74HC14 Circuit Not Working

[ludzinc]

Can you provide a pic of your layout?

This time don't unplug anything - show us the exact layout you are trying now.

[rx8pilot]

I doubt the scope is to blame, it just needs to be used correctly. All details as are important which is why more than one person has requested very specific information. You seem to be worried you will be judged on the equipment you have and that is blocking the help you are seeking.

You should be able to make this work with no test equipment at all - a low end scope is a nice bonus.



Sent from my horrible mobile....

[Zero999]

There could also be a problem with the 'scope or probe. Try measuring the resistance of the probe with a multimeter. It should be 1M on the x1 setting and 10M on the x10 setting.

[andybarrett1]

I doubt the scope is to blame, it just needs to be used correctly. All details as are important which is why more than one person has requested very specific information. You seem to be worried you will be judged on the equipment you have and that is blocking the help you are seeking.

You should be able to make this work with no test equipment at all - a low end scope is a nice bonus.

+1

[RyanG]

I believe the DSO138 does only 1X mode, and it is built into the board. The probe that it comes with has 0 ohms across it. I tore everything off the breadboard again today and rebuilt the whole circuit for about the 10th time, and it works.

[Zero999]

I believe the DSO138 does only 1X mode, and it is built into the board. The probe that it comes with has 0 ohms across it.

Then the probe or 'scope input is broken. 0 Ohms would cause a short circuit and it would behave exactly as you've described.

I tore everything off the breadboard again today and rebuilt the whole circuit for about the 10th time, and it works.

So is it working with the probe connected now? If it is, then it seems like 'scope or probe has an intermittent short circuit. Try flexing the probe's cable and checking the resistance at the same time. Another possibility is something metallic short circuited the input on the 'scope's PCB.

[RyanG]

It was working while controlling a LED. The scope has 1Mohm built into the board with no switch on the probe. I did not check the circuit with the scope.

[Zero999]

It was working while controlling a LED. The scope has 1Mohm built into the board with no switch on the probe. I did not check the circuit with the scope.

Well if what you said in the other post above "The probe that it comes with has 0 ohms across it." then you have a problem with the 'scope/probe. I was going to suggest you use another channel but I Googled the DSO138 and it only has one channel so you're SOL.

[Nusa]

The "probe" that comes with the DSO138 is literally a short BNC cable with two alligator clips on the other end. However, the BNC output is already compensated and measures about 1MOhm. There are two trimmer caps on the board to calibrate it.
https://youtu.be/F1oDhaqyIvk

[RyanG]

That is what I was trying to say. Now that I have this circuit working, somehow, I wanted to know the actual best way to do a PWM signal for the full range of duty cycle from 0%-100% without a micro

[StillTrying]

I'm amazed that people still think the '14 stuck at 2.4V problem was/is something to do with a scope probe, or a bad scope probe, when I was reproducing it for 2 hours in Reply#57.

That is what I was trying to say. Now that I have this circuit working, somehow, I wanted to know the actual best way to do a PWM signal for the full range of duty cycle from 0%-100% without a micro

https://www.eevblog.com/forum/projects/change-pulse-width-of-a-signal/msg1129000/#msg1129000

If you're not too bothered about the frequency changing a bit many other methods are available.

[stj]

2.4v should be impossible, unless it's the average of a very fast squarewave.
a frequency counter or similar function in a multimeter would be handy here.

[ebclr]

Duty Cycle from 0%-100 is impossible.

O% and 100% means no oscillation , no cycle  no duty

[Brumby]

Duty Cycle from 0%-100 is impossible.

O% and 100% means no oscillation , no cycle  no duty

From an oscillator output - I agree.  However, if you wanted to, you could design a circuit that would switch out the oscillator and connect the output to 0V or Vcc - which would effectively give you the 0%-100% range.

You could also program it out of a micro - if you were to include those in your range of chips.

[RyanG]

I understand that 0% and 100% aren't possible with oscillation. As far as the 2.4v thing it was definitely my cheap scope interfering, in my case. I'm sure it can be replicated in other ways.

[rdl]

You can get close to 0-100% with a 555 timer as long as you're not too concerned with constant frequency. Dave did this in episode #392 if you haven't seen it.

[Zero999]

The easiest way I know of to get 0% to 100% PWM, with jellybean parts and no MCU, is to use the LM393.

[RyanG]

This may not be the simplest way of doing it, but does this look like it would work? It works in everycircuit.

http://everycircuit.com/circuit/6706632576991232
I think it will only show in Chrome

[MK14]

This may not be the simplest way of doing it, but does this look like it would work? It works in everycircuit.

http://everycircuit.com/circuit/6706632576991232
I think it will only show in Chrome

No, not apparently showing in Chrome.

Ideally, it would be nice if you can post circuits in some kind of standardized format. E.g. image files.

Something which needs to go onto a weird website and/or needs downloading executables is not a good idea, for easy viewing on forums.

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(Load error: NaCl module load failed: PnaclCoordinator: pexe load failed (pp_error=-2).)

[rdl]

I had this in my notebook from a long time back. I didn't have time to build it again to test until today. It works okay and you may already have the parts. With a 10k pot and 0.1 uf cap I got from less than 1% to over 99% duty cycle at about 650 - 925 Hz.

[RyanG]

I thought that the website I posted worked in chrome no matter what. I sent it to other people to check. Here is the picture.

[StillTrying]

That can't be right.
Edity: The first inverter and resistor don't make sense.
Edity2: Is the value of R1 critical. 

[rdl]

It's not my circuit just one I found. Maybe I drew it wrong, but I ripped it up and built it again and it still works. Maybe someone else could give it a try? It's pretty simple and quick to build. Sorry for the poor quality image.

[rdl]

That can't be right.
Edity: The first inverter and resistor don't make sense.
Edity2: Is the value of R1 critical. 

1. I drew the circuit close to the way I originally built it on perfboard so it doesn't look the way it's usually shown.
2. The original circuit used a 4049 and I have R1 noted as "improves shape of square wave - use about 10x value of R2"

Maybe it's the different chip, but R1 seems to make little difference here. As a matter of fact, at higher values and with small values of C1 and R2, it causes the output to become a sine wave at around 10 times higher frequency than expected. The circuit seems to work fine without it and just a wire directly to the input of the first inverter.

[BrianHG]

In that schematic, shouldn't R1 be between the diodes and cap with the cap wired direct to the first inverter input.  Otherwise, when your trimpot is wired all the way to one side or the other, that circuit's output will sort of be short driving the cap distorting the second inverter's output when the trimpot is set to 0% or 100%.