I have the following circuit which attempts to turn on and off LED in a gradual manner (instead of having abrupt change between states).
So when I press S1, LED1 will light up gradually, thanks to C1's charging. My eye can observe a 1 second period till the LED fully light up. This works as expected. However, If I release S1 afterwards, LED1 will gradually turn off, but it take very long, like 30 seconds or so till the light completely vanishes.
So C1 discharges really slow, and I don't understand this behaviour. I thought C1's discharging process should be fairly fast, since there is only a 220ohm resistance (plus the diodes' resistance) between its two poles? Can someone explain to me what's happening here?