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

learn more… | top users | synonyms

0
votes
2answers
74 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
110 views

Why pull-up resistors are 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
45 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
votes
3answers
66 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
126 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
63 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
64 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
45 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
187 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
92 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
144 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
82 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
364 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
615 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
103 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
156 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
134 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
92 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
303 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
59 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
542 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
192 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
142 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
149 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
483 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
145 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 ...
15
votes
5answers
8k 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
128 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
121 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
118 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 ...
15
votes
6answers
8k 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
298 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
381 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
89 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
317 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
253 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
42 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
154 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
votes
1answer
213 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 ...
1
vote
1answer
122 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
votes
1answer
223 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? ...
1
vote
0answers
2k 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
vote
3answers
240 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
vote
4answers
667 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
vote
1answer
274 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
votes
1answer
256 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
vote
2answers
193 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 ...