Hello guys, I'm doing the logic gate OR, I simulated it on Multisim but I amn't obtaining the correct truth table, with all the inputs I obtained the turn ON LED. Am I doing something wrong?, thank you. (I take the circuit from the Datasheet of SN7432)

 

hi D.
I'm doing the logic gate OR
How are you driving the A,B Inputs.?

https://www.allaboutcircuits.com/textbook/digital/chpt-3/multiple-input-gates/

E

 

hi D.
I'm doing the logic gate OR
How are you driving the A,B Inputs.?

https://www.allaboutcircuits.com/textbook/digital/chpt-3/multiple-input-gates/

E

I think that with the switches is correct but I am not sure, I'm new with this

 

hi,
Try Pulling Logic High on the Inputs, ie: +5v
Ideally a change over switch Low , High... 0V , +5V

E

 

Ok, I'll try it, but the transistor Q1 and Q4 don't determine the inputs A and B?

 

hi,
In an actual TTL OR logic IC, the inputs would assume a partial High, but in Multisim, I am not sure what state the inputs would assume in simulation.
I do not use Multisim.

Try the Pull up suggestion see what we get.
E

 

Hmmm ok, I'll look, what digital circuits simator is well for this? I tried in Proteus but I obtained the same

 

hi,
If you get stuck, I will create the circuit in LTSpice, compare our results.

BTW: Is this a College assignment.?

E

 

No, I'm experimenting with the TTL taking advantage of the transistors features like the saturation and cut off checking the truth tables of the logic gates

 

The circuits inthe datasheet might need tweeks to make them work. Like places for leakage currents to go.

 

I am missing a resistor in series with LED1.

As others write, we barely know what the simulator does with open digital inputs.

 

hi 2902,
This is what I see in LTSpice, [ check the circuit for correctness]
Used a 500R for the LED.

E

 

Hi 2902,
Works OK for me.
I would not use 1N4004, say 1N914
or 2N2222 are over rated

E

 

Hi Eric.
Your output looks like B OR Not-A ?

 

hi Alec.
Looks OK to me,
E

 

Ah, I was reading the A trace wrongly. (On account of my poor colour vision the black dominates over the thin red line).

 

Hi 2902,
Works OK for me.
I would not use 1N4004, say 1N914
or 2N2222 are over rated

E
View attachment 219385

Hello Eric, thanks, I see that is correct, I downloaded the LTSpice. I have a question, how do you configurate the PULSE V2 and V3?, I don't understand the parameters

 

hi D,
Ref these two clips.
E

 

Ready, I obtained this, i think it's correct

 

hi,
Looks Ok.
Recommend that you use F4 and create a label for A, B, Out, then click on the label for plotting, the Red labels on my asc.
E