hello friend thank you i came to know about a good pulse width modulator with your post. you have to use two pots one for varying duty cycle and other for varying frequency. you didnt told at what voltage you want to operate. i suppose it as 3V and you have to connect 2K ohm resistor plus 1k ohm potentiometer and 100 ohm resistor in series between +VCC and Gnd. Now connect the tap of the potentiometer to MOD PIN to vary duty cycle (voltage at mod pin varry from 0.9v to 0.1 v to produce a duty cycle change from 0 to 100%)
to change the frequency you have to take one 500k ohm pot and make it short two terminals out off three terminals, finally you have to connect 500k ohm pot and 50K ohm pot in series between SET pin and Gnd. the maximum resistance value allowable between set pin and Gnd is 50K ohm to 800K ohm. so you can increase pot vaue up to 800K ohm.