Logic Circuits

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ladyphoebe15

New Member

• Aug 16, 2014

• #1

So i was using the 3 basic gates IC (7432, 7408 and 7404) and when i use the 7432 the output was always high but the inputs are low or simply, 0 + 0=1.why is this happening and how to solve it. I tried using different 7421 IC's yet with no changes. I would like know other tips as well inbreadbarding.

 

Ian Rogers

User Extraordinaire

Forum Supporter

Most Helpful Member

• Aug 16, 2014

• #2

Can you sketch your circuit... Something else may be pulling the output high..

 

audioguru

Well-Known Member

Most Helpful Member

• Aug 16, 2014

• #3

I have not used nor thought about old TTL logic for about 38 years since I used Cmos logic ever since. This must be for school work.
I remember a 7404 is a bunch of inverters and a 7408 has quad two-inputs AND gates. Google says a 7432 is a bunch of OR gates.
On the 7432, when either input is high then the output is supposed to be high. A 7421 has nothing to do with it since it has dual 4-inputs AND gates.

 

L

ladyphoebe15

New Member

• Aug 16, 2014

• #4

I also encountered problems like even though the output should be 0 which will not light the led but the led still ights up even though its a little but when the output is high, the led lights brightter.

 

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DerStrom8

Super Moderator

• Aug 16, 2014

• #5

Is that your circuit??

Have you tried testing the chips individually? How are you powering them?

 

audioguru

Well-Known Member

Most Helpful Member

• Aug 16, 2014

• #6

I suspect that the circuit with the hundreds of gates is built on a solderless breadboard that causes them to oscillate.
The schematic is missing many 0.01uF or 0.1uF ceramic supply bypass capacitors that helps the gates to stop oscillating.

 

DerStrom8

Super Moderator

• Aug 16, 2014

• #7

audioguru said:

The schematic is missing many 0.01uF or 0.1uF ceramic supply bypass capacitors that helps the gates to stop oscillating.

Click to expand...

Good catch!

 

manoj soorya

Member

• Aug 27, 2014

• #8

Hi

You can use Proteus for simulating the circuit directly....

I can upload the proteus file latter, If you want...


Thanks

Manoj Soorya