I set up a basic test using a 74LS04 to switch LEDs on button press. The following setup works fine:
Why doesn't the following work?
I am slightly confused? any insight would be appreciated.
1: Where are VCC and GND connected?
2: AFAIK 7404 has an open collector output, that means it can only sink a current.
3: Same goes for the inputs: they are "open emitters", so you can only connect them to GND via a switch.
1: Where are VCC and GND connected?
2: AFAIK 7404 has an open collector output, that means it can only sink a current.
- Incorrectly, King Bob, check the wiring.
- They have totem pole outputs, they can sink and source current.
You MUST put resistors in series with your LEDs, about 220 Ohms or so. You have probably popped the LED connected to the button.
Your right hand LED is the wrong way round anyway.
All your connections are wrong, check the datasheet for the 7404.
Erik_Baas:
1: Where are VCC and GND connected?
Vcc is the Red row and Ground the Blue.
Erik_Baas:
2: AFAIK 7404 has an open collector output, that means it can only sink a current.
3: Same goes for the inputs: they are "open emitters", so you can only connect them to GND via a switch.
Is there a 74XXXX that does the exact opposite? Or one that does both?
2: Ioh max = -0.4mA, Iol max = 8mA. That's not a totem-pole. (data sheet).
2: Ioh max = -0.4mA, Iol max = 8mA. That's not a totem-pole. (data sheet).
It's not open collector either. I checked my very ancient copy of The TTL Data book for 7404.
I don't think King Bob has a single wire in the right place...
Vcc is the Red row and Ground the Blue.
I think we both want you to look a bit more closely at the other ends, the ends that go to the 7404.
PerryBebbington:
It's not open collector either. I checked my very ancient copy of The TTL Data book for 7404.I don't think King Bob has a single wire in the right place...
As I said The wiring in image 1 works fine, I have it hooked up exactly like that on my bread board.
I see what you mean, It is mirrored in the drawing... It may not be obvious but pin 1 (Vcc) is at the top right. Give me a second Ill re-friz it.
As I said The wiring in image 1 works fine, I have it hooked up exactly like that on my bread board. It may not be obvious but pin 1 (Vcc) is at the top right.
What makes you think pin 1 of a 7404 is Vcc? Or that pin 8 is 0V?
I have fixed the images
Erik,
I agree it can't source much current, which is the important point. I still think it's a totem pole output, but that's an academic point that doesn't help Bob.
What exactly is a negative current:
High-level output current −0.4 −0.4 mA
Direction of current flow.
- goes out of the output (sourcing current).
- goes into the output (sinking current).
I have fixed the images
The LEDs are the wrong polarity in the second image.
Still no resistors so you might have popped either or both LEDs.
You can ignore the little argument between me and Erik, his point is right, the 74LS04 cannot source much current. It might light LEDs dimly if you are lucky, but don't count on it.
Well, it's a fun ("educational") use of an obsolete and otherwise pretty useless IC that you would - should - not use in a serious project, so we shall not be too worried. 
Paul__B:
Well, it's a fun ("educational") use of an obsolete and otherwise pretty useless IC that you would - should - not use in a serious project, so we shall not be too worried.
Unfortunately I need it for one of my projects. Why is it obsolete, and what IC replaced it?
Unfortunately I need it for one of my projects. Why is it obsolete, and what IC replaced it?
It's ancient. Was good in its day. Don't know what replaced it. My preferred inverter was the CMOS 40106. All sorts of uses. Don't know if it would work for you as I don't know what you are doing. (40106 also ancient).
74HC04 AND 74HCT04