INDEX

Now you try for a circuit which produce 50% duty cycle using Ra=Rb and a diode. First you try and see the circuit diagram below

Here you can see that we just connected a diode in between pin7 and pin6,see the directions of the diode. Now when charging occurs capacitor charges through Ra only because forward resistance of the diode is very small and current will flow through the path of minimum resistance, so no flow through Rb during charging. During discharging no current flow through the diode because the capacitor is already charged with + ve on Rb side and -ve on ground side. We normally use electrolytic capacitor as C, we use ceramic also. So the diode is reverse biased during discharging making a high resistance compared to Rb, so discharging time depend on Rb. You can think this way also, Rb <<diode reverse resistance and Rb and diode in parallel, when two resistors are in parallel the effective resistance will be the resistance of the lowest one(here diode reverse resistance is too
high).

In this circuit Ra=Rb. Then only you get 50% duty cycle. You can connect the output of the astable multivibrator to a speaker( i am talking about a small buzzer normally works with voltage greater than 7V, ideally 12V) through a capacitor(capacitor should be of high value 10uF etc..) then you can hear sound. If you change frequency then you can hear a different sound, change duty cycle also and see the variation in sound.