The ultimate clock-problem (74LS42)

Isolate the individual IC's from each other and test each stage independently. You might add a power on clear so you automatically start at zero.

add a pull-up resistor to the push-buton, don't leave it floating

If these are outputs of the LS42, then you have either a defective chip or a solder bridge. A properly-operating LS42 will _never_ have more than one output active at a time.

And the different sequencing tells me that you've got bit lines crossed, unless the solder bridge accounts for it as well. (or a different solder bridge).

Also, as John Fields has said, your pulldown resistor is pointless at best.

Good Luck! Rich

Btw, here's the schematics:

-- Rikard Bosnjakovic

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The button isn't floating, I just didn't include the actual debouncer-circuit since it can be found in the thread "Trigger pulse from a push button" in this group, in the article dated 2005-03-25 by John Fields (who made that circuit for me).

When the button isn't pressed there's +5V to the pulse-input, and when pressing the voltage drops to 0V.

Why do I need a resistor for each led, when the 74LS42 only outputs to one LED at a time? Sure, it doesn't output to one individual pin in this case, but in proper cases?

I saw Rich's post as well and rebuilt your schematics into a TTL-one. It looked like it worked on my breadboard, but this could ofcourse be the source of the error as well. I do not own an oscilloscope so I cannot check if my solution is proper or not. A good guess is that my solution is not proper.

Also, my ISP does not import binary-newsgroups. Would you mind mail that schematic to me, or put it anywhere where I can reach it?

Thanks.

Lol :)

For the record, I moved the ICs from the veroboard and moved them back to the breadboard following Lord Garth's advice "Isolate the ICs and test them independently". I tested the 74LS192 by itself (using my TTL-button) and verified that the bit outputs are correct, and that the debouncer works as a charm.

Then I added the 74LS42 to the board altogether with 9 LEDs. Works perfectly, each LED is staged/counted up one by one and even if i keep the button pressed none of the LEDs will flash or blink, and no two LEDs will be lit at the same time.

Therefore I'm believing Rich is right. The ICs are not defective and so is not the debouncer. There must be some solder bridge somewhere. Good thing is that I've got a bunch of dentist hooks so I can peel around at small areas. First time in life I'm grateful to dentists I think. Bad thing is that I don't have a lens or microscope or anything that can extend my visual tracking. But atleast I now know what to look for.

And the best part, I'm the kind of person who has a strong belief in that you cannot learn things properly if you never make any errors. Making these kind of errors and having this newsgroup giving tips and general guidance, my path to learn electronics is going to be pretty nice to walk on.

After 6 straight hours of finding the problem, I think I've found a possible problem of why my circuit won't work. The 74LS192 is not a

So, to conclude the problem: 74C192 controls the 74LS42, which sends a signal to the inverter-NOR 74LS02, which sends a reset-signal back to the 74C192. So I guess it looks something like this:

CMOS -> TTL -> TTL ^ | \----------------/

I do not have any other (TTL) 192-ICs and no other (CMOS) 42-ICs, but I have one CMOS-NOR if that is of any help.

Putting a resistor there didn't help, so I replaced the NORs and resoldered (too bad 4001 and LS02 isn't pin-compatible). That solved the sequence, and I got 1-5 as I though.

However, I still had the LED 1-2 lit at the same time-problem, so I measured all over with my multimeter. I found that when the counting arrived at 6 (where it was supposed to reset), LED 1 and 2 flashed and the counter suddenly was at 7. Pressing the button made it count to 8 and 9 and then starting over.

I thought the LS02 was broken so I replaced it with a new one. Still the same error. I measured the voltage at the input pins of the NOR with my Fluke and found it to be 1.8V, which is illegal and I had no idea how the LS42 could output an illegal current.

Then I got an idea, similiar to this one: Perhaps the NOR has got slower gates than the reset of 74C192, that when pin 6 goes from high to low and in the middle of the NOR-operation (or similiar) the reset is due, which confuses the circuits and skips the reset.

(atleast when I'm writing this now it makes sense, resetting a bunch of flip-flop is probably faster than performing a logical NOR)

So, my next problem was how do make some sort of delay for the gate, so the NOR would be proper. I digged around in my box and found a new

The space around the ICs is dead tight so the cap couldnt be soldered there. I cut a wire, soldered and moved the cap 6-7cm away from the IC and tested again. Didn't work. The distance to the cap was probably too long (considering its storage-size), so I soldered it straight under the IC-socket, and now everything works as a charm.

The units above the 1nF-caps is 1.5nF, and the next one is 1uF. Without testing (and w/o yet knowing the valuable math) that value felt too much for the gate, so I kept the 1.5nF-one.

Thank you John and Rich for your help. Without the debouncer I would have to wait 1-2 weeks before getting the components I've ordered, and I'm way too impatient for that.

Two final questions:

1. Is my hypothesis about the time for the reset and NOR correct, or is it complete rubbish?

1. The reason that the 1nF didn't work when soldering it 6-7cm away from the IC, is it because of the reasons I wrote above?

Welcome to the loony bin! ;-D

Cheers! Rich