TTL OR gate
Électronique /
Electronic
7400
One of the nice things about the Quad 2-input NAND IC in this project is the way the four NAND gates can be combined to make up other logic circuits.
It's possible to make up an OR gate from NANDs, as this Project will prove. Our last two Projects have given some clues about how we can use NANDs to make up other logic circuits.
Take a look at the schematic for this Project can you trace what happens from each input to the eventual output? (Sure you can -just give it a try.)
As build this circuit, be sure to place the Select Switch at B. When you're finished, put the power ON. Now press the Key. What happens to LED 1 ?
Release the Key and set the Select Switch to A. What happens to LED 1 now?
Keep the Select Switch at A and press the Key again. Any change in LED 1?
You saw that this circuit indeed behaves like other OR gates you've played with. Have you traced what happens from input to output yet? The answer's in the next column, but no fair peeking.
We can make up AND, NOR, XOR and NAND gates using the Quad 2rinput IC. Can you figure out how we would connect the NANDs in the IC to do this?
Take your best guess and make notes ... because we're soon going to find out.
