Exhaust Fan oscillation circuit

In the "Exhaust Fan" in this circuit is different, due to the increase in the circuit of the diodes D1, D2 and adjustable potentiometer RP, the situation changed. In this oscillation circuit, although its oscillation frequency is immutable, but its pulse duty cycle can be adjusted by RP and change. This is due to the addition of a diode, a capacitor C1 charge and discharge circuit and different than before. Wherein the charging circuit into the power supply through R1, the upper half, VD2 to the capacitor Cl RP. The positive electrode of the capacitor discharge circuit by the capacitor through VD1, R2 and RP second half to 7 feet. Circuit capacitor C1 is fixed, but its charge and discharge resistance value can be adjusted by changing the position of the RP.