilities

Actually a lot simpler question than the title would suggest. I'm planning on using a SN74AHCT125 quad buffer as a logic-level converter from 3.3V to 5V. I only need two of the four inputs. As per ...
18
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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
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 ...
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1answer
104 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
237 views

How Does A Pull Up Resistor In Parallel Work?

I've been playing with a Raspberry Pi and working with simple circuits. I thought I had a decent understanding of pull up/pull down resistors, but then I purchased an Infrared Break-Beam sensor (https:...