A Pulldown Resistor brings a line down to a voltage (Typically Ground Potential), while allowing the line to be pulled up.

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122 views

Pull Up/Pull Down Resistor Confusion

I have googled the crap out of this but I can never find a good answer. In a circuit with a pull up resistor, why is the input pin fed current with a resistor? A pull down resistor circuit doesn't do ...
0
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2answers
188 views

Should the output of logic gate have pull-up or pull-down resistor

I am a bit confused whether my chosen AND gate should have pull-up or pull-down resistor on the outputs, as I don't see any sentence containing words like pull-up/down or sink or source ... but as far ...
0
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1answer
269 views

stm32f4 pull up resistor value

I'am working with Stm32f4 discovery board , i need to know the right value of the pull up resistor on the GPIO port all there is on the datasheet is : week pull up Thank you
0
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0answers
47 views

Unable to determine why clock signal is being pulled down

I have a clock signal coming out of an SPI source. This source has an output resistance of 400 ohms at 8MHz which was measured and output voltage of 1.9V peak-to-peak. The clock signal travels to a ...
1
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1answer
34 views

Pulldown doesn't seem to affect inverter?

I have a relay/optoisolator circuit which is connected to a microcontroller. The input/output is controlled by a physical slide switch. I expected this to turn off the relay and status light ...
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1answer
82 views

Pull Up/Down vs High/Low Pull [closed]

Is pull up the same as high pull? Is pull down the same as low pull? If they are different what is the difference? These two terms are all mentioned in this guide and it is kinda confusing.
1
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2answers
71 views

Pull up/ Pull down resistor

I am using an external pullup resistor on my input pin, and a switch connected to GND. It is like in the picture below. In the below picture, when the switch is open, the MCU input pin will see a ...
3
votes
1answer
67 views

Electron flow with pulling resistors

I'm very confused on the idea of pulling resistors. I get that they set the default voltage to a value so that you don't get a floating high or low value, but I don't get the application in TTL. So ...
7
votes
2answers
454 views

Why does atmel use 39R pull-down resistor?

I recently bought an SAM4S XPLAINED Board to get a bit experienced with ARM. There is an external RAM on this board and there is a 39R pull-down resistor on PIN6 which is the /CS1 line of the RAM. ...
1
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1answer
36 views

Question about comparator MAX912 latch enable

http://www.hep.uiuc.edu/cleo/trig3/boards/tile/vme021d_data_sheets/max912.pdf I am using this MAX912 as comparator. There is a latch enable in this circuit which according to the datasheet, output is ...
1
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2answers
71 views

Safely connecting GPIO input to output

I'm working on piece of software for Raspberry Pi and I'm writing an integration test. One of the cases requires that I'm able to read a state of one pin on another (basically if one output pin is ...
1
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1answer
189 views

Enabling Freescale IMX6 pull down registers on an input pin

I'm looking for a way to enable the pull down resistor on a Freescale iMX6 MCU. I'm running a Linux distribution on it and usually interact with the hardware using a higher-level language, so I'm ...
0
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3answers
60 views

Can this active-high scenario be achieved without an external pull down resistor

If I understand correctly, few microcontrollers offer internal pull down resistors on their input pins but almost all allow for internal pull up resistors to be configured. Why exactly is that ? I ...
0
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2answers
65 views

Isolating GPIO's using diodes

Schematic The arrows are GPIO's I want to be able to close multiple switches at once in any particular order in order to manipulate GPIO's manually. I could give each GPIO its own resistor, but when ...
0
votes
2answers
123 views

does CompactRIO modules have builtin pull-up/down resistors

I have Compact RIO 9076 with 4 different modules: NI-9205 (Analog Input), NI-9264(Analog Output), NI-9402 (Bidirectional Digital I/O), NI-9403 (Bidirectional Digital I/O). I have several 3rd party ...
1
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1answer
998 views

FPGA floating pins, when place pull-up/down resistor on Input or Output

I've looked my FPGA datasheet and found that there is no pull-up/down resistors on it's pins(just a pull-up but that need to be enabled). So, when I power up my circuit I've for a "big" amount of time ...
0
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1answer
152 views

Is it possible to detect high impedance at FPGA input?

I am using a FPGA development board which have neither pull-up nor pull-down resister at the input side. VHDL code that I am developing has to detect either logic zero or logic one and to do ...
0
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2answers
231 views

What is the wiring for a pull-down resistor on the Or gate?

Is this wiring and resistor the best choice as a pull-down resistor? Is it necessary to put the pull-down resistor(s) on all inputs and outputs? I put a 10K Ohm resistor connected to the chip ground. ...
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2answers
1k views

What does pulldown resistor from Arduino's output pin to ground do? Is it necessary?

I came across the first picture below. But I am not able to find out how such arrangement is necessary or beneficial when you want to switch a load with an N channel MOSFET? Question number 1: Is ...
0
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3answers
59 views

Low leakage current methods of initializing pin inputs at power up

Suppose I have an IC that has a standard level triggered input pin. I need this pin's state to be setup immediately at power on at a time when my MCU's GPIOs may not have established levels. What are ...
0
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3answers
318 views

Pull-down resistor ; why is it crucial

These 3 diagrams represent 3 test cases. Dia 1: When I perform an analogRead of analog port 0, then I get a high value obviously. According to the manual, the ...
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3answers
330 views

pull down resistor in PIR circuit

I have an motion sensor circuit. The circuit calls for a voltage of 2-15 dc volts. On the PIR data sheet the source pins calls for a pull down resistor of 47K at 5 volts. My question is if I use 8 ...
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1answer
436 views

Connect arduino to COM pin of a NO NC button

I probably have a basic question but i'd like a confirmation on my solution. I have finished my arduino breadboard prototype which is using some basic momentary push buttons along with pull down ...
0
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2answers
77 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 ...
0
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1answer
162 views

Weak pull down for SPI

I am using Arduino(does not matter) and 8 x 12 bit-ADCs to read some values. I created a prototype which consists of a Shift Register(SR) and all outputs of SR are connected to individual ADC's ...
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1answer
104 views

Pull down/pull up resistor for 5v input

I need to implement a pull-down resistor for a project, but I am unsure of what resistor to buy. My circuit deals with 5v inputs. Essentially, I am trying to make this: keypad scanner. Here is a ...
0
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2answers
248 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 ...
2
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2answers
193 views

Simple SPST Switch Circuit - Pull-down Resistor VS. Current Limiting Resistor

Super Noob EE question: Here is my quick draw-up of my SPST switch circuit schematic. I know I probably did not do this right, but if it gets the idea across, then thats good enough for me atm. ...
4
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1answer
224 views

MCU pull down input push button with interrupt ESD issue

I have an MCU operated at 3 volt with an input pin that is floating by default. I have an external pull down circuit with a 10K resistor connected to the I/O pin. I also have it tied to VCC using a ...
0
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0answers
66 views

How much resistance should a pull resistor include? [closed]

How much pull to ground resistance do I need? Is the amount you need variable? How did you figure this out? (Where can I learn too) Any references I should look to? So sorry for my large host of ...
2
votes
1answer
201 views

LED's connected to a relay remain on?

I built a simple project with an Arduino board. I use the board to read analog input values from a rotation sensor (potentiometer), and use the values to determine which SSR relay on a module to turn ...
0
votes
3answers
110 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
669 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
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3answers
906 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. ...
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2answers
169 views

What is the need for a pull-down resistor in this schematic?

here at the second page: http://www.skyeinstruments.info/index_htm_files/W200P%20Windvane.pdf there is an external 470k resistor in parallel with the measuring device. it seems like the manufacturer ...
0
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1answer
123 views

DS1302 realtime clock - pulldowns required?

I'm trying to wire up a DS1302 realtime clock, one of these: to a parallax propeller board. The datasheet says (page 4) that pulldowns are integrated into each of the main lines (looks like 3 ...
0
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1answer
338 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 • ...
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3answers
361 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 ...
26
votes
5answers
21k views

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

After learning and experimenting with microcontrollers, I've understood the concept of pull-up- and pull-down resistors. I now understand when and how to use them, and how they work. I've mainly used ...
1
vote
1answer
494 views

Using an internal pull-down resistor on a microcontroller

I am using an STM32 microcontroller. If I configure a pin as input with a pull-down resistor for use with a button, do I also need to put a resistor between the input pin and VDD?
0
votes
1answer
101 views

The proper way to store bits in JK flip flops [closed]

Currently I'm working on a contraption where when a button is pushed, it briefly creates a 4 bit binary sequence. I want to have this binary sequence, 0000 all the way up to 1111, stored properly in ...
0
votes
3answers
938 views

Solar cell powered supercapacitor charger with strange output voltage regulator problem

I have a strange problem in a low power circuit design. I designed a buck-boost converter as a maximum power point tracking circuit (control the output of solar cell within a small voltage range ...
2
votes
3answers
317 views

Murata OKR-T/10 pulldown value

On the Murata OKR-T/10, the data sheet specifies a 49kohm pulldown resistor but I've seen people using a 1k. Is there a more correct value or does anything 1k or above work just as well?
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vote
1answer
153 views

Effects of “loading down” Voltage-Divider Circuits

Hello I am currently a beginner in the world of electrical engineering and would like some help on voltage-divider circuits. My question mainly concerns the "loading down effect". Can someone please ...
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votes
2answers
519 views

Voltage divider circuit and the Pull-down resister

I am reading about the pull-down resister here. Question 1. The circuit schematic of a light sensor using a voltage divider circuit is shown as: LDR has a resistance of 0.5k\$ \Omega \$ in ...
1
vote
1answer
647 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 ...
-1
votes
1answer
139 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 ...
2
votes
2answers
3k views

How does the pull down resistor work in this circuit?

Here's an image from another question: I get what the pull down resistor is there to do, but I don't really understand exactly how it works. When there is no voltage applied through the base wire, ...
1
vote
1answer
268 views

Separate PICAXE Download board Serial In pull down resistor

I have a PICAXE (20M2) project that I am working on and I have two separate boards one programs the chip, the same chip then gets transferred to the other board, to which the peripherals (LEDs, ...
3
votes
4answers
230 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 ...