Questions tagged [pullup]

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

Filter by
Sorted by
Tagged with
0
votes
2answers
37 views

Common resistor for pulling up unused pins of ATmega2560

I am designing a PCB with ATmega2560 MCU. I have 50 unused pins in my design. I was wondering if I can pull up these 50 pins using 5 resistors such that 10 pins have a common pull up resistor. Is that ...
3
votes
1answer
139 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 ...
0
votes
2answers
60 views

Problem with the reset circuit for a MCU

I need help by understanding the problem with an existing MCU circuit concerning the Reset PIN (STM32 Cortex M0+: STM32L071K8): It seems something in the circuit is wrong, since it works only when I ...
0
votes
3answers
16 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 ...
0
votes
1answer
58 views

Enabling/disabling a pull-up with a microcontroller (and a level shifter)

(Split up from this question) I'm trying to interface an Arduino with an eMMC chip to bit-bang it. eMMC uses bidirectional lines, and one of them (CMD) is first used in open-drain mode (for ...
0
votes
2answers
38 views

Reset switch pullup resistor placement

I noticed that pullup resistors for reset pins that are pulled to ground with a switch are commonly placed between the power rail and the pin, for example the EN pin on an ESP32. Could the resistor ...
0
votes
2answers
76 views

Why is open collector output is called high impedance and what determines the upper limit of the pull-up resistor?

Is calling open collector output as high impedance due to the value of pull up resistor or due to the fact that the IC itself do not source any current? And what determines the upper limit value of ...
1
vote
1answer
42 views

Pullup resistor operation between the ESP32 and a Bus MCU

I have an ESP32 as my main controller and a Bus. The bus operates where Pins 55 & 56 needs to be HIGH in order for the bus to be OFF. My ESP will drive the bus by enabling it by pulling those ...
0
votes
2answers
105 views

How to connect multiple devices to UART bus? [closed]

I want to use a UART bus (RX-TX-GND) to communicate between one master and multiple slaves. NUCLEO-F401RE board is the bus master. B-L072Z-LRWAN1 and ESP32 are the slaves. Communication over UART ...
0
votes
2answers
50 views

Sensor 3.3 V to 5 V pull up schematic

I am designing a circuit for a PCB that will incorporate an ultra-sound sensor (HCSR04.) The sensor needs 5V for supply and its input pin also requires 5 V. The MCU that I am using has pins that ...
2
votes
1answer
70 views

Some LTspice questions. Decoupling capacitor doesn't effectively block DC. Pull up resistor voltage doesn't drop to logic low level

I'm trying to design an interfacing board that is used between a micro-controller and a phone simulator (a picture of the schematics is attached). The 44VDC is used for the phone simulator to detect ...
0
votes
1answer
33 views

Is Pull-up present by default?

I'm using the MC9S12DP512, Motorola's microcontroller. I was executing a service and ,at the end, I put low logic level at the pins PS4, PS5 and PS6, then after that, I configured these pins as inputs....
1
vote
1answer
51 views

IR2110 - Open Collector Output Problem

I'm trying to design an inverter and I'm using 2 IR2110 as gate drivers but my MCU board PWM outputs are open collector, I've added a pull-up and transistor to feed IR2110 with 5V pulses but it's not ...
0
votes
1answer
71 views

Disadvantage of using low resistor value for pull up (Strong pull up)

I was trying to choose a resistor value for a pull-up resistor I will use in my project. The project will have I2C communication and SMBus communication. When I was searching on the internet, I have ...
-3
votes
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 ...
1
vote
2answers
113 views

SMBus pull-up resistor value

Hello I need to communicate with a device using SMBus. However, I could not choose correct value for pull up resistors. Vdd is 4.9V and I use SMBus. In same conditions for I2C communications I used 2k ...
0
votes
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 ...
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 ...
0
votes
3answers
141 views

doubt when Arduino connects to multiple i2c devices

I am using Arduino nano to drive multiple i2c devices, actually, they are premade modules which are available on eBay. ads1115 ADC, ds3231 RTC, 20x4 character LCD i2c module, at24c02 EEPROM module ...
1
vote
2answers
83 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 ...
1
vote
2answers
145 views

UART/I2C Pull up resistors

I have question regarding the pull-up resistors when UART/I2C lines are running on 2.5V and GND. Is it OK if pull up resistors are used on these lines which are connected to 3.3V or Vice versa when ...
0
votes
0answers
37 views

Pull up high voltage

High voltage switching using N-FET This is my former question. The question comes down to, how should I build a pull up for a 50V operated system using 3.3V singal. The voltage I have available is ...
0
votes
1answer
75 views

Prevent design to power up when updating firmware in flash memory

I have an FPGA based design using the MachXO2 by Lattice. I wanted a quick, easy and clean way to perform firmware updates, which are frequent, so I decided to use an external flash memory (AT25SF041 ...
0
votes
2answers
41 views

Pcf8574ap to to manage the 4 address pins of 4067 multiplexer?

I have a question. I have a 4067 multiplexer connected to my Raspberry Pi, 4 GPIOs turned on or off, control the channel of the multiplexer. My problem is that if no channel is changed, my code is ...
0
votes
0answers
44 views

Opto-coupler and switching digital pins

I'm a total noob when it comes to the use of opto-couplers, but I'm trying to connect up a couple of digital pins between an ESP32 and a small voice module. There are two pins that I need to switch ...
0
votes
1answer
79 views

Tactile touch button design using pull up resistor

As you can see on my github https://github.com/mancio/Volante-The-Gamepad I'm designing a gamepad with analog axes and digital touch buttons using pull-up resistors My pull-up resistor switch works ...
2
votes
2answers
86 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
60 views

I2C pullups for level shifting

If I want a breakout with two sensors on it, one operating at my MCU's voltage (3.3V) and the other requires a drop to 1.8V, do I need two sets of pullup resistors for both voltage lines? Can I do ...
1
vote
1answer
284 views

MDIO bus pull-ups

What is the proper way to connect multiple ethernet devices via MDIO bus? I know that MDIO (similarly to I2C) is open drain, so I think that I need (just as in I2C) two 1-4, 7 kOhm pull-ups both for ...
1
vote
2answers
95 views

Pull up to 5V on a wire that may occasionally see 60V

I have a wire that either floats - that's when I want to pull it up to 5V - or it may see up/down to +/-60V applied to it - and that's when I really don't want it to be connected to the 5V rail. ...
0
votes
1answer
215 views

I2C driver for MSP432

I am trying to develop a I2C driver for MSP432. As of now, I am interfacing a accelerometer through USCI B2_ module on MSP432. The problem that I am facing is I am getting a NACK in the IFG register ...
1
vote
2answers
234 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 ...
0
votes
1answer
89 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 ...
0
votes
1answer
71 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 ...
0
votes
1answer
173 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-...
0
votes
1answer
37 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 ...
0
votes
3answers
94 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
votes
1answer
236 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
62 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 ...
0
votes
2answers
52 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 ...
1
vote
3answers
174 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 ...
0
votes
2answers
38 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 ...
0
votes
0answers
56 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
3answers
279 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 ...
1
vote
1answer
356 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 ...
0
votes
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 ...
0
votes
0answers
131 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 ...
0
votes
0answers
65 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 ...
0
votes
0answers
61 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 ...
1
vote
2answers
409 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 ...