Hello everybody i am configuring a 100% duty cycle with two 555 and i have a frequency who vary from 30 hz to 635HZ and i am asking if it is normal that the frequency changes(with frequencymeter) while im turning my potentiometer (i have a scope and i have 100% dutu cycle)
thank you

 

100% duty cycle means that your output stays high level all the time....in plain English, it is not oscillating.

 

Shouldn't vary that much, do you have access to a 'scope?
Max.

 

What is your goal for freq accuracy/stability versus the duty cycle control ?

1%, 10%, ????


Regards, Dana.

 

Posting a schematic always helps with our answers.
Otherwise we are just guessing.

 

@MATT838383 Are you using something like this?
http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
Max.

 

0-100% duty cycle but is the frequency fairly constant?
For stability you need the 555 version with the dual diodes.
Max.

 

MaxHeadRoom
No it is not constant!

 

Thats a clever 555s PWM method, adjusting duty cycle should not affect the frequency

 

Hello so what the solution for that?
thank you

 

What is your goal for freq accuracy/stability versus the duty cycle control ?

1%, 10%, ????

Whats your input signal look like, is it a logic signal or analog or ????

You need to indicate to the forum your performance goals so we can give you
good advice.


Regards, Dana.

 

We could use a look at your schematic. As has been said - without seeing what you did we're just guessing.

Here's how I used a single 555 to control the speed of a blower. Pin 3 of the 555 goes high and low, charging and discharging the gate of the IGBT. The two steering diodes control nearly the full 100% range of speed. The frequency is set by the 104 cap. (0.1 µF) and the 50KΩ pot. The 10Ω resistor is there to prevent fully shorting the output to pin 2.

 

Hello so what can be the problem for that?

The problem is, you haven't posted a schematic of your circuit.

 

hi Matt,
Minor drawing error.
E

 

Hello Eric! a mistake!

 

Tonyr1084
Hi it is not exactly what i want! take a look above

 

can somebody answer me?

 

can somebody answer me?

About what?
Or are you referring to your original question?

Why are you using a dual 555 circuit, when the single 555 circuit that Tony posted in post #2 should do what you want?

 

I have found that the circuit in post #6 is best for stability using the dual diodes at the pot.
Only one 555 needed.
Max.

 

Thats right thanks to everyone!