Hello everyone.

I am asked to design a circuit which contains a square wave generator that generates different duty cycle waves. Our asisstant said that we should use capacitor with different charghing and discharging times.
I would be grateful if you guys help me.

 

Read the applications section of a NE555 data sheet to see if you can gets some ideas.

 

Hint: you can use diodes to get independent control of charge and discharge times.

 

Use a microcontroller and you've solved the whole thing: simple and elegant. For example, a microcontroller Attiny25/45/85, it is sufficient for such a circuit (assume that a frequency of about 4kHz is enough).
To change the duty cycle you can use as reference:
- voltage on the MCU's ADC input;
- some buttons to increase and decrease the duty cycle;
- a timer.
So, the solutions are, important to want to do something.

 

https://www.google.com/search?newwindow=1&site=imghp&tbm=isch&source=hp&biw=1366&bih=642&q=variable+duty+cycle+pwm+circuit&oq=variable+duty&gs_l=img.1.2.0i5j0i24l6.6068.11872.0.18502.13.12.0.1.1.0.63.579.12.12.0....0...1ac.1.32.img..0.13.579.UIys_5tT5rM#imgdii=_
try this link.......

 

Use a microcontroller and you've solved the whole thing

Seeing as this is in the homework help section, I expect the OP is not allowed to use a microcontroller. S/he specifically said that it needs to be adjusted by changing capacitor charge/discharge times.

@the OP:

As the others have mentioned, a 555 timer is a great way to go. You can use diodes to adjust the duty cycle, and the regular 555 circuit for adjusting the frequency.

As a general rule here at AAC we are not allowed to do your work for you. In fact, you're supposed to try it on your own first, and if you have problems, THEN ask here. You are supposed to show what you have tried so far and we can help point you in the right direction from there.

Just something to keep in mind.

Regards,
Matt