The pullup tag has no wiki summary.
7
votes
1answer
74 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
59 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
108 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
61 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 ...
2
votes
2answers
109 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 ...
6
votes
5answers
215 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
98 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
152 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 ...
8
votes
1answer
175 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 ...
5
votes
5answers
305 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 ...
3
votes
3answers
119 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 ...
6
votes
2answers
213 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 ...
13
votes
2answers
447 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 ...
1
vote
1answer
171 views
i2c problem on LPC2148
I have problem with getting my LPC2148 to work with i2c devices. LPC is on 3.3v bus and i2c devices are on 5v bus with pull-up of 3k6 ohm on either 3.3v or 5v (jumper selection).
What im experiencing ...
8
votes
2answers
236 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 ...
1
vote
3answers
165 views
I2C - Where's the ACK
I'm working on I2C master driver for interfacing a particular peripheral.
The problem I have, is that when the 9th clock arrives, the slave device doesn't pull down the SDA line.
I checked the ...
3
votes
3answers
297 views
Choosing a transistor and resistor for PIC input pin protection from Car Power
Further to my previous question,
Using a PIC to perform switch on and timed shutdowns in automotive environment
I've been pointed at zener diodes and voltage dividers, but I'm now confused by the ...
2
votes
1answer
200 views
Need of External Pull Up/Pull Down for Processor I/O pins
For a particular I/O pin, its been mentioned in the processor data manual that there is Internal pull down, after power on reset, in the device with a default drive state of the pin as tristate(Z).
I ...
3
votes
1answer
146 views
pull up resistor issue?
I have three i2c devices connected to AVR microcontroller. On the i2c bus on master side there are two pull ups with 2k7 ohm.
What im experiencing is that when i power up the microcontroller devices ...
0
votes
1answer
675 views
TLC 5940 PWM driver blank input and pull-up resistor
I've read some of the data sheet for the TLC 5940 and it states the following about the BLANK input:
Blank all outputs. When BLANK = H, all OUTn outputs are forced OFF. GS counter is also reset. ...
2
votes
4answers
615 views
Pulldown resistor on output pin, how does output still work?
On a part I'm working with, it says that you can configure the part to operate in a particular mode by "strapping" a particular pin to ground. That is, it wants you to use a pulldown resistor to pull ...
1
vote
3answers
1k views
Why is this MOSFET's “pullup” resistor necessary?
I'm reading an basic electronics textbook, the chapter on MOSFETs, and it has started with a simple model of the MOSFET as a switch (the "S model"). It shows a circuit like this:
And says: Here we ...
1
vote
1answer
238 views
Pulling a pin to 12 V using 3.3V
I'm building a boost converter and want to implement a shutdown feature. The particular chip I'm using, LM3478, has a shutdown feature which is activated by a high level on the frequency adjust pin. ...
8
votes
1answer
1k views
Plugging a LDR into GPIO pins of a Raspberry Pi
I want to connect a LDR into the GPIO pins of my Raspberry Pi, I know that Raspberry Pi doesn't have an analog-to-digital converter so what I want to do is to signal a HIGH signal (3.3v) on the GPIO ...
2
votes
4answers
326 views
Sharing a pull-up resistor
I have two IC chips. On one chip I have one 10K ohm pull-up resistor and on another chip I have three 10K ohm pull-up resistors.
At first I was using four through hole pull-up resistors. Then I ...
6
votes
3answers
507 views
Why would an input pin have both a pull-up and pull-down resistor?
In his answer detailing the various types of input pins, Russell McMahon leaves the following note [referring to input pins]:
there are special cases where a resistor to high and low at once is ...
4
votes
3answers
3k views
Logic Conversion 3.3V to 5V (Current Related) 74HC 74HCT
A beginner style question.
I'm attempting to perform some logic level conversions on 3.3V signals to 5V using the 74HC4050D powered at 3.3V and 74HC541 powered at 5V. Is it OK to directly connect the ...
1
vote
1answer
84 views
Master included as device on I2C bus?
Hi When calculating the pull up resistor value using the formula R = 50 / d, where d is the number of devices on the bus, is the master considered a bus device?
for e.g. If I have a micro controller ...
4
votes
2answers
1k views
Why does a pull-up resistor not stop current flowing to the input pin when the switch is open?
Sorry this is such a silly question, but I can't seem to understand this. In the third diagram here it shows a pull-up resistor.
I understand that when the switch S1 is closed, current is pulled ...
2
votes
2answers
1k views
Are I/O pin internal resistances equal to the Thevenin resistance?
I'm trying to find the Thevenin resistance of an I/O pin for the ATmega644. I see on the datasheet that there is a 20-50 kohm range of internal pull-up resistance. So with that, I can create a ...
20
votes
3answers
5k views
How do I calculate the required value for a pull-up resistor?
There are many tutorials that use a pull-up or pull-down resistor in conjunction with a switch to avoid a floating ground, e.g.
http://www.arduino.cc/en/Tutorial/button
Many of these projects ...
8
votes
3answers
2k views
Recommendation for default settings for unused pins on an STM32 (ARM Cortex M3) - pull up/pull down?
We are currently using various variants of the STM32 microcontroller family. I would like to know the following:
1) What are the recommended default settings for pins of the microcontrollers in ...
6
votes
4answers
936 views
Why are pull up resistors more common than pull down resistors?
I noticed that pull up resistors are much more common than pull downs, why?
For example, the Arduino's MCU has internal pull ups but these tend to invert the physical logic of things you are working ...
1
vote
1answer
143 views
Mismatched Pull Up Resistors
Is it OK to have pull up or pull down resistors which aren't all the same value (if you're running low on components for example)? I can't think of a reason it should affect simple logic circuits.
...
