555 pot adjustment

[zesla]

ρHi there,

Can I make an astable oscillator out of a 555 to be adjust by a pot from 2Hz to morethan 100kHz or I need to change the oscillating cap as well?

Thanks

 

[ronv]

Look at figure 6 in this datasheet.

https://www.electro-tech-online.com/custompdfs/2011/05/LM555.pdf

 

[zesla]

Look at figure 6 in this datasheet.

https://www.electro-tech-online.com/custompdfs/2011/05/LM555-1.pdf

Thanks but What it does stand for really?
I seem I can not interpret it correctly!
Is it support my goal?

Thanks

 

[zesla]

Is that figure tell that I can use a 10K pot to get what I told at my first post? If so, what cap it suggest for this pot? a 0.001uf or...?

 

[Reloadron]

Read this link. Pay close attention to the section about Choosing R1, R2 and C1 and note the table on the right. To answer your question, no you will not get from 2 Hz. to 100 KHz with any single pot or capacitor combination.

Ron

 

[Boncuk]

Hi zesla,

fig.6 is clear to me.

Of course you need to change timing caps and resistors for a frequency range of 2Hz to 100KHz (several different values for R and C).

Boncuk

 

[zesla]

Read this link. Pay close attention to the section about Choosing R1, R2 and C1 and note the table on the right. To answer your question, no you will not get from 2 Hz. to 100 KHz with any single pot or capacitor combination.

Ron

Thanks sir,

So what to do to be able use a single pot for that range? Can I use a 4047 in astable mode instead to do so?

 

[zesla]

Hi zesla,

fig.6 is clear to me.

Of course you need to change timing caps and resistors for a frequency range of 2Hz to 100KHz (several different values for R and C).

Boncuk

Thank Boncuk,

Can you interpret it to me, for instance just for 10K slope? I want to learn how to read it.

Thanks

 

[zesla]

Any way to get a range of 1Hz to 100KHz square wave with any chip and just by a pot is welcomed. I do not like to use a switch on 555 to switch the timing cap.
Oh I forgot to say that the range that I need is not continues for 1Hz to 100KHz, just from 1Hz to 10Hz and from 90KHz to 100Kz is ok. As I told I don't want to use any switch....

 

[Reloadron]

Any way to get a range of 1Hz to 100KHz square wave with any chip and just by a pot is welcomed. I do not like to use a switch on 555 to switch the timing cap.
Oh I forgot to say that the range that I need is not continues for 1Hz to 100KHz, just from 1Hz to 10Hz and from 90KHz to 100Kz is ok. As I told I don't want to use any switch....

Just about all oscillators like this are based on RC timing networks. You should have gotten that much from the links provided. The fact that you could settle for 1 Hz. to 10 Hz. and 90 KHz. to 100 KHz. is of no consequence. You would still need two ranges. Even if you look at commercial function generators you will see they are ranged. There is no simple or easy way around this based on how such circuits actually work. What has been presented in this thread through links is as good as it gets. Beyond that, I don't know what to tell you.

Ron

 

[zesla]

Thanks,

Well yea, but I am looking for a trick, for instance change a pot (or use a gang/doubled pot or something so) or add a cap somehow to a pot (for instance connect it to the second pins of a doubled pot), or a similar trick to do the job. Any idea?

Thanks

 

[Reloadron]

The only idea is to use a switch as we have already beat to death. Additionally, you need to look at and understand both resistors rather than just a pot and see how they both figure into things. There is no easy way.

Ron

 

[zesla]

Well, the bellow freq can be steady to say 3Hz, but The upper freq has to change from 90KHz to 100Khz or a bit more,
I can remember that there are kinds of pots having an underlay switch, Can I use that SW somehow to get the 3Hz and use the pot itself somehow to get the upper range?

?Thanks

 

[Reloadron]

Yes, there are pots like this one in the Honeywell Clarostat 381 series that still come with a switch on the back. Actually it would be a 381NS10K for a 381 series with switch on back 10 K pot.

How you choose to configure this is entirely up to you. You have been given all the tools you should need to design what you want. Maybe someone else has further thoughts? I am done.

Ron

 

[zesla]

Thanks Ron,

Well I don't want to use an external Switch just want the pot itself does everything, It's no matter if it comes with a Switch, I can just turn the pot till I open/Close the SW so that I get the lower constant freq.
Unfortunately I have no Idea about the configuration as well,

 

[carbonzit]

That pot with attached switch won't do you any good. It just opens the switch at the end of travel (CCW), like a power-on switch as part of a volume control.

There are pots that have toggle switches that are activated by pushing the shaft in; would that work for you? Push in for one range, push in again for the other range, with the pot position unchanged.

 

[Dean Huster]

Wanting a circuit that can adjust from zero to infinity with one single 270° rotational control is like wanting a car that will move the steering throughout it's entire range with just a 1/4° wiggle of the steering wheel. Not practical. Finding a control with a sufficiently "infinite" adjustment resolution is impossible. Even if you could find such a thing, setting the control to an exact output (frequency in this case) would be impossible. Most circuits will not work over more than a 1:1000 range if even that wide. That's why we have range switching and coarse/fine adjustment controls.

 

[colin55]

Use one gate of a 40106 with a cap and pot to get from about 1Hz to 100kHz. The problem is this: You will be rotating the pot very little from about 50kHz to 100kHz

 

[ronv]

Wide range

Here is one that might work. The pot will need to be a good ten turn one as the circuit will be very nervous.
Run only on 5 volts.