Pull-up and pull-down resistors explained
Summary
TLDRThis 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
🔌 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.
💡 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.
Mindmap
Keywords
💡Pull up and pull down resistors
💡Common ground
💡Data line
💡Digital signals
💡Internal digital switch
💡Floating
💡10K ohms
💡Raspberry Pi
💡I2C
💡Software control
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
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