Pull-up and pull-down resistors explained

Summary

This video explains the function and importance of pull-up and pull-down resistors in digital communication between devices. It illustrates how these resistors ensure a clear high or low signal state by connecting the data line to either the power supply or ground through a switch. The video clarifies that without these resistors, the data line would float undefined, leading to communication errors. It also touches on the sizing of these resistors and mentions that many microcontrollers, like Arduino and Raspberry Pi, have integrated pull-up and pull-down resistors for standard communication protocols.

Takeaways

• 🔌 Pull-up and pull-down resistors are essential in digital communication to ensure clear signal transmission between devices.
• 🌐 Communication typically requires at least three lines: power, ground, and data, with some special cases using only two lines.
• 📶 A high signal is transmitted by connecting the data line to the power supply, while a low signal is achieved by disconnecting it, allowing it to float.
• 🔩 Without pull-down resistors, a floating data line can cause undefined signal levels, leading to miscommunication.
• 💡 Pull-down resistors pull the data line voltage level down to the ground, ensuring a clear low signal state.
• ⚠️ Directly connecting data to ground can cause a short circuit, damaging the devices, hence the need for a resistor.
• 🔄 Pull-up resistors work in a similar fashion but pull the data line up to the high voltage level when needed.
• 💻 Many microcontrollers and microcomputers, like Arduino and Raspberry Pi, have integrated pull-up and pull-down resistors for common communication protocols.
• 🛠️ For protocols not natively supported, external pull-up or pull-down resistors may be necessary, or they can be enabled via software.
• 📈 The choice of resistor value, typically around 10K ohms, can vary based on specific requirements and is a topic for more advanced discussions.

Q & A

What are pull up and pull down resistors?

Pull up and pull down resistors are used in digital communication to ensure that a signal line has a defined logic level when it is not being actively driven by a device. A pull up resistor pulls the line to a high level (connected to V+), while a pull down resistor pulls it to a low level (connected to ground).

Why are pull up and pull down resistors necessary in digital communication?

They are necessary to prevent the signal line from floating at an undefined voltage level, which can cause incorrect signal interpretation by the receiving device. They ensure a clear high or low signal state when the line is not actively being driven.

What is the purpose of a pull down resistor in a digital circuit?

A pull down resistor is used to ensure that the data line is at a low logic level (0) when the internal switch is open, by pulling the data line voltage down to ground.

How does a pull up resistor function in a digital circuit?

A pull up resistor functions by pulling the data line to a high logic level (1) when the internal switch is open, by connecting the data line to the power supply voltage (V+).

What is the typical value for a pull up or pull down resistor?

The typical value for a pull up or pull down resistor is around 10K ohms, but it can also be as low as 1K ohms depending on the specific requirements of the circuit.

Why should the pull down resistor not be zero ohms?

A pull down resistor should not be zero ohms because it would create a direct short circuit between the data line and ground, potentially damaging the circuit components when the switch is closed.

What is the role of a pull up resistor in a communication protocol like I2C?

In a communication protocol like I2C, a pull up resistor ensures that the data lines (SDA and SCL) are at a high logic level when not being actively driven, which is necessary for proper communication between devices.

Can pull up and pull down resistors be enabled or adjusted through software?

Yes, on some microcontrollers or microcomputers like a Raspberry Pi, it is possible to enable or adjust pull up and pull down resistors through software settings.

Why are pull up and pull down resistors integrated into microcontrollers like Arduino or Raspberry Pi?

They are integrated to facilitate easy and reliable communication protocols like I2C, SPI, or UART, where the correct logic levels need to be maintained for proper data transmission.

What is the significance of having dedicated pins for communication protocols on a Raspberry Pi?

Dedicated pins for communication protocols on a Raspberry Pi ensure that the correct pull up and pull down resistors are in place for those protocols, simplifying the connection and communication with peripheral devices.

What should be considered when choosing the value of a pull up or pull down resistor?

When choosing the value of a pull up or pull down resistor, one should consider the desired rise and fall times of the signal, the capacitive load of the circuit, and the power supply voltage to ensure proper signal integrity and device compatibility.

Outlines

00:00

🔌 Understanding Pull Up and Pull Down Resistors

This paragraph explains the concept of pull up and pull down resistors in digital communication. It discusses the necessity of a common ground for communication between two devices and the use of data and power lines. The paragraph describes how a device sends a digital signal by connecting the data line to the power supply (high level) or disconnecting it (low level). However, when disconnected, the data line floats and is undefined. To ensure a clear low level, a pull down resistor is used to connect the data line to the ground. The paragraph also touches on the potential issues of directly connecting data to ground and the appropriate sizing of the pull down resistor, typically around 10K ohms. It concludes by introducing the concept of a pull up resistor, which is used to ensure a high level when the data line is disconnected from ground.

05:01

💡 Practical Applications of Pull Up and Pull Down Resistors

The second paragraph delves into practical applications of pull up and pull down resistors, particularly in microcontrollers and microcomputers like Arduino and Raspberry Pi. It mentions that these devices often have integrated pull up and pull down resistors for standard communication protocols, ensuring proper signal levels during data transmission. The paragraph also explains that for protocols like I2C, SPI, or UART, dedicated pins on these microdevices already have the necessary resistors in place. Additionally, it discusses the option to emulate I2C on a virtual pin, which would require external resistors. The paragraph concludes with a reminder about the importance of these resistors in electronic communication and encourages viewers to subscribe for more content on electronics and IoT.

Keywords

💡Pull up and pull down resistors

Pull up and pull down resistors are electronic components used to ensure a defined logic level on a data line when no other signal is present. In the context of the video, these resistors are crucial for digital communication between devices. A pull up resistor connects the data line to a positive voltage (V+), ensuring a 'high' state when the line is not actively driven. Conversely, a pull down resistor connects the data line to ground, ensuring a 'low' state. The video explains that without these resistors, the data line could float at an undefined voltage, leading to unreliable communication.

💡Common ground

A common ground refers to a shared reference point in an electrical circuit, which is necessary for the proper functioning of communication systems. In the video, it is mentioned that for communication between two devices, having a common ground is essential to ensure that the voltage levels are consistent and that the devices can interpret signals correctly.

💡Data line

A data line is a conductor in a circuit that carries information or data between components. In the video, the data line is central to the discussion of pull up and pull down resistors, as these resistors manage the state of the data line when it is not being actively driven by a signal.

💡Digital signals

Digital signals are electrical signals with discrete levels, typically representing binary data (highs and lows). The video discusses how pull up and pull down resistors are used to ensure that digital signals have clear and defined states, which are essential for reliable communication between devices.

💡Internal digital switch

An internal digital switch is a component within a device that can connect or disconnect a data line from a voltage source to create a digital signal. The video uses the analogy of a simple switch to explain how devices use internal switches to control the state of the data line, which is then influenced by pull up and pull down resistors.

💡Floating

In electronics, 'floating' refers to a state where a circuit or part of a circuit is not connected to a defined voltage reference, such as ground or a power supply. The video explains that without pull up or pull down resistors, a data line can become floating, which can cause undefined signal levels and communication errors.

💡10K ohms

10K ohms refers to a resistance value of 10,000 ohms, which is a common value for pull up and pull down resistors. The video suggests that a 10K resistor is a typical choice for these applications, balancing the need for a defined signal level without drawing excessive current or causing voltage drops.

💡Raspberry Pi

The Raspberry Pi is a series of small single-board computers used for various electronic projects. The video mentions that the Raspberry Pi has integrated pull up and pull down resistors for certain communication protocols, which simplifies the design of circuits that use these protocols.

💡I2C

I2C, or Inter-Integrated Circuit, is a multi-master serial communication protocol. The video notes that devices like the Raspberry Pi have dedicated pins for I2C, which include the necessary pull up and pull down resistors for proper communication.

💡Software control

Software control refers to the ability to manage electronic components through programming rather than hardware connections. The video mentions that some boards allow enabling or disabling pull up or pull down resistors through software, providing flexibility in circuit design.

Highlights

Explanation of pull up and pull down resistors in digital communication.

Importance of a common ground in device communication.

Role of data line in transmitting digital signals.

Use of internal digital switch to connect data line to power supply for high signal.

Necessity of a low level signal and the issue of undefined data levels.

Introduction of pull down resistors to ensure a low signal level.

Potential risks of directly connecting data to ground.

Sizing of pull down resistors and their typical values.

Concept of pull up resistors for high signal levels.

Function of pull up resistors to prevent short circuits.

Default values for pull up and pull down resistors.

Presence of integrated pull up and pull down resistors in microcontrollers.

Use of dedicated pins for specific communication protocols on devices like Arduino and Raspberry Pi.

Emulation of I2C on virtual pins and the need for external resistors.

Ability to enable pull up/down resistors via software on some boards.

Summary of the purpose and usage of pull up and pull down resistors.

Encouragement to subscribe for more electronics and IoT content.

Transcripts

welcome to PL diot in this video we will

clarify what are pull up and pull down

resistors and what they are good for

when talking about pull up and pull down

resistors we normally talk about

communication between two devices at

least no matter which type of

communication you normally want to make

sure to have a common ground beside that

you obviously have some kind of data

line and obviously also some kind of

power line so as a minimum for

communication we would have three lines

yes sometimes there are specialities

where you have only two lines and you

emulate the actual communication onto

the power supply line but that's a

really special case so whenever we want

to send a signal and we're talking in

this case specifically about digital

signals it will look something like this

we have highs we have lows but nothing

in between in case device one wants to

communicate this specific signal to

device 2 it will do the following it

will use an internal digital switch I

will just illustrate this with a normal

switch and device one will now connect

the data line to the power supply line

so device two will now see exactly this

level the high level the data line is

connected to the potential of the power

supply line which is in our case let's

say 3.3 or 5 Vols depending on what

device you're on but now there's the

second level the low level or zero level

to achieve this device one will open the

switch and so for cut the connection

between data and v+ therefore device 2

should see now zero the low level on the

data line I guess sounds quite fine once

I explain it but actually the device 2

will not see the low level because data

is now undefined once you look at the

data line you can see that it's actually

floating in space not connected to

anything not connected to any voltage

level so device two is not seeing this

low level it's actually seeing something

in between it could be this but it could

be also that the point is that the data

level of the signal is undefined it's

floating so what we have to do we have

to pull down this voltage level to the

low level to do so we will connect or

introduce a resistor between data and

ground the pull down resistor so the

name makes actually a lot of sense

because this resistor will pull down

this logic level to low to zero to

ground You could argue that there is a

resistor are in between data and ground

and so far it's not exactly at ground

but as long as data is not connected to

anything else but as long as data is not

connected to anything else it's actually

on the same voltage level as ground You

could argue as well that we should

connect ground and data directly but be

careful with that because what you're

basically doing is you're connecting

directly data the ground which is a

shortcut so this would work okay as long

as the switch is open but as as soon as

you close the switch again you're

basically short cutting v+ directly to

ground which will obviously destroy your

pins on your device one as well as on

your device two so you want to make sure

that your pul down resistor is not zero

but also not incredibly big what you

normally see is something like 10K

10,000 ohms could be also down to 1,000

ohms there are different reasons and

requirements why you want to choose your

pull down resistor on a certain level

but this is something for an advanced

video so this is the pull down resistor

why you need it and how you roughly size

it but obviously if there's pull down

there's also a pullup resistor so we

have a similar setup but in this case we

have our signal which is going to be

introduced between data and ground with

a switch between data and ground so by

default we are connected to ground which

would be our low signal here at the

beginning this is clear and if we want

to have a high signal we will open the

switch so to Signal the high level to

device 2 but again just because we're

not longer connected to ground doesn't

mean that we're exactly on low this is

again an undefined State data is now

again free floating in space so what we

want to do we want to introduce a

resistor between data and v+ between

data and our voltage high level which

will now pull up data to v+ and in case

switch is closed it doesn't hurt we have

no direct connection between v+ and

ground because our resistor our pull-up

resistor is in between again around 10K

would be a default value which will make

sure that you have no shortcut no energy

losses no current losses between v+ and

ground just because your communication

is going on that's roughly what you want

to do by the way in case you're working

on an audo or Rasberry Pi or roughly all

established microcomputers or

microcontrollers you have integrated

pull up and pull down resistors So

within your Arena within your Rasberry

Pi there are on board already tiny

resistors ready for you to use so

whenever you have a communication going

on let's say I Square C your

microcontroller or microcomputer is

automatically using the right pull up or

pull down resistor depending on the

communication protocol to make sure you

have proper communication that's by the

way the reason why you have natural ice

CRC or SPI pins on your Raspberry Pi or

arino because those pins are dedicated

to this specific communication protocol

left the right pull up and pull down

resistors in place obviously there are

other reasons around but this is one of

them what you can always do with your

Rasberry Pi in case you need several ice

sare SE buses you can emulate ice s c on

a so-called virtual pin so you can

choose any gopo pin and emulate iqu C on

this pin but in this case you need to

make sure to have external pull up or

pull down resistance established

depending on which communication

protocol you're talking about if it's

ice CR C IPI or whatever on some boards

you also have the possibility to enable

pull down or pull up resistors within

your software which is obviously quite

convenient anyway this is it you learned

what is a pull up and pull down resistor

you learned how to use them when you

need them and why you need them I hope

you liked it and please make sure to

subscribe to the channel to make sure to

learn more about electronics and iot in

the meantime thanks for watching and see

you next time