Universal Logic Gates (NOR, NAND) – B1P24

We’ve learnt about the basic logic gates in the previous video and we’re now going to use them to build two new gates – the NOR gate and the NAND gate.

Logic gates

These two are commonly referred to as universal logic gates as they can be used to build numerous digital circuits including digital memory.

NOR gate

The output of a NOR gate is the opposite of an OR gate. You can think of this as an OR gate, followed by a NOT gate.

NOR gate

Here’s what the transistor representation of a NOR gate looks like. We have the two inputs and an LED connected to the output. When both the inputs are 0, the transistors will be switched OFF. R2 will provide the necessary path for the current which causes the LED to switch ON. If any of the inputs is 1, then it will cause the corresponding transistor to switch ON which will force the LED to switch OFF.

NOR gate

NOR gate

Let’s build and verify the truth table.

NAND gate

Similarly, you can think of a NAND gate as an AND gate, followed by a NOT gate. The truth table for a NAND gate is given above and it is also the opposite of an AND gate.

NAND gate

Here’s what the transistor equivalent looks like. If both the inputs are 1, then both the transistors will switch ON, which will pull the output to ground, switching OFF the LED.

NAND gate

NAND gate

Let’s build and verify the truth table.

This post concludes all the projects for BBox 1. The Kickstarter edition contains two additional PCBs kits and we will look at these in the next posts, which will then be followed by a quick recap of the main components.