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

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51 views

Voltage Dividers in a pull-up resistor circuit (why does the pin go to low)

I understand that when the button is in its open state the voltage on the input pin should be fairly close to \$ V_{cc} \$ provided \$ R_1 << R_2 \$ as \$ V_{in} = V_{cc} \frac{R_2}{R_1 + ...
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1answer
53 views

Arduino Mega & LIN Transceiver (MPC2004)

I am trying to connect an Arduino Mega with another device using a LIN Transceiver. I have decided to use a LIN MPC2004 Transceiver for this. I am now trying to understand the reference design of ...
0
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0answers
50 views

Resistor and LED Bias

My question pertains to this sketch of a project called the Quiz-O-Tron 3000. I wired up the proto-sheild and the 4 button switches. When I went back through my inspection and testing of the units, ...
2
votes
2answers
189 views

Using internal pull-ups for I2C on PIC18F

I'm working with a PIC18F46J53 and it was working quite well without any troubles. Suddenly, I found a hindrance on my path. I used RB4 and RB5 pins as I2C bus pins for communicating with an EEPROM ...
0
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2answers
93 views

LM339 : why output +5V

This circuit diagram below is given in my book ( written by Coughlin and Driscoll ) . simulate this circuit – Schematic created using CircuitLab Here it is said that at this condition ...
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2answers
98 views

Can a digital input having internal pull up resistor drive a load?

simulate this circuit – Schematic created using CircuitLab I am working on MC56F8006 DSC . On power up or reset the default state of all GPIOs is inputs with internal pullups enabled. I ...
0
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1answer
75 views

GPIO Pin configurations [duplicate]

I went through the data sheet of STM32F4 and found the pin configuration of GPIOs. I dont understand the difference between these configurations. • Input floating • Input pull-up • Input-pull-down • ...
0
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3answers
434 views

Can I do without I²C pull-up resistors?

I am trying to produce a small circuit, and I am looking to reduce the part count. I recently added an I²C EEPROM which is used once when the system boots up, along with this EEPROM I added two ...
1
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3answers
80 views

Do I need pull-down resistor on Enable pin cd74hc4051

Can I directly connect enable pin to ground? I am not going to use it. datasheet Also can I connect all unused pins of LM324 op-amp to ground through single resistor or what configuration does it ...
8
votes
4answers
3k views

When to use pull-down vs. pull-up resistors

After learning and experimenting with microcontrollers, the concept of pull-up- and pull-down resistors has been understood and saved to my hard drive. I now understand when and how to use them, and ...
1
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0answers
41 views

Internal pull up resistors in a micro-controller vs external pull ups [duplicate]

Micrcontrollers such as PIC describe their pull up resistors as weak pull up resistors, what does weak signify? When/why would I want to use external pull-up resistors on I/O pins that support ...
2
votes
2answers
112 views

How can I design this pull up without wasting current/performance?

I want to move the low side enable switch of my H-bridge onto the high side, because for safety reasons it's better to turn off the tap than plug the drain. I'm powering a 24V, 35W BLDC, so it's ...
3
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2answers
868 views

Internal pullup for input in PIC microcontroller

Im new in PIC world. I want to ask: Do I need external pullup resistor for switches and encoders? When I was using Atmel microcontrollers - I was just turning on internal pullup resistors in ...
0
votes
1answer
84 views

Dallas 1-wire Digital Thermo - issue with strong pullup

I have 2 Dallas/Maxim DS18b20 digital thermometers connected in parasitic-power mode. If I include a strong-pullup as shown on p.6 of the datasheet, the nearer device gives good data; the further one ...
0
votes
1answer
84 views

How to get the full Vcc output from comparator?

I am working on a circuit using a comparator for a school project, but in testing it is not acting as expected. Specifically, the output is not going all the way to the higher rail voltage attached ...
13
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6answers
3k views

What happens if I omit the pullup resistors on I2C lines?

Just now I realized that the I2C data and clock lines (SDA and SCL) must have pullup resistors. Well, I've built a couple of clocks using the DS1307 RTC (see datasheet) according to the schematic ...
1
vote
2answers
433 views

SPI and pullups. Is it ever used in open collector configuration

Is SPI ever wired as open collector in devices calling for the use of pullup resistors? Everything seems to point to it usually being totem pole but I wonder if there are exceptions. The only pullup ...
1
vote
1answer
204 views

How do you size pull-up/down resistors? [duplicate]

The attached photo is pulled from a Piccolo DSP reference design from TI. They use 57.6k pull-up resistors and 2.2k pull-down resistors to allow configuration of boot pins at startup. I've seen all ...
2
votes
2answers
252 views

Convert microcontroller 3.3V output to 6V

I have built an h-bridge from 4 MOSFETS (PHP21N06LT) shown below. This bridge is used for motor speed control in either direction and fast stop. I have a dev board with C8051F020 microcontroller on ...
-1
votes
1answer
63 views

Detect current on intercom

I'm trying to get an input from an intercom and apparently there is GND and another wire for the call. I'd like to know when there's voltage between the call wire and the ground. I'm thinking of ...
3
votes
5answers
212 views

How much current is used with a μC GPIO input and pullup resistor?

I'm trying to understand power budgets a bit better and I have a question regarding pullups. I have a input to a microcontroller that needs to be logic high at all times. The micro goes to sleep now ...
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1answer
171 views

how to, best way to use a linear actuator vs gear system? [closed]

I am wondering what is the best and cheap option to use in a crane like system. a linear actuator or a gear rig system with an engine. the weight at the end could be up to 100 pounds. I was ...
0
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1answer
38 views

GPIO pull up to different level

I am using MSP430F235 which is supplied with 2.5V on DVCC. So, all its I/Os will be in 2.5V level. Now, I want to enable a LDO in which EN pin is tied to a different level (>2.5V is the battery supply ...
2
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4answers
125 views

Pull up circuit current flows?

Im trying to understand how pull up/down circuits works . Let's consider this schematic : I understand that there are two possible current flows : When the button is not pressed, the current ...
3
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1answer
174 views

When a pin needs to stay LOW or HIGH, is it okay to connect directly to VCC or GND?

For example, I'm using an Exar Exar SP3220EBCY-L RS-232 transceiver and the typical application loop back test shows that the EN pin is connected to GND and the SHDN pin is connected to VCC. Should I ...
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1answer
78 views

CMOS 4066 pull up resistor

I'm controlling three 4066 (Quad Bilateral Switch) with two chained 74HC595 (8-bit serial-in, serial or parallel-out shift register with output latches; 3-state) Do I need to use pull up resistor ...
2
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1answer
128 views

I2C Pull-ups with Multiple Power Supplies

If I have an I2C Master with multiple I2C Slaves all on separate 3V3 lines (i.e. 3v3_Master, 3V3_Slave1, 3V3_Slave2... etc.) does it matter which 3V3 line the pull-up resistors on the line connect to? ...
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0answers
1k views

How to assign a pull-up/down resistor in Verilog for inputs?

As a newbie in FPGA world, I realized that it is possible to set pull-up/down resistors in Verilog but I don't know how. I have written my code that works just fine but when I connect my XC3S400 to ...
1
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3answers
186 views

How does this MOSFET circuit work?

The following circuit from a textbook models an inverter implemented by a MOSFET switch. I understand how in the first case Vout is zero, but in the second case(the switch is open), the textbook ...
1
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4answers
508 views

i2C : pull-up resistors “design pattern”, Shielded cable and connector?

I'm designing an arduino based board which will uses I2C port a lot. I want to be able to connect several slave devices, and/or connect several mother boards together (at least 4 would be great). The ...
1
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1answer
232 views

Arduino serial communication RX high

I'm trying to interface with a device via async serial. Here is the power on requirement from the device datasheet: Power-On Reset Requirements When applying power to the DNT900, the /RESET Pin ...
0
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1answer
177 views

LM311 Pull Up Resistor

If I use an LM311 Comparator, then we are required to connect a pull up resistor at the output. Does the square wave output depends on the value of the voltage the resistor pulls up to? Would it be ...
1
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2answers
161 views

Why is pull-up resistor disabled in OUTPUT mode

I noticed in a lot of micro datasheets that the internal pull-up resistor is disabled automatically when the GPIO is in OUTPUT mode, but I'm not sure I understand why. Is a pull up resistor never ...
1
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1answer
96 views

pin is pulled up to something

I was reading 17xx series` data sheet, and I had trouble understanding a specific explanation given for a major number of pins: 5 V tolerant pad providing digital I/O with TTL levels and ...
4
votes
2answers
344 views

How should I alter my PISO shift register circuit so that it works with 3.3v instead of 5v?

I've followed this Arduino guide to build a circuit using a CD4021BE PISO shift register, and 10k pulldown resistors. It works perfectly fine with the Arduino's 5v supply. I then attempted to use ...
1
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2answers
185 views

Basic misunderstanding about dropping down voltage going in a TTL IC using resistors

I'm having serious problems figuring this out. Below is a part of an 8-bit computer schematic. The 62256-70 is a static ram chip. I understand these 8K2 resistors are there to provide a default value ...
3
votes
3answers
180 views

Is it common for internal pull-up resistors to fail? or what would cause them to become intermittent?

I have a board based on an ASIC ARM Cortex-M3 that after months of work suddenly started to report spurious button presses. The ASIC is not our design, but a reputable company's. The buttons ...
8
votes
1answer
271 views

Pull Up and Pull Down Resistor Values [duplicate]

I usually use 10K Ohm resistors for pulling up or pulling down micro-controller lines. This is only because I have tons of them. Recently while looking up pick and place surface mount information I ...
1
vote
1answer
549 views

ATTiny45 Quadrature Decoder Pull-Up resistors

I am trying to use the ATTiny Quadrature Decoder from here. The schematic that I have attached here has two external 10K Pull-up resistors. I have looked into the ATTiny45 datasheet and it seems that ...
4
votes
2answers
410 views

How to deal with multiple pull-up resistors on modules

I was thinking about doing a modules for a development board I did a few days ago that will include spi/i2c interfaces. The problem is that I didn't included pull-up resistors in the MCU pins in the ...
1
vote
2answers
150 views

How and why is “floating input” a valid state for RF/IR encoder IC's?

RF/IF encoder/decoder IC's such as this one, will accept the address-pin in one of 3 states: Floating High Low As per this excellent answer, I believe "Floating" input can assume either High or ...
3
votes
2answers
2k views

I2C pull-up resistors calculation & where to place them

I'm connecting a PIC18F46K22 (master) to a PIC18F4620 (slave) using I2C. The wire between the devices is ~30cm. I'm using 400kHz without slew rate control. Later on, I'll add another 18F4620 on ~5cm ...
7
votes
5answers
647 views

Connecting push button to a controller pin

This problem is decades old but I do not see a direct answer to it on this site. I want the following: This circuit just allows to check the state of the button from inside the micro-controller. ...
5
votes
2answers
183 views

i2c external pullup kills communication

I am using an MCP23017 (which shouldn't matter tho) to extend the number of GPIO pins of an arm based linux computer using i2c-dev bitbanging. It all works fine with wires of a few centimetres. The ...
5
votes
1answer
274 views

i2c on different logic level devices

I'm having a problem making LPC2148 work with SRF10 sensor. LPC is 3.3v device with 5v compatible i2c (at least user docu claims that). On the other side there is SRF10 device which is 5v. I have ...
10
votes
1answer
356 views

Weak internal pullups on microcontrollers and EMI susceptibility

What disadvantages can I run into when using weak internal pullups (100k) on microcontrollers? I'm wondering how susceptible lines (with only parasitic trace/component capacitance) become to EMI ...
7
votes
5answers
5k views

Pull-up and Pull-down Resistor Usage on Input or Output MCU Pins

Are pull-up/down resistors (whether internal or external) only needed for MCU INPUT pins? In contrast, an MCU pin configured as an OUTPUT "knows what level it's at" because it does the driving - a ...
5
votes
3answers
457 views

DS1307-breakout-board

I want to build an RTC clock for the Raspberry Pi. Adafruit has a guide to accomplish this with Dallas DS1307. On the schematic they put a 2.2K resistor between VCC and SCL and do the same for VCC and ...
7
votes
2answers
3k views

I2C pullup resistor calculations

I am trying to drive this I2C LCD display with an ATxmega16A4U microcontroller. Both devices are listed to work with I2C clock frequencies up to 400 kHz. The two devices are the only devices on the ...
23
votes
2answers
842 views

Heuristic explanation of the usage of a pull-up (or pull-down) resistor needed

First, I acknowledge that there are several questions regarding this topic in the forum, however, the answers assume too much background knowledge of electronics to be of use to a true beginner (like ...