I searched about this and each explanation did not make any sense,my explanation is that when the OUT pin is HIGH the transistor turns on and the capacitor charges,also the led turns on gradually because the capacitor voltage rises,but when the OUT pin is off ,the capacitor discharges(trough the transistor) and the transistor stays on until the capacitor is fully discharged and when the OUT pin is HIGH it repeats all over again.Am I wrong?
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Best Answer
You're fairly close with that analysis.
Q1, the transistor is used as an emitter follower, in this configuration it only accepts a small current into the base. this is because the transistor conducts so that the voltage on the emitter rises until it's close enough to the base voltage to prevent most of the current from flowing into the base.
C1 is charged and discharged mostly through R1
The varying voltage on the capacitor causes a varying voltage at the emitter which causes a varying current through R2 and the LED.