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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69 views

Is there any more subtle convention for GPIO pin labelling between overlines, asterisks, and/or inverter symbols?

As a firmware developer, I've been given an old schematic that seems to have an inconsistency between pin naming conventions. Some of the signal lines from the microcontroller are labeled with an ...
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111 views

Connecting both ends of battery with a resistor is fine?

I recently just started learning about electronics and electricity. After a lot of reading this is my current understanding about a battery. If you buy a battery it is labeled + or - on each end. The +...
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35 views

What does “Default Output State” mean for a digital isolator?

I do not understand the term "Default Output State" of the SI8422AB-D-IS digital isolator. I saw it on this datasheet at page 3: Does it mean "the default output voltage if the input ...
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53 views

How to choose resistors(RD & RL) for optocoupler circuit

I am working on a project in which I am driving 6 ultrasonic sensor 4 of them are NPN (NC) and 2 of them are NPN (NO) ,for safety of the MCU I am using optocoupler EL817 for isolation between ...
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Why do some PCB designers put pull-up resistors on pins where there is already an internal pull-up?

I'm going to use a DP83848I Ethernet PHY chip and I have noticed that a lot of people put pull-up resistors on these pins: LED_CFG PWR_DOWN MDC RESET_N Example: Why? According to the datasheet, ...
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93 views

What are these pull-ups for on BLDC driver reference schematic?

I'm trying to design a simple BLDC motor controller using L6234 driver IC. Looking at its application reference schematic I came across some weird pull-ups (highlighted in green, I assume these ...
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1answer
33 views

Single Fault Pulls up Both AND Gate Inputs

I have a situation where I have 2 inputs to an AND gate coming from 2 sensors (passing through a comparator before). If both signals exceed some predetermined value (let's say 2.5 V for sensor 1, and ...
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1answer
30 views

Sensor Signal Open-Circuit/Short-Circuit Faults — Trigger Shutdown Circuit

I am working on a project where I use the signal from 2 sensors in order to determine whether I want to trigger a timer circuit that then propagates a signal to latch an LED. The sensors give voltage ...
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1answer
48 views

MicroSD with STM32 and SPI mode - pull-ups and EMI filters

In the context of using the STM32F103C8T6 microcontroller I wonder I am thinking about the most practical and relevant method of the microsd application in the device from the point of device security....
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69 views

I2C pull up arduino mega 2560 issue

We're communicating Arduino Mega 2560 I2C with MCP4728 and INA219 MCP4728 address are 0x60, 0x61, 0x62 and INA219 address are 0x40. With 10k resistor as pull-up we're getting signals as below for SCL ...
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52 views

How to provide 3 options (pull-up, pull down and Open) in an IC

I have MAX9278 Deserializer IC. I have 2 doubts. Doubts : I am performing the schematic now. Below, I need to provide options for both 24-bit, 27-bit and 32-bit. How to provide the provision for all ...
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Reading a switch without a pull-up/pull-down resistor, for input into a script

The standard way to read a switch seems to be using a pull up/down resistor. I don't have one handy (I'm doing a one-off Raspberry Pi project while travelling and don't want to buy 100 resistors) - is ...
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Water well water level sensor (indicator)

I have a 400ft well, and I want to have a buzzer comes on every time water drops below certain level(280ft). At the moment, I got it working using a 12V battery and a multi-meter. I dropped down an ...
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1answer
135 views

Why is my pullup resistor more noise immune than a pull down?

I have a circuit that appears to have some noise problems related to stepper motors I'm driving. When I changed some switches to use pull up instead of pull down resistors, I get better results. Why? ...
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Why is the sensor value at the optocoupler wrong?

I am using six inductive sensors in my circuit. Four of them are working fine, but two sensors are showing very weird behaviour. I am using an optocoupler to read their output to the MCU for isolation:...
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1answer
64 views

Correct way to wire USB 2.0 Type C connector?

I'm playing around with building a simple keyboard, that will have just few buttons, nothing complex. I have decided to use USB 2.0 Type C connector, like this or this. Now when following USB 3.0 ...
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1answer
309 views

What pull-up or pull-down resistors to use in CMOS logic circuits

I use a lot of "wired or" circuits where rather than using a logic gate in an IC package I simply use diodes (eg. 1n4148) into a destination gate that has a pull-up or pull-down resistor on ...
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1answer
156 views

Will this ADC be able to drive the GPIO inputs of my Jetson Nano?

The Jetson nano Dev Board uses a voltage level translator on the GPIO (TXB0108) to convert from 3v3 to 1v8. (As given in the reference document.) I would like to drive this ADC, the AD7091R-4, to ...
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37 views

NRST Pin pull-up resistor on STM32F303RET6

The datasheet from the STM32F303RET6 shows that a pull-up resistor (a weak one?) is already included in the device itself. Rpu. But my knowledge tells me I have to add one myself in front of NRST, ...
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3answers
94 views

Why doesn't my pull-up work on S-35770 I2C counter IC?

I designed the following PCB from the schematic below to make a breakout for an I2C counter IC, datasheet is here. However my RST pin doesn't go up and the IC stays in reset state. I'm feeding 3.3V to ...
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21 views

THVD1550 Transceiver

I got this IC in my circuit and I'm wondering if I could hook up a pull-up network to it, in the following way: Since it's an RS485 transceiver, the input to it is differential. I need to know if I ...
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1answer
785 views

The idea behind using a pull-up resistor

I want to understand the idea behind using a pull-up resistor. While looking on the Internet, I came across the following description: By using these two pull-up resistors, one for each input, when ...
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Art of Electronics, Second edition pp. 73-75 — question about pull-up resistor and the logic of current setting

Edit: As you can see in the comments, I got a great explanation about the pull-up resistor question. I also wanted to make more of a bullet point of the PNP question as follows: When it comes to ...
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453 views

STM32 HAL_GPIO_WritePin not working

I am using an NUCLEO-F411RE and try to use the GPIO with HAL. Its the first time i am facing this problem. I initialized the GPIO Pins like this: ...
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1answer
68 views

What is the point of R3 in this reference design?

The TPS565201 datasheet (page 5) specifies that EN has a typical resistance of 245k to GND so I know it is safe to connect EN directly to 12V (max 19V rated). My questions is if there is already an ...
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1answer
87 views

Pull-up resistor

I am making a BLDC motor controller , so can you tell me the use of pullup resistor connected in the feedback of hall sensor.And is HO is equal to VB voltage when driver circuit operates ? Please ...
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45 views

Total length of cable to connect 1-wire DS18B20 sensors without problem

Based on this topic and the connection that is proposed I would like to make two questions (if somebody has face the same problem/task). So can I connect the data cable to a raspberry GPIO and then ...
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1answer
258 views

Understand an I2C clock line implementation

I am trying to understand a C function from a legacy project which is supposed to manage the clock line for an I2C interface. It basically does as follow: Set pin to output: ...
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119 views

How can a ESP8266 GPIO pin voltage be higher than source voltage?

I have a project that uses an esp8266 12F module and have recently had 2 boards fail on the same pin. It is GPIO12 and is being used as an input with the internal pull-up enabled. The pin is connected ...
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1answer
46 views

Is it generally OK to ignore the current in and out of a MCU pin when analyzing circuit external to the MCU?

From here, I see below illustration about the pull-up resistor. And the article says: With a pull-up resistor, the input pin will read a high state when the button is not pressed. In other words, a ...
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1answer
49 views

Does the 74LS09 have an adequate internal input pullup?

I want to feed an output of the 74LS05 open collector inverter into one of the inputs of the 74LS09 AND gate. The internal schematics in the datasheet shows that there is an internal resistor and 2 ...
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1answer
57 views

Voltage is 0.05 when switch is closed

I am new to electronics. Iam designing a simple circuit where I have to make a digital switch: Here is what I have designed in Proteus: There are 2 issues: I want it to output 5V when I close the ...
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1answer
38 views

what will happen when providing two pull up resistors in same line

If two pull ups given in a situation one pull is 4.7 K-ohm and other pull up is 10 k-ohm was given to open-drain pin then what will happen? Imagine the open-drain was connecting to an IO pin of an ...
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37 views

Understanding Master/Slave trigger configuration through open-drain GPIO

I am working with two industrial cameras that I want to trigger synchroniously through hardware triggering. For this the STROBE_OUT pin (which is an open drain pin) from one camera (Master camera) ...
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52 views

Button is giving me the same voltage when pressed or released

I am doing a simple program with my PIC (PIC24FJ1024GB610). When a button is pressed the LED is turned on, when it is released LED is turned off. I presumed that the input pins have a pullup resistor ...
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2answers
627 views

Pullup resistors. Does it make any difference what side of the series resistor?

The line is high frequency digital line. It has to be pulled up. Does the side of the series resistor make any difference? simulate this circuit – Schematic created using CircuitLab or ...
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98 views

Why does the length of the wire matter to the value of the pull up resistors?

In this DHT-11 datasheet the following sentence was mentioned (on page 4) A typical application circuit recommended cable length shorter than 20 meters with a 5.1K pull-up resistor when greater than ...
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1answer
122 views

Pull-up and pull-down resistors for RS-485 TTL I/O pins

I'm Using a THVD1451 for full-duplex RS-485 communication. In Datasheet, for transient protection against surge transients, it's recommended to use the circuit below: In this circuit, there is a pull-...
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1answer
98 views

ESP32 using Arduino: Internal Pull-ups don't work on GPIO25 or GPIO32

I'm programming a custom ESP32 board using Arduino where GPIO25 and GPIO32 are connected to pogo pins via short 5mm traces and to nothing else. The goal is to poll for a short between them as part of ...
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96 views

Wired AND, OR gates and compatibility with TTL/CMOS fan-out?

When the AND gates run out, and I just need one more, I like to use a "wired" gate, simple resistor-diode logic. Here is AND and here is OR Now for the pull-up resistors, I use just 1 kΩ ...
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1answer
66 views

I2C issue with 3.3V MCU master and 5V powered IC slave

I am trying to describe the issue I have as clear as possible here: I have two self built development boards around a Silicon Labs EFR32 MCU. The boards are identical, but I encounter two different ...
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Bluetooth Module Normal and Standby Mode configuration

I am using a BT module that can be pulled high for normal mode and pulled low for standby mode. The I/O pin 26 is connected to the MCU GPIO. Theory of Operation: When BT_WKUP = 0 --> BT module goes ...
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0answers
46 views

External vs internal pull-up resistor

I'm using an esp8266 to read signals from a water meter. The meter periodically closes a switch between two wires. My prototype circuit works fine with either an external pull-up resistor, or using ...
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1answer
85 views

False button read problem

I have a main PCB and 3 button boards. You can see the connection at bottom from my ugly paint sketch. Each button board has 2 push buttons and a power LED. One of the buttons is switching GND and ...
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1answer
55 views

MCP23017 IO expander not properly pulling up signal

I'm writing firmware on a particle argon board that needs to use the MCP23017 IO expander to detect if two pins are grounded or not for a valve actuator. The two pins are configured as ...
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1answer
27 views

Pull Up Resistor to Substitute SPDT Function

I'm creating a circuit to switch and control between two different analog signals, and I'm doing so with JFETs and a CD4013. If I'm using a guitar pedal stomp switch to pull up or down the data line, ...
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1answer
169 views

i2c Pull up Resistor

I try to run an accelerometer (Data sheet) with this library (link). Bus: I2C and Microcontroller adafruit-feather-m0-adalogger (link) is used. If I wire the accelerometer to the muhC, I just get ...
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1answer
36 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
80 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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1answer
49 views

Would bypass capacitors of a voltage regulator which powers an I2C device and the bus cause issues?

I'm planning on powering a 3.3V I2C sensor and its pull up resistors with a linear LDO regulator. http://www.farnell.com/datasheets/2108564.pdf The output of the LDO aswell as the sensor's power pins ...

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