Hardware logic gates for a simple demo with LEDs

Question

I need some logic gates for a simple demo like this one. I will use a regular breadboard and an Arduino UNO as a 5 V and GND supply.

I found these ICs from Texas Instruments SN74LSxxN (NOT, AND, OR, NAND, NOR, XOR). For my demo I only need two inputs (well obviously only one on NOT) and one output on each chip. I want to connect the output to a LED via resistor to demonstrate that for example 1 XOR 1 equals 0 (LED off), or NOT 0 equals 1 (LED on):

My LSs seem to work as expected without an LED connected:

int value;

void setup() {
 pinMode(10, OUTPUT);
 pinMode(11, OUTPUT);
 Serial.begin(1200);
}

void loop() {
 digitalWrite(10, LOW);  
 digitalWrite(11, LOW);
 value = digitalRead(5);
 Serial.println(value);  
}

…but it would be great to make an LED demo too.

These ICs are probably a better choice in my case?

• SN74ACT04N (NOT)
• SN74ACT08N (AND)
• SN74ACT32N (OR)
• SN74ACT00N (NAND)
• CD74ACT02 (NOR)
• SN74ACT86N (XOR)

For everyone who isn't happy with Arduino as power supply here an alternative circuit with the same question - which IC family should I use?

Update: Well, probably I should better use something like LogicBlocks for my demo. There is no NOR, XOR or NAND in this set, but it should be much easier to handle.

Answer 1

The SN74HC04 has a documented output driver capability of ±4 mA when running at 5V:

Assuming you are using red LEDs with a forward voltage of 1.6V (as I measured one of mine lying around on the bench to be), then to not exceed this you need to get a resistor of:

(5 - 1.6) / 0.004 = 850 Ω

A reasonable (and safer) value would be a standard 1k resistor, which you are likely to have lying around (and if not, get a few hundred of them). That would give you 3.4 mA current through the output pin, which is in range.

---

I found something very similar to my demo on YouTube ...

Yes, well, people on YouTube aren't always doing things exactly like they should. :)

See Mike Cook's tutorial The care and feeding of LEDs. As he points out, a lot of people use the wrong, or no, resistors because "it seems to work".

It may well seem to work for a while, but if you want a design that will last for a long time, you work within the manufacturer's specifications.

The problem with people disseminating wrong information is that someone will then copy it, and repeat it, and before long you find people saying "everyone does it this way".

Answer 2

The circuit I was looking for looks like this:

And the HC family seems to do the job. Thanks to dlloyd (link).