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Functions, Benefits, and Limitations of Pull Up Resistors

Any digital electrical circuit will mostly contain pull-up as well as pull-down resistors if you look into it. In the absence of an input condition, they are employed to properly bias digital gates’ inputs to prevent them from randomly floating around.

Pull-up as well as pull-down resistors use output and input signals for microcontrollers in any embedded system like an Arduino to communicate with different hardware devices.

What Does a Pull Up Resistor Mean?

Electronic circuits utilize pull up resistors to maintain a signal’s known state. To ensure that the voltage across ground and the Vcc is effectively controlled whenever the switch is turned on just like the pull-down type), it is typically used in conjunction with switches and transistors.

It is known as a fixed resistor linked between an input pin as well as the supply voltage; it isn’t an unique kind of resistor. You frequently encounter this pull up resistor within digital circuits since it is so widespread. It merely consists of a resistor linked from such an input to VDD, which is the circuit’s positive supply.

Pull up resistors can be described as resistors that are employed in different logic circuits in order to guarantee a consistent logical level present at the pin. Recall that there are three main logic states in the digital logic circuit: high, low, and floating (which is also called high impedance). When this pin isn’t pulled onto a low or high logic level however it is instead left “floating,” it enters its high-impedance condition.

A micro controller’s input pin that isn’t connected serves as a good example of this. The microcontroller may erroneously interpret the value of the input as either the logical high as well as logical low because it is either a high or the low logic state. The microcontroller’s conundrum is resolved with pull up resistors, which raise the value onto the high state.

How Does the Pull up Resistor Work?

Zero Ohm Resistor

Between the supply voltage as well as the input pin, the resistor is attached. Whenever its mechanical switch seems to be off, the input voltage gets raised to the input voltage level. Additionally, whenever its mechanical switch gets turned ON, the input power is sent straight to ground. To guarantee the level of voltage, the switch is linked with the pull up resistor. The switch regulates the circuit’s input state.

The switch of the power electronics is also utilized inside the circuit in place of the mechanical switch. Since the pin can’t be connected to the supply or ground directly, this pull up resistors are also necessary to prevent short circuits. Other circuit components may be damaged or shorted out if this pull up resistor isn’t connected.

To create a second loop over all the crucial parts and guarantee that this voltage can be well-defined even while this switch has become open, the pull up resistor can be utilized. When there is no input signal, it is utilized to make sure that the wire pulled into a higher logical level. It is a standard type of resistor.

They are straightforward fixed-value resistors attached between this voltage supply as well as the proper pin that, in the absence of a driving signal, specifies the output or input voltage.

This gate input’s voltage is dragged up to that input voltage’s level when this switch is open. This gate’s input voltage passes directly into the ground whenever this switch has been closed. Whenever there’s a low default state of impedance and want to pull this signal into “high,” you must employ the pull up resistor.

What are the Use Cases for Pull Up Resistors?


When connecting the switch and perhaps other input into this microcontroller as well as other several digital gates, the pull up resistors are frequently employed. Lower external components will be required because most microcontrollers feature built-in pull-up programmable resistors.

These microcontrollers can be connected directly to switches. Although certain microcontroller families featuring both pull-up as well as pull-down resistors present, the pull up resistor is typically utilized more frequently than the pull-down resistors.

They are frequently used to deliver a regulated current flow to a resistive sensor before the voltage signal of the sensor output is converted from analog into digital. The pull up resistor is also utilized in the I2C protocol bus, where they allow a single pin to function as either an input or an output. The pin floats in an extremely high-impedance condition when it is not linked to a bus.

  • Pull-down resistors have become less common compared to the pull up resistors in use. The usage of the pull up resistors is described in the list below.
  • The pull up resistor is utilized as interface components between switches and digital circuits.
  • Also, it is utilized in I2C protocol buses in enabling the signal pins to serve as the output or input
  • For the resistive sensors, you can utilize them in controlling the flow of current before the conversion from analog into digital

Choosing the Value for the Pull up resistor

The price shouldn’t be excessive

The input voltage decreases as its pull-up value increases. The voltage must be sufficiently high for this chip to recognize it as the HIGH, as well as logical 1, inputs. For instance, the CD4017 having a 10V power supply needs at least 7V mostly on input to be recognized as HIGH.

It also can’t be very little

The issue arises if, for instance, you select 100, as there is much current passing through it whenever you pressing of the button. The 9V power source gives you 9V across the 100, or 90 mA.

The resistor must be capable of withstanding 0.81W, which is a needless waste of electricity. Most resistors only have the ability to handle 0.25W at a time.

General Rule

Pick the pull up resistors having a value of resistance that is about 10 times lower than the pin’s input impedance (or internal resistance). Frequently, a 10 kΩ pull-up value will work. But keep reading if you wish to know how it operates.

Why Pull Up Resistors are Important?

Pull up and Pull-down Resistors

The pull up resistors are utilized in raising the digital pin’s default state to high or to its logic level, and the pull-down resistor performs the exact opposite, which makes the digital pin’s default pin to become low (at 0 volts).

But why do we need all those resistors whenever the logic pins may be connected directly into the voltage of the logic level or to the ground instead? While the pull-down resistor could successfully control the flow of current from the digital pins onto the ground, the pull up resistor allows controlled flow of current from the source of the supply voltage into the input pins. Pull-down as well as pull up resistors simultaneously hold this digital state in either high or low range.

Use pull-down or pull up resistors if you require a basic logic state but wish to change it in response to user input as well as external peripherals.

What are the Values of Pull Up Resistors?

There are two constraints on the pull-up (as well as pull-down) resistor’s appropriate value. Power dissipation is the primary consideration.

Whenever the switch gets closed, a significant amount of current will pass through this pull up resistor if the value of resistance is extremely too low, heating the component and consuming extra power. Whenever the consumption of low power is required, a powerful pull-up, like it has known, should be avoided. This pin voltage while the switch becomes open is the 2nd factor.

This input voltage may not be sufficient whenever it is an open switch if the value of the pull-up resistance becomes too high and input pin has a significant leakage current. Having relatively weak pull-up is the term for this situation. The input pin’s impedance, which is directly connected to the leakage current of the pin, determines the precise value of the resistance of the pull-up.

The Drawbacks of the Pull Up Resistor

These resistors’ inability to be useful with anything greater than a button is one of their drawbacks. This is due to the resistor’s inability to push current across all of the additional buttons. Additionally, the resistance cannot alter for the other directions because it only permits one current only to flow in one direction. Another circuit, like a “Schmitt trigger,” which has a greater impact than a single push button, can be substituted for it.

We can’t give the circuit enough time to flip from a high to a low when pressing the buttons quickly. As a result, the resistance does not release any energy, and the circuit does not experience any current flow. This is known as “Hold-off.”

Light switches cannot be used with pull up resistors because current just wouldn’t pass through them. As a result, it stops light from turning on. Also,  e avoid using pull up resistors when a switch is off for an extended period of time. Since it won’t let the electricity flow, it must be switched off for longer period of time than usual, which will save money.


When connecting a switch as well as other input to a microcontroller and other types of digital gates, the pull up resistor is frequently employed. There are typically programmable built-in pull up resistors built into microcontrollers, which reduces the requirement for external components.




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