TTL inverter
Électronique / Electronic
7400

What "TTL" meant?

Did you say transistor-transistor logic? We hope so, because that's the correct answer.

TTL devices have largely replaced DTL because they are operate faster and are cheaper to operate.

The Quad 2-input NAND IC used 7400 is a TTL device. It can be used to make up a wide variety of circuits - here we'll use it in an inverter.

You can see from the schematic that we use two of the four NAND gates in the IC. As you build this Project, set the Select Switch to A.

Turn ON the circuit, and you'll notice that both LED 1 and LED 2 aie off. Since the output is 0, the input must be 1? of course!

Now set the Select Switch to B and both LEDs come on, indicating you're inputting 0. You can see why this happens by looking at the schematic.

With the Select Switch at A, both inputs to the two NANDs are 1. That means the output of both go to 0 (and out go the LEDs). But when the Select Switch is set to B we no longer have all inputs at 1 and the LEDs come back on.

One of the amazing things to think about is to remember how large the RTL and DTL circuits were that we played with in earlier Projects.

Believe it or not, four circuits Like that have been shrunk down to fit inside that tiny IC! (Theje's a special type of IC, a bit bigger than the two in your Kit, which are actually computers shrunk to miniature size. They're called microprocessor's,)

The process which lets us put several circuits inside just one IC is called large-scale integration (LSI). You'll see this term often used to describe ICs.