555 timer control pin

hi

i need to know how changing the voltage on the control pin changes the frequency of the output of a 555 timer running in astable mode

ive looked on the internet and all i can find is that "you connect the control pin top ground using a capacitor" there is no formula or explanation

Look at the schematic of a 555 on its datasheet.
The control pin affects the voltage where the threshold pin 6 is triggered when the capacitor charges up to it.
When the control pin voltage is increased then the timing capacitor muct charge to the new higher voltage that takes longer than before so the frequency is lower.
When the control pin voltage is decreased then the timing capacitor must charge to the new lower voltage that takes less time than before so the frequency is higher.

Note that the duty cycle also varies, the off time stays roughly constant but the on time varies. If you want the duty cycle to remain the same, then you need to add a divide by 2 counter.

can u pls explain the working of each part of the circuit in this link
**broken link removed**

The link is broken.

Before asking have you Googled for 555 tutorial and read the pages pointed to by the first three links?

Hero999 said:

The link is broken.

Before asking have you Googled for 555 tutorial and read the pages pointed to by the first three links?

Click to expand...

hero,
Link worked OK for me.?

fatima said:

can u pls explain the working of each part of the circuit in this link
**broken link removed**

Click to expand...

Did you read the explanation?

What didn't you understand?