the gates to be used were not specified, if it is possible, I need to use the simplest available gates. The thing is that I don't even know how to use 555 timer in this case,
A couple of handy ICs that you will need are BCD to 7-segment drivers.
There are TTL versions in the 7446, 7447
CMOS has the 4033, 4511 and a few others.
You will need some decimal/BCD counters (NOT Decade/Johnson counters). I suggest that you avoid HEX/binary counters, as that will make extra work for you.
You may also need AND, OR, NAND, NOR, XOR gates and inverters.
The 4093 is a very handy IC to know about; it is a quad Schmitt-trigger NAND gate. You can construct any other logic gate using combinations of NANDs. http://en.wikipedia.org/wiki/NAND_logic
The Schmitt-trigger input is very useful for "squaring up" slowly transitioning waveforms.
There are lots of chips that count either to 6 or to 10, with mates that can decode that to a digital display. With TTL it is a 7492 and 7490, not sure of the CMOS numbers (but I know they are out there).
It occured to me after seeing Wookie's reply that you meant the project as a whole, not just the 555 clock.
Not really, 1 second frequency. Width is ½ second, assuming a symetrical square wave (which isn't really important).
You have the formula's on the sheet I posted, try using the procedure I posted. Start with a 1µF cap, 1KΩ for Ra, and work out the resistor value for Rb.
As for the rest...
This is a generic block diagram I drew up a while back. The first 2 counters are replaced with your 555 timer time base.
mr.Bill, I have succeeded in connecting the six 74ls160 ICs to the 7-segment displays. I tried giving clocks with different frequencies from a function generator. The seconds, minutes and hours are being showed correctly. --:--:--. My problem now is to get the right input frequency to the first counter, what's the right frequency? I want to try supplying it firstly using the function generator then I will design the 555 timer according to this frequency.
(first counter is for seconds --:--:--'the one in red')
The first counter is 1 Hz. You have all the information in front of you, I've given you two of three components to make a 555 1 Hz oscillator, the rest is algebra.