Can someone explain why the circuit without diodes doesn't work properly? It still has different paths for the capacitor to charge and discharge. Charging uses left side of the potentiometer and discharging uses right side.

 

Please post the schematics for the two circuits, with designators for all components, so that we can see and discuss them.

 

Please post the schematics for the two circuits, with designators for all components, so that we can see and discuss them.

you don't see the pictures?

 

We don’t work with such pictures.
This is an example of a circuit schematics.

 

We don’t work with such pictures.
This is an example of a circuit schematics.

View attachment 361555

there is only a few components and you need a schematic for that?

 

there is only a few components and you need a schematic for that?

Yes.

It does not matter how many components there are. With a proper schematics with component identifiers, we can begin to discuss circuit details.

 

there is only a few components and you need a schematic for that?

Yup.
Schematics is the language of electronics, not pictures of PCBs or verbal descriptions.
We would have to draw the schematic from your PCB and that's not generally part of the free work we do here.

Are you telling us the circuit was built without a schematic?

 

Paraphrasing Rear Admiral Joshua Painter,

"Engineers don't take a dump, son, without a schematic."

ak

 

Yup.
Schematics is the language of electronics, not pictures of PCBs or verbal descriptions.
We would have to draw the schematic from your PCB and that's not generally part of the free work we do here.

Are you telling us the circuit was built without a schematic?

That is from a youtube video by "The Engineering Mindset". Oscilloscope guide.

 

That is from a youtube video by "The Engineering Mindset". Oscilloscope guide.

And there was no schematic in that video that you could screengrab and post?

 

Why not use this as an exercise in drawing schematics?
Convert the wiring diagram into circuit schematics.

 

That is from a youtube video by "The Engineering Mindset". Oscilloscope guide.

I'd suggest ignoring any content with pictures drawn like that. Clearly the person doesn't know what they're talking about.

 

Looks like you garnered the wrath of the cranky crew. A picture like that works well enough and is quite clear and straight forward especially for experienced and very talented guys like the above members.

 

Can someone explain why the circuit without diodes doesn't work? It still has different paths for the capacitor to charge and discharge. Charging uses left side of the potentiometer and discharging uses right side.

As configured from the image in post #1 seen below, it does work without the diodes to some extent.
100% to appx 30% duty cycle over a short span of the pot.
Then goes to zero output on the remaining travel which is more then 1/2 the total rotation.
Verified on a breadboard.

 

A picture like that works well enough and is quite clear and straight forward especially for experienced and very talented guys like the above members.

You forgot lazy.
I'm not interested in doing the work of drawing a schematic from a layout (although sghioto apparently is ) .
That's the TS's job.

 

As configured from the image in post #1 seen below, it does work without the diodes to some extent.
100% to appx 30% duty cycle over a short span of the pot.
Then goes to zero output on the remaining travel which is more then 1/2 the total rotation.
Verified on a breadboard.
View attachment 361577

Thanks. I just don't understand why it doesn't work properly.

 

I just don't understand why it doesn't work properly.

By 'properly', do you mean with a duty cycle varying from near 0% to near 100%?

 

By 'properly', do you mean with a duty cycle varying from near 0% to near 100%?

Yes. Like it works with the diodes.

 

Yes. Like it works with the diodes.

Why would you expect it to work the same with or without diodes?
The diodes isolate the charge resistance from the discharge resistance so that the two can independently control their respective times.
Without the diodes, the two resistances interact such that the full duty-cycle range cannot be achieved.

 

Therein lies your problem. The basic 555-timer astable circuit works for 50-100% duty cycle.
For lower than 50% you need the diodes.

See:
https://electronicsclub.info/555astable.htm

https://www.electronics-tutorials.ws/waveforms/555-circuits-part-1.html