How does a pull up resistor work in a logic gate?

How does a pull up resistor work in a logic gate?

With a pull-up resistor connected, the output still works in the same way as a normal logic gate in that when the output transistor is OFF (open), the output is HIGH, and when the transistor is ON (closed), the output is LOW. Thus the transistor turns ON to pull the output to a LOW level.

What’s the difference between a pull up and pull down resistor?

These unused logic inputs can be tied together or connected to a fixed voltage, using a high value resistor to either the Vcc voltage, known as pull-up or via a low value resistor to 0V (GND), known as pull-down. These unused inputs should never be left just floating about.

How to trigger a 12 V relay with Arduino?

I am trying to trigger a 12 V relay with an arduino input. All I am doing in the Arduino sketch is to make pin 13 go high and low every 1 sec (1000 ms). The relay refuses to get triggered. Can someone please tell me what am I doing wrong? Struggling with this for way too long. Adding to what other people said in their answers.

What’s the difference between low and high level triggered relays?

Low-level triggered will allow the current to go through the power line when the control signal is below a certain voltage. High-level triggered will allow the current to go through the power line when the control signal is above a certain voltage. Am I right? A mechanical relay needs current to pass through its bobin to trigger.

Can a TTL gate be connected to a pull up resistor?

Two or more open-collector outputs of TTL gates can be directly connected together and tied through a single external pull-up resistor. The result is that the outputs are effectively AND’ed together as the combination behaves as if the gates were connected to an AND gate. This type of configuration is called wired AND logic.

When does the current flow out of the logic gate?

Likewise, when the input of the logic gate is LOW, the current flows out of the TTL input as the input acts basically as a path connected directly to Vcc. This input current, I IL (max) is negative in value as it flows “out-of” the gate and for most TTL 74LSxxx inputs, has a value of -400μA, (-0.4mA).

Why do microcontrollers use pull up and pull down resistors?

As you stated, using pullup/pulldown resistors on pins expected to be output pins can be there to guarantee an input state. This is done to mitigate firmware/MCU failure, but will only work to protect against Hi-impedance state (basically the pin is configured as input by accident).

What should be the resistance of a pull down resistor?

For pull-down resistors, it should always have a larger resistance than the impedance of the logic circuit. Or else, it will pull the voltage down by too much and the input voltage at the pin would remain at a constant logical low value regardless of whether the switch is on or off.

Can a gate be made with only a diode and resistor?

If the anode is at a lower voltage than the cathode, the diode is reverse biased, its resistance is very high, and no current flows. We can construct simple gates with nothing more than two or more diodes and a resistor. See Figure B.6.

How is the base of a transistor held low?

When a logical input to the SN7407N is high, the output of its internal NOT gate is low. Since the output of the NOT gate is connected (through a resistor) to the base of the internal NPN transistor, the base of the transistor is held low.

How does a NPN resistor work in a PNP transistor?

With the input low, the output of the internal NOT gate is high, which pulls high (and turns on) the internal NPN transistor, creating a low-impedance path from the output pin to ground. A small amount of current flows through the PNP transistor, through the 1 k? resistor, and through the NPN transistor to ground.

Why do I need a pull down resistor?

The pull-down resistor must have a larger resistance than the impedance of the logic circuit, or else it might be able to pull the voltage down by too much and the input voltage at the pin would remain at a constant logical low value – regardless of the switch position. The appropriate value for the pull-up resistor is limited by two factors.

What’s the difference between Pull Up and pull down resistors?

Just like the pull-up resistor in the first figure, the pull-down resistors in this circuit also ensures that the voltage between VCC and a microcontroller pin is actively controlled when the switch is open. Unlike the pull-up resistor, the pull-down resistor pulls the pin to a low value instead of high value.