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

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3
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2answers
88 views

How to default logic high after a voltage divider?

I have a 5V logic pin coming in that I want to cut down to 3.3V. When the 5V pin is detached, however, I want the pin to default logic high (3.3V). How can I choose R_pu appropriately? V_in = 5V ...
1
vote
1answer
20 views

Atmega 328 with DS1620 thermometer chip. Why is a pull-up resistor needed on the DQ line

I think understand the purpose of pull up resistors in general but in this particular case the DS1620 datasheet says that in the output mode it sources a current of 1ma (see footnote 5 on the last ...
0
votes
1answer
23 views

multiple mosfets controlling individual circuits sharing one pull up res?

i'd like to control several individual circuits using an array of MOSFETs and wondered if they have to have individual pull-up resistors or if they can share one connecting them to ground. Or do the ...
0
votes
1answer
42 views

PICkit3 MCLR to Vdd Pull-Up Resistor

I'll preempt this by saying that I'm a software person whose education (unfortunately) didn't even touch on the most basics of hardware or circuits. I'm attempting to program a PIC16f1709 microchip ...
0
votes
2answers
64 views

Why does my mainboard power the cathode to turn the Power-LED off?

Close to all desktop motherboards have a pin header that is supposed to power an LED on the front of an enclosure with to indicate that the computer is on. In the documentation for my board, these ...
2
votes
2answers
59 views

What use is a pull-up/pull-down with a push-pull output?

For at least some STM32F4 MCUs, push-pull + pull-up/pull-down is a valid GPIO configuration, but what would you ever use it for, and why? I assume there's some saner reason than "I just really felt I ...
13
votes
9answers
2k views

Why does I²C only have pull-up resistors (interview question)?

The interviewer wanted to know why pull-up resistors are used on SDA and SCL when the opposite logic can also be implemented. Is there an explanation for why pull-up resistor usage is the chosen ...
0
votes
0answers
38 views

Why are pullups needed on eMMC data lines?

The JEDEC spec for eMMC shows pullups on both CMD and DAT lines. The pullup for the CMD line is obviously necessary as it sometimes operates in open drain mode, this necessity is represented by Rod ...
0
votes
3answers
38 views

Why does switch change parallel current after junction?

This is an image demonstrating the use of a pull up resistor. I've just started studying electronics and have been learning about ohm's law. Ohm's law says that current within a circuit is equal to ...
0
votes
2answers
92 views

Calculate pull-up resistor for phototransistors

I have made a sensor which uses six IR phototransistors, three per sensor block, opposite it is a matched IR diode(940nm). This is in turn connected to a MCU. The function of the circuit is an ...
1
vote
2answers
149 views

Why are pull-up resistors not drawn this way?

So, I've always been using a pull-up resistor in the configuration that usually appears in textbooks but I can't tell why it isn't drawn in another way. So, basically a pull-up resistor is usually ...
0
votes
2answers
85 views

How to detect input voltage change on specific pin of atmega32? DC jack sensing

I am trying to make an LCD circuit that, eventually, will control an amplifier and display data to the user through the LCD. One of the features I want to include is the ability to show if the device ...
0
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3answers
78 views

How does digital pullups work?

I have lame question. How does digital pullups work? I'm asking because I don't understand DHT11 driver code. Sample code: ...
0
votes
3answers
139 views

Why does a closed circuit with a pull-up resistor output “0”?

I have a switch setup with a pull-up resistor. With the switch open I get a "1" or HIGH output and with the switch closed I get a "0" or LOW output. I understand why I am getting the "1" with it open ...
1
vote
1answer
105 views

i2c communication between cc3200 and at42qt2120

I am trying to do i2c communication between TI's cc3200 and atmel's touch IC AT42QT2120. I am able to read and write to different memory locations of the touch IC, but i am unable to get it's change ...
1
vote
1answer
92 views

Connecting Open-Drain inputs or outputs together with one resistor

I had a couple of quick questions. I am designing a board using 10 IO expanders which I'll use as inputs. Each has an !INT pin which is open drain and pulled high to 5v through a resistor. Can I ...
0
votes
0answers
59 views

STM23 and TLK105 Ethernet acts strange

I am conntecting STM32F107 and TLK105 from Texas Instruments and it works fine most of the time. The problem is a very strange behavior such as: - TLK software reset is not done correctly - Reading ...
0
votes
3answers
203 views

Why use a resistor for Pull-Up? [duplicate]

I just got my first Arduino and had a question about pull-up resistors. I was trying to connect a push-button to the Arduino at pin 2, and if it's HIGH then I write HIGH to pin 13. Now, in the ...
1
vote
2answers
94 views

Is it wrong to write HIGH to a pin used as an open collector?

I'm a software engineer playing with PICs and have an old PS/2 mouse that I am using (successfully), which has CLK and DATA connections as open collectors. So I have configured the internal pullups ...
0
votes
2answers
178 views

Pull up resistor on Schmitt trigger IC input?

I have two different circuits on two different boards. The output of board A, let's say, is optocoupler based and hence, it has a pull up on it. This signal is connected to board B through an ...
0
votes
3answers
86 views

Turn pull-up into pull-down

I have come across the following problem a few times in the past: You have a break-out board where some pins have already been pulled up or down for convenience, e.g. RESET pulled high to keep the ...
4
votes
1answer
387 views

Placement/Location of pull up / pull down resistor?

I have connected a microcontroller GPIO pin, which is intended to be an output, to a DC-DC converter's active high Enable input pin. Since this pin is active high, and because I do not want this ...
4
votes
3answers
644 views

Experiment with pull up/down resistors gives unexpected results

The wikipedia article on pull-up/down resistors provides this image: along with some explanatory text: ... the circuit shown [in the picture] uses 5 V logic level inputs to actuate a relay. ...
1
vote
1answer
109 views

Pull up does not work

I got a breadboard with some logic on it. Including it's own power suppply. It is connected to my Arduino Mega 2560 to fill a shiftregister with some bits. Whenevery my arduino is in a undefind state ...
0
votes
1answer
188 views

Output of a NAND gate

Above is a TTL totem pole output NAND gate. There is a 120 ohm pull up resistor there. Since it is called pull up, can we say that the HI output will be connected to a very high input impedance? If ...
0
votes
1answer
148 views

A question on pull up resistors

I'm wondering why pull up resistors in text books are told such that they pull up the voltage to \$V_{CC}\$. Here is a diagram: When the button is open what will be the input voltage to the micro ...
0
votes
2answers
110 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 + ...
0
votes
1answer
398 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
votes
0answers
61 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, ...
3
votes
2answers
660 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
votes
2answers
246 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 ...
1
vote
2answers
147 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
votes
1answer
176 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
votes
3answers
512 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
vote
3answers
160 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 ...
18
votes
5answers
10k 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. I now understand when and how to use them, and how they work. I've mainly ...
1
vote
0answers
45 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
134 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
votes
2answers
2k 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
129 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
128 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 ...
16
votes
7answers
10k 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 ...
3
votes
2answers
1k 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
331 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
421 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
94 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
360 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 ...
-1
votes
1answer
284 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
votes
1answer
43 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
votes
4answers
168 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 ...