I assigned the following pin number to all inputs:

Input A - Pin1
Input B - Pin2
Input C - Unsure which pin to use
Vcc - 14
Gnd - 7

Since IC 7408 only accepts two inputs each time. Where do i connect the third input (C)?

Picture Source: From Doctronics

 

Why don't you start by looking for what you actually need ?

Much easier.

BTW, are you actually going to use a TTL part? They require too much power. Rather dated. Look for LS or CMOS.

 

Why don't you start by looking for what you actually need ?

Much easier.

BTW, are you actually going to use a TTL part? They require too much power. Rather dated. Look for LS or CMOS.

The picture embedded in my first thread. I'm not looking for performance parts. Just want to learn something out of a basic circuit.

3 inputs connected in 2 inputs AND gate to generate an output. I'm more concerned on where to connect the third input on the IC itself because i'm a little confused right now

 

The picture embedded in my first thread. I'm not looking for performance parts. Just want to learn something out of a basic circuit.

3 inputs connected in 2 inputs AND gate to generate an output. I'm more concerned on where to connect the third input on the IC itself because i'm a little confused right now

OK to the performance.

Since this is homework, I am not sure if you MUST consider that part.

The reasonable thing is to use an AND gate with three, four or eight inputs. (Unused ones should go to a logic "high" or "1").

To show you that more do exist.

 

Maybe you could use both inputs from gate A, plus one input from gate B (and the unused one, to "1").

Outputs of gates A & B as inputs of gate C. Resulting output is in the output of gate C.

Are you suposed to test this in a breadboard?

 

hi msie,
Consider what the Output state of the 7408 2 inp AND will be IF both inputs are high, logic '1'.
Then think how you would connect a 2nd 7408 to the 1st 7408 in order to get a 3 input AND logic function.

Do you follow OK.?
E

 

7408 does not have 3 input AND gates.

Like others said, you have several choices, you simply need to choose one of them:
* use different ic, that has 3 input AND gate
* use multiple 2 input AND gates to produce one 3 input AND gate
Pick one.

 

Looking at this from a Boolean perspective, remember the Boolean associative and commutative properties?

The associative property, essentially, says (AB)C = A(BC), where the commutative property says AB = BA.

So, if you are to implement ABC, you can implement it as A(BC), (AB)C, B(AC), or any combination thereof.

From another perspective, let Y=AB, or the result of one, two-variable AND operation. Then ABC = YC, another operation.

Once you understand the implications of what this means, knowing which pins to use will become apparent.

 

hi msie,
Consider what the Output state of the 7408 2 inp AND will be IF both inputs are high, logic '1'.
Then think how you would connect a 2nd 7408 to the 1st 7408 in order to get a 3 input AND logic function.

Do you follow OK.?
E

My bad. I should have left for him to do part of the effort to solve the problem.

Sorry for actually not helping him.

 

My bad. I should have left for him to do part of the effort to solve the problem.

It's easy to get carried away. I almost posted the full solution schematic.

 

It's easy to get carried away. I almost posted the full solution schematic.

Almost only counts in horse shoes and hand grenades.
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