Digital counter for counting to e.g 4 or 8

[lykkedk]

Hi.

I was hoping someone could help me, solving this thing

I need a digital 'logic' driven by +5 V, simple count-unit, which can count to e.g 4 or maybe 8. It must count with a single +5 v, comming from an opto-coupler. The output of the opto-coupler will last 2-3sec. each time.

The count signal is comming from the 'ringing-tone' from my telephone, going through the opto-coupler.

When the circuit has counted 4,5 or maybe more 'rings', it must go 'high' giving me 5v at the end, so that i could drive my relay.

I think that D-flip-flop's (e.g 4013bc), could be used somehow, but i'am not sure it's the easiest way doing this.

Thanx in avance

Jesper.