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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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
66 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 ...
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2answers
58 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 ...
1
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2answers
68 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. ...
2
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1answer
91 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 ...
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0answers
64 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
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1answer
113 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
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3answers
84 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
375 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
630 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
121 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
84 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 ...
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0answers
84 views

WeMo Wireless Light Switch US convert to be used in UK?

I am in love with this thing and just cannot believe that it runs 120V 15A. Step down transformer would be too big since this thing should fit into the wall. http://www.belkin.com/us/p/P-F7C030/ ...
0
votes
1answer
161 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
154 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
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5answers
9k 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
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1answer
198 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?
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1answer
73 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
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2answers
610 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
272 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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1answer
102 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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2answers
402 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 ...
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1answer
314 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
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1answer
91 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
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2answers
992 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, ...
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1answer
175 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, ...
2
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4answers
160 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 ...
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1answer
748 views

Pull down resistor not pulling current down to 0 V? - Arduino + LED's

I was recently connecting an LED strand to my Arduino nano using the following wiring diagram: I was using 10k ohm pulldown resistors in order for the LED's to be off when the Arduino is outputting ...
-1
votes
2answers
265 views

Getting rid of floating input in a logic level converter

Is it possible to make the output of this circuit 0V, when the input is floating as shown in the picture . I tried adding a pulldown resistor to the input, but it only worked at a very low value(100 ...
3
votes
1answer
222 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
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1answer
130 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 ...
1
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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 ...
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0answers
944 views

ULN2003A Darlington array behavior

I'm testing a ULN2003 Darlington transistor array (Datasheet Here). simulate this circuit – Schematic created using CircuitLab With GND or 5V input it works fine, but if I unplug an ...
1
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2answers
443 views

How to use a transistor to pull a pin low?

I'm trying to make a simpler approach to flash LPC1114 MCU. If the MCU is reset while pin1.1 is held low it enters bootloader mode. I'm using a simple arduino sketch to drive reset & 1.1 pins via ...
1
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1answer
102 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 ...
11
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5answers
6k views

What makes a pull-up/down resistor strong or weak?

A "strong" pull (up/down) resistor would be one of a relatively low value, while a "weak" one would be of a relatively high value. For example, a pull-down resistor would be used to keep an I/O pin ...
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vote
2answers
293 views

Can a pull down be used to tie a line to ground?

From my recent introduction to pull-up/pull-down resistors, I understand that an input with a pull-down will stay low instead of floating. Since the pull-down resistor leads to ground, couldn't I ...
9
votes
1answer
333 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 ...
6
votes
4answers
2k views

Why use a pull-down resistor with a LDR and microcontroller?

I am looking at this: http://learn.adafruit.com/photocells/using-a-photocell It's connecting VCC <-> LDR <-> resistor <-> GND. And the analog ...
1
vote
2answers
159 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 ...
1
vote
1answer
376 views

Logic NOT gate only works with Oscilloscope probe connected

I have a very simple circuit that is misbehaving in a way that I cannot explain with my very limited experience. The circuit that consists of a motion detector: ...
-2
votes
3answers
1k views

How do I calculate the required value for a pull-down resistor in a PWM circuit?

I'm using 74HC595 with SoftPWM to control some LED's. When the 74HC595 is off, its outputting about 0.57v, enough to turn my LED's on somewhat. How do I work out the value of the pull-down resistor ...
5
votes
1answer
2k views

Using Piezo Vibration Sensor with Pull-Down Resistor - Arduino

I'm using a MEAS piezo sensor (this one: https://www.sparkfun.com/products/9196) to detect very slight vibrations, but I'm having trouble selecting a pull down resistor that allows it to be sensitive, ...
8
votes
5answers
9k 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 ...
4
votes
2answers
572 views

Pull-down resistor value for FSR's voltage divider circuit connected to Arduino

I am working on a project which includes two FSRs (force sensitive resistors) connected to an Arduino Uno. I have each FSR setup as in http://www.instructables.com/id/FSR-Tutorial/?ALLSTEPS, but each ...
24
votes
2answers
970 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 ...
3
votes
1answer
1k views

Pull down resistor for Arduino input to read LOW when no voltage from switch

I'm building the Arduino spaceship interface from the project book and everything works fine. It involved connecting 3 Arduino outputs to 3 leds, and 1 Arduino input to the a switch. For a photo of ...
0
votes
1answer
1k views

Pull-down resistor with ADM485

I have ADM485 already mounted and an output of some device, buffered by CD4050BM. For the circuit to be safe for the RS485 bus, the ADM transiver initially should either be in Z-state or read-state. ...
3
votes
2answers
315 views

Increase resolution of voltage divider

I have a lead-acid battery on which I am using a voltage divider to measure the remaining charge. Its my understanding that an example battery could discharge from 100-0% over say 10.5V - 12V. ...
13
votes
3answers
898 views

Must IO pins each have their own pull-up/down resistor?

A very basic question: Must each IO pin of a microcontroller that is serving as an input from a switch or jumper have its own pull-up/down resistor? In this example, each pin is pulled down by a ...