NOR Gate.

The NOR digital logic gate has the opposite output response to it’s input signals as what the OR gate has. The output of the NOR gate will be high for as long as every input is low. If one or more inputs is high, then the NOR gate output will be low.

7402 74HC02 quad 2 input NOR gate integrated circuit with output LEDs schematic diagram by electronzap
7402 74HC02 quad 2 input NOR gate integrated circuit with output LEDs schematic diagram by electronzap

The 7402 integrated circuit (IC) has 4 (quad) NOR gate with 2 inputs each. Don’t forget to power the IC, even though you won’t always see the NOR gate symbol being powered on the schematic. The high speed CMOS version is the most common type of 7400 series IC these days. So I suggest using ICs with part numbers that look like 74HCxx.

I think you will get a much better feel for the NOR logic gate if you build and test out the demo circuit that I show in the schematic and in the video below.

A single pole double throw switch (I simulate one with a jumper in the video) and trimpot make for bad input signals, but they give you more control over the input signal. So I think they are helpful for learning the IC limitations.

When the switch or jumper is to the negative supply (0V ground), and the trimpot is set close to the negative supply, both input are low. That means that the NOR gate output will be high.

Setting the jumper to the positive supply, and/or turning the trimpot close to the positive supply, will give the input that is attached to them a high signal. While one or both of them have a high input signal, the output will be low.

When the output is high, the red LED will light up because the output is close to 5V, and the other side of the red LED is connected to 0V ground. That’s about a 5V difference across the LED.

On the other hand. When the output is low, there will be 0V at the output, and on the other side of the blue LED is +5V. Therefore, the blue LED will light of because it has about 5V across it.

Affiliate link ads to kits with assorted 74HCxx ICs is shown below. the 7400 series IC can be fried relatively easily with static electricity from your body, or miswiring. So, I suggest getting more than 1 of each IC you intend to use. I don’t usually post a particular kit I that recommend because they run out of inventory often.

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