What value of the R1 to change the off delay to 3secs only?

ThankYou

 

The schematic notes say R1 of 1M = 20 seconds.

So to convert 20 secs to 3 secs you need approx;
1M /20 *3 = 150k (150000 ohms).

If you want better than that, you can replace R1 with a 50k resistor in series with a 500k pot. That will give an adjustable time delay from approx 1 sec to 11 seconds.

 

In a one-shot C starts charging from gnd. so time is close to R X C so for 3 sec, R might be close to 300k.

 

sir , can i replace C547B transistor to any NPN or 2n2222 transistor? and if i put a 2pcs 12v relay any thing that can affect the off delay?

 

bc547 / 2n2222 are general purpose npn transistors, only thing you'd need to worry about there is pin configuration and data sheets are available providing google's not broke where you reside.

and why 2 relays? get one with higher rating or more contacts.

 

If the C547B transistor is the BC547B the you can use 2n2222 to replace it.
Why you want to use two 12V relays? (one 2N2222 for two 12V relays seems ok, but you still need to care the temperature)
If you need more contacts then you can choose two sets of contacts, you got 6 pins to use.

 

the question is ..... C547B and BC547B same?

yes ! i can use 6pins relay anyway