IC possibly malfunctioning

Thread Starter

GTeclips

Joined Feb 18, 2012
96
Hi all,

I'm working on a small little circuit, and I'm confident the logic is correct, and I believe the wiring is also correct. But it is not working, and I believe the IC I am using is to blame.

I'm using the NTE74C04 (http://www.nteinc.com/specs/7400to7499/pdf/nte74C00_20.pdf) which is a hex inverter. I have each input wired to the negative buss with a 10k Ω resistor, and I gave it a 9v power supply. The problem I am having is I can get three of the NOT gates to work, but when I set the input of a forth one to high, in output remains high. So basically only half of the chip can work at one time.

Can anyone explain this?

Thank you!
 

Thread Starter

GTeclips

Joined Feb 18, 2012
96
Okay. I'm not good at diagramming the circuits, so I will just post post a picture of the logic diagram an what I want it to do, and a picture of the circuit I currently have. I don't know when I will post it, but I will try to be quick with it.
 

Thread Starter

GTeclips

Joined Feb 18, 2012
96
I know this image is hard to follow, but it is the best I could do.



When switches 1, 2, 4, 5, 8 are high, and 3, 6, 7 are low, the LED will light, and only when these are in the correct combination.

I had a logic diagram, but photo bucket wasn't liking it, so this picture is the best I can do.

*EDIT* Oh yeah, I have the buses reverse of what you are supposed to (I think), upper is positive, lower is negative.
 

tshuck

Joined Oct 18, 2012
3,534
You can upload images in your post using the paperclip icon above the text box.

I'm not following what you have done? You have one output, yet expect other outputs to affect the LED? The way you have it hooked up, if switches 1,2,4,5,or 8 are closed, the LED will light.

Your output is only dependent on 1A, and the output is 1Y....

...it also looks like you have two outputs tied together! BIG no-no....
 
Have you tied all of the outputs of the inverters together? That can only be done on a "open collector" output logic gate. What are you trying to do with this circuit?
 

tshuck

Joined Oct 18, 2012
3,534
You need some additional logic chips, open-collector, or tristate inverters to do what you are trying.


The poor little inverters are attempting to drive the logic HI while some others are attempting to drive it LO. Which one wins out depends on the device...if it doesn't die first....
 
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